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Effect of relative humidity on the unlubricated wear of metals
Abstract
Experiments were carried out to investigate the effect of humidity on the wear behaviour of same metal combination, i.e. steel–steel and aluminium–aluminium. The sliding wear of steel was found to increase by nearly 1.5 orders of magnitude when the relative humidity (RH) of the surrounding air decreased from 80 to 28% RH. At low humidity, both delamination and adhesion wear occurred. At high humidity levels, both delamination and adhesion wear took place at a relative small scale and the frictional force was considerably lower than that obtained at lower humidity levels. It is proposed that the low wear occurring at high humidity levels is due to the inhibition of these wear mechanisms by the formation of interfacial layers, possibly iron hydroxide and ferri-oxide-hydrates, and the adsorption of water on the worn surface in addition to the normal atmospheric oxidation. Increasing the humidity from 28 to 80% RH increased the wear rate of aluminium by nearly half an order of magnitude. It is proposed that at higher humidity levels, water vapour adsorbs on both the freshly created surface and wear debris generated and therefore the wear debris egresses easily from the contact area without adhering to the parent surfaces. Lack of adhering wear debris exposed the worn surfaces to metal–metal interaction.
... Once the wear debris was formed, it would be entrapped at the rubbing surfaces for a period of time and act as a load-carrying plateau. Under different environment conditions, the dwell time of debris was different [10,11]. The oxidation products and oxidation rate of wear debris were closely related to the environmental temperature and humidity. ...
... The oxidation products and oxidation rate of wear debris were closely related to the environmental temperature and humidity. The oxidation rate of the wheel-rail surfaces and the wear debris decreased with the decrease in the temperature and humidity [10,13,14], which had significant influences on the wear and damage behaviours of wheel-rail materials. Shi et al. [14] studied the adhesion properties of wheel-rail under dry and contaminants conditions at low temperature. ...
... The adhered wear debris layer on the rail surface, the wear debris spots on the wheel surface (Fig. 7a) and the finer ejected wear debris particles (Fig. 14e) after testing at − 40 • C extended the dwell time of wear debris. The long dwell time of wear debris could reduce the wear of wheel and rail materials [9,10,16]. It was worth noting that though the rail surface was protected by the wear debris layer, the reduction of rail wear was not obvious at − 40 • C. ...
The objective of this study is to investigate the wear and rolling contact fatigue (RCF) damage of wheel and rail materials under alternating temperature conditions. Two series of rolling-sliding tests were performed: (1) at 20oC for 75,000 cycles, and then continued at -40oC for 10,000, 30,000, and 75,000 cycles, respectively; (2) at -40oC for 75,000 cycles, and then continued at 20oC for 10,000, 30,000, and 75,000 cycles, respectively. The results indicated that the decrease in the temperature would alleviate the wheel wear due to the formation of wear debris layer. Both the rising and dropping of the environmental temperature during the tests could lead to the increase in the rail wear. Besides, the decrease in the temperature could increase the plastic deformation and work hardening of wheel and rail discs. In addition, the crack initiation was correlated with the behaviour of plastic flow on the wheel. At 20oC, long single cracks initiated and propagated along the highly deformed ferrite boundaries. At -40oC, white-etching layer (WEL) was observed only on the wheel surface, which was mainly attributed to the severe plastic deformation. Then, the refined ferrites and WELs were the main crack initiation sources on the wheel.
... The analytical model for the clean disc, created as an approximation of measured data, predicts the effect of RH on CoA as a linear function with a very good determination coefficient. However, previously published studies [17,18,[30][31][32][33][34] have reported an uneven trend. Some of them [30][31][32] point to a more significant drop in friction accompanied by an abrupt change in wear mechanism, although the transition level of RH varies across the studies between 15% [30], 45-55% [31] and 50 a 60% RH [33]. ...
... However, previously published studies [17,18,[30][31][32][33][34] have reported an uneven trend. Some of them [30][31][32] point to a more significant drop in friction accompanied by an abrupt change in wear mechanism, although the transition level of RH varies across the studies between 15% [30], 45-55% [31] and 50 a 60% RH [33]. Other studies predict the trend as bilinear, wherein the Fig. 9. Condensation during tests with the clean disc (a) and contaminated disc (b). ...
... Note that there is also a question about the effect of sample material. From this perspective, the most representative studies are those using a real rail and wheel steels [17,18,32,36,38]. Nevertheless, a fundamental discussion on the effect of relative humidity on friction and wear comes from studies using more general materials such as carbon steels [31], austenitic stainless steel [33,39] and bearing steel [30,40] and the trends are qualitatively similar. ...
Low adhesion problem is one of the major problems for railways all over the world because this phenomenon can occur anytime and anywhere. To investigate when poor adhesion conditions can be expected in real operation, a ball-on-disc tribometer with a climate chamber was employed to simulate rolling-sliding contact under various environmental conditions. Clean and contaminated discs with leaf extract were used to simulate different surface conditions. Results indicate that contact operating under rolling-sliding conditions is more prone to the occurrence of low adhesion than found by others for pure sliding contact. Very low adhesion (≤0.05) were identified for contaminated and oxidized specimens operating under humid and wet conditions. For clean surfaces, low adhesion (≤0.15) were found under dew conditions.
... Olofsson and Sundvall [9] demonstrated that the friction coefficient can be reduced from 0.65 at 40 % relative humidity (RH) to below 0.4 at 95 % RH . Liew [10] reported a transition from high to low friction in the RH range of 50-60 %. Hardwick et al. [11] investigated the influence of NaCl application on the oxide formation and adhesion coefficient. ...
... This phenomenon seems independent of temperature and pretreatment, though the absolute value of the friction coefficient indicates some differences. Such phenomena were also found by Liew [10] using a pin-ondisc test rig but running at a different sliding speed. Hayashi et al. [21] also reported that the coefficient of friction had huge reduction from 4 % RH to 35 % RH, but stabilized when the RH was increased further to 63 % at 28°C. ...
... Second, increased water vapour will slow the oxidation rate because the vapour occupies the surrounding atmosphere. In this sense, water or high humidity can inhibit oxidation [28], though it can promote the formation of iron hydroxide (rust) and ferric oxide hydrates [10]. In addition, condensed moisture can give rise to boundary lubrication between surfaces, which can also cause electrochemical corrosion on metal surfaces [29]. ...
... Olofsson and Sundvall [9] demonstrated that the friction coefficient can be reduced from 0.65 at 40 % relative humidity (RH) to below 0.4 at 95 % RH . Liew [10] reported a transition from high to low friction in the RH range of 50-60 %. Hardwick et al. [11] investigated the influence of NaCl application on the oxide formation and adhesion coefficient. ...
... This phenomenon seems independent of temperature and pretreatment, though the absolute value of the friction coefficient indicates some differences. Such phenomena were also found by Liew [10] using a pin-ondisc test rig but running at a different sliding speed. Hayashi et al. [21] also reported that the coefficient of friction had huge reduction from 4 % RH to 35 % RH, but stabilized when the RH was increased further to 63 % at 28°C. ...
... Second, increased water vapour will slow the oxidation rate because the vapour occupies the surrounding atmosphere. In this sense, water or high humidity can inhibit oxidation [28], though it can promote the formation of iron hydroxide (rust) and ferric oxide hydrates [10]. In addition, condensed moisture can give rise to boundary lubrication between surfaces, which can also cause electrochemical corrosion on metal surfaces [29]. ...
The coefficient of friction between railway wheels and rails is crucial to railway operation and maintenance. Since the wheel–rail system is an open system, environmental conditions, such as humidity and temperature, affect the friction coefficient. Pin-on-disc testing was conducted to study the influence of environmental conditions and iron oxides on the coefficient of friction between the wheel and rail. The iron oxides were pre-created in a climate chamber. The surfaces of the tested samples were analysed using X-ray diffraction, scanning electron/focused ion beam microscopy, and Raman spectroscopy. Results indicate that the coefficient of friction decreases with increasing relative humidity (RH) up to a saturation level. Above this level, the coefficient of friction remains low and stable even when the RH increases. In particular, when the temperature is low, a small increase in the amount of water (i.e., absolute humidity) in the air can significantly reduce the coefficient of friction. At high humidity levels, a water molecule film can keep the generated haematite on the surfaces, counterbalancing the effect of rising humidity.
... When we limit the research to dry friction and aim to compare numerical and experimental results, we should consider what dry friction actually is, and whether and in what way it is possible to achieve ideally dry and clean metal surfaces without the influences of oxides and humidity [17,37,38]. It is remarkable that even an apparently trivial phenomenon, such as air humidity, can significantly affect the friction in joints [39,40], and thus, structural damping. Also, oxides and their formation time considerably influence the friction in mechanical connections [16,17,41]. ...
... As mentioned in Section 1, the coefficient of friction has a crucial role in the analysis of mechanical connections and it can strongly affect nonlinear structural response. For the friction between steel surfaces, the friction coefficient varies from 0.1 to 0.8 [15][16][17]24,[39][40][41]85]. This broad range of values is caused by a variety of parameters that influence friction, as discussed in Section 1. ...
The objective of this research is to develop a numerical model of one widely used bolted beam splice connection that dissipates energy through structural damping. The reference experimental setup is carefully designed to obtain the highly nonlinear dynamic response due to the suddenly released load. The fact that the monolithic beam with welded connection has a linear response is utilized for the initial calibration of the numerical and experimental models. Then, the numerical model of bolted beam splice connection is verified and adopted through an iterative process. The influences of time and spatial integration, bolt load application, element type, contact formulation, bulk viscosity, and mass scaling are discussed. A special attention is given to the load application and load release functions. After the verification, the Abaqus/Explicit numerical model is validated through the comparison with experimental data, where an appropriate friction coefficient is adopted. It is demonstrated that the nonlinear structural damping occurs due to the complex micro slip behavior at the contact interface.
... Then, the relative humidity is lowered by the increase of temperature. Delamination was the main wear mechanism at RT ( Fig. 4(a)), and there was a transition towards the combination of delamination and adhesive wear with decreasing relative humidity [20]. Additionally, decreasing the humidity could result in increasing the adhesive wear of stainless steel [21]. ...
... This explains the increased fretting wear of the plate sample above 200°C ( Fig. 10(a)). Consequently, a transfer layer occurred on wear scars at 200°C and 285°C (Fig. 5(d), Figs. 6 and 8(b)), was a barrier between the two contacting surfaces and was responsible of reducing surface interaction [20,21]. In addition, the maximum wear volume was reported to be largest at a particular humidity level in the fretting wear of pure nickel [22]. ...
Fretting wear tests of Inconel 690 alloy have been carried out at various temperatures (room temperature-RT, 90 °C, 200 °C and 285 °C) for tube/plate contact configuration. The worn surfaces and cross-sectional morphologies were observed through scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and electron probe microanalysis (EPMA). Moreover, a particular debris cleaning method was used to remove wear particles of worn Inconel 690 alloy effectively in order to estimate exact wear volume. Overall, the results indicated that temperature had a great impact on fretting wear behavior and wear mechanisms. With increase in temperature, the principal wear mechanisms changed from delamination wear to the combination of delamination and adhesive wear, as demonstrated by the presence of an adhesive transfer layer at 285 °C, instead of a compacted debris bed at 90 °C. The adhesive transfer layer seemed to protect the surfaces better due to a reduction in the interaction of the worn surfaces. Finally, higher friction coefficient and wear volume appeared at lower temperature (RT to 90 °C), compared to that associated with higher temperature (200 °C and 285 °C).
... One tribological process of interest in the life evaluation of machine elements is the fretting, which can be defined as a relative cyclic motion between two surfaces, with a non-uniform distribution of local relative displacement at their contact [1]. Depending on the loading conditions, material properties and environment, fretting can cause fretting wear, which combines all four basic mechanisms (oxidative, adhesive, surface fatigue and abrasive), or fretting fatigue, which combines surface and bulk fatigue [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Fretting wear and fatigue severely decrease the life of machine elements (e.g., rolling element bearings, screw and rivet assemblies, etc.) subjected to variable loading and vibration [10]. ...
... One observes that the mean wear rate displays a maximum w max at a certain relative humidity denoted RH max . Occurrence of RH max can be explained through the processes related to amount of oxygen and water adsorbed into the surface, in correlation with the adhesive wear [9][10][11][12][13][14][15][16][17]. For RH below RH max during a dry oxidative process, repeatedly formation and breakdown of the surface oxide film leads to generation of very small wear particles, which are not hard enough to produce abrasive wear, but acts as a lubricating powder to reduce the adhesive fretting wear. ...
Influence of the moist air humidity (10-70%) on the fretting characteristics of steels under grease lubrication is experimentally investigated. Ball (bearing steel, JIS SUJ2) on disk (carbon steel, JIS S15C) type fretting tests for 0-20 mg of grease supplied before each test at the punctual contact between ball and disk were conducted at 50 μm slip amplitude and 6.7 Hz frequency. From the shape of the friction hysteresis one calculates the slip index, and based on it, determines the type of fretting regime against the number of fretting cycles. Influence of the grease amount and relative humidity on the friction coefficient, slip index and wear rate is interpreted based on the occurrence of the grease film breakdown. Fretting wear rate appears as unaffected by variation of the environmental humidity for an amount of grease exceeding 3 mg, this representing the minimum amount necessary to avoid the grease film breakdown. Results obtained are useful to find the amount of grease necessary but sufficient for proper lubrication, and hence to protect the environment by grease saving. In order to generalize the results obtained for ball- bearings, screws, joints, guide-ways, etc., a tribological analysis based on the Stribeck curve was performed and then, the amount of grease necessary but sufficient to obtain fully lubricated fretting regime in moist air for ball bearings was discussed in detail.
... They have suggested that it is due to the reduction of the oxidation rate on the steel worn surface and to the formation of iron hydroxide and ferri-oxide-hydrate. These oxides and water adsorption act as protective layers that prevent the metal/metal interaction [13,14]. Goto and Buckley [15] found the opposite, which is a direct correlation between wear and humidity: the lack of oxygen adsorption in the presence of water vapour can reduce the rate of oxidation and thus increase the wear. ...
... In this case the surface temperature is widely lower than 500 1C and the total wear remains negative for the duration of the test. Some authors also suggest that the reduction of the oxidation rate is due to the formation of iron hydroxide and ferri-oxide-hydrate [13,14]. These oxides can act as protective layers preventing metal/ceramic interaction. ...
The friction and wear behaviour of a carbon steel in sliding contact with a plasma-sprayed ceramic coating (Cr2O3) is investigated under different conditions of normal load and relative humidity, through a pin-on-disk equipment. The samples are analysed by means of Optical Emission Spectroscopy (OES), Optical Microscope (OM), Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), surface roughness, fracture toughness and microhardness tester. The friction was continuously monitored during the tests while the wear rate of the coatings was evaluated by measuring the wear scar profiles after the tests. The wear rate of the pins was determined by weighing them before and after the wear tests. For all the normal loads applied in dry conditions, the metallic film transfer onto the ceramic surface was observed. In wet conditions, the metal transfer largely depended on the normal load applied. Microcracks were noticed along the splat and columnar grains boundaries on the Cr2O3 wear scars. The observations of the worn surfaces of the pins indicate a mild-oxidational wear mechanism with the appearance of ploughing and plastic deformation.
... The sliding-induced transformation from sp 3 diamond structure to sp 2 graphite structure reduces the Coefficient of Friction (COF) from 0.20 to 0.05 [5]. Some tribofilms are generated due to tribochemical reactions between the wear debris and oxygen or moisture [6]. ...
The utilization of anodized aluminum (Al) components would contribute greatly to combat against dry friction if good tribological properties could be attained. Despite its hardness, the wear rate of anodic coatings presents a major problem in many applications, including automotive, aerospace and high-tech industries. Recently, nanolayers of Ti demonstrated high tribological effectiveness and unusually low dry friction on anodic coatings. However, few researchers focus on the tribological characterization of nanolayers of other elements. In this study, nanolayers of Ti, Zr, Hf, Cu, Cr, Nb and Sn were deposited on anodized 1050 and 6082 alloys by magnetron sputtering and Atomic Layer Deposition. Major attention was devoted to surface roughness and hardness measurements, because of their importance for static friction. The results showed that structural, chemical and other intrinsic properties of nanolayers of Group IVB elements in many cases led to significant friction reduction, when compared to those of Cu, Cr and Hf. Nanolayers of 15 nm to 75 nm thicknesses appeared most effective tribologically, while 180 nm or thicker layers progressively lost their ability to sustain low dynamic friction. Deposition of nanoscale structures could provide advantages for the anodized Al industry in protection against incidental friction and wear.
... When we limit the research to dry friction and aim to compare numerical and experimental results, we should consider what dry friction actually is, and whether and in what way it is possible to achieve ideally dry and clean metal surfaces without the influences of oxides and humidity [17,37,38]. It is remarkable that even an apparently trivial phenomenon, such as air humidity, can significantly affect the friction in joints [39,40] and thus, structural damping. Also, oxides and their formation time considerably influence the friction in mechanical connections [16,17,41]. ...
... Wear is a system property and not a simple material characteristic, as frequently misconceived. It depends on the microstructure of the contacting materials [6], their relative motion (sliding, rolling etc.) [7], contact geometry [8], surface characteristics and topography [9], working conditions [10], environment [11] etc. In addition, a 'realistic' wear rate of some industrial components is much smaller than the one usually measured with conventional lab-scale tests. ...
With the increased attention to resources, sustainablity and reduction of carbon footprint on the life cycle of products, one of the challenging tribological issues is the prediction of long term wear. Indeed, in many industrial and technological components, materials operate under dry or lubricated conditions for thousands of hours. However, contrary to the determination of a coefficient of friction, which can typically reach ‘steady state conditions’ in a few hours, the determination of wear under realistic conditions is by definition a long term test. It is not easy to accelerate a wear mechanism without fundamentally changing it.
In addition, friction tests are more repeatable than wear tests and for this reason it is always necessary to run multiple repeat tests and obtain a reliable statistical result. Commonly, to characterise a single material couple under one set of test conditions, requires at least three repeats at one duration and ideally this is to be repeated for more than one test duration to plot also the evolution of wear.
It is clear that with a single-station test machine and tests that take weeks to perform, it is economically and practically impossible to generate enough measurements for data with high confidence levels. Therefore, in this work an approach is presented to measure the wear of materials is an efficient way and under realistic contact conditions. Such a method can be potentially used to more easily map wear evolution and performance of different materials.
... Thus, the wear debris formed at the room temperature could not provide a protective effect to the wheel and rail surfaces ( Fig. 14(a)), leading to high mass losses and severe surface cracks on wheel and rail rollers. Due to the lack of moisture being absorbed on the contact surfaces at the low temperature, the wear particles had a higher tendency to adhere to the wheel and rail surfaces [31]. Furthermore, finer ejected wear debris was observed ( Fig. 13(b)) at the low temperature, which was considered to be beneficial to the formation of a debris bed on the rubbing surface [32]. ...
In this study, the wear and damage behaviors of three heavy haul rail steels (including one hypereutectoid rail steel and two eutectoid rail steels) were investigated at room (around 20 °C) and low (-40 °C) temperatures using a rolling-sliding wear test machine. The results indicated that, compared with eutectoid steels, the hypereutectoid rail steel had a better wear resistance and a better rolling contact fatigue (RCF) resistance at the room temperature, and better wear resistance but worse RCF resistance at the low temperature. Compared with the room temperature, at the low temperature both the hypereutectoid and eutectoid rails had better wear resistance, the RCF resistance of eutectoid steels was improved but the RCF resistance of hypereutectoid rail was reduced. At the room temperature, the worn surfaces of both wheel and rail materials were dominated by surface cracks. On the contrary, at the low temperature, the worn surfaces of wheel and rail materials were dominated by third body layers (TBLs) and oxidized spots, respectively.
... However, the effect is lost even at low humidity [7]. Since most applications involving pure metal-metal contact use solid or liquid lubricants to reduce interfacial friction, [8][9][10], the tribological study of pure metal-metal interaction is studied less extensively [7]. Some research has been conducted to understand the effect of humidity on the friction of steel and aluminum [10][11][12]. ...
Tribology investigations were conducted to understand the effect of humidity and water adsorption at the interfacial surface on the friction coefficient of titanium. Pin-on-disk tribometer tests were conducted at different levels of humidity ranging from 0% to 71% RH using aluminum and steel pins on a titanium plate. The variation of the mean coefficient of friction was plotted as a function of relative humidity. The friction coefficient slightly decreased when the relative humidity was increased from 0% to 10% RH. However, it increased with a further increase in humidity. The maximum friction coefficients were observed at 55% and 65% RH for steel and aluminum, respectively. The thickness of the wear tracks also showed the same trend as the friction coefficient. Under high humidity conditions, water vapor can condense on the surface of the moving machine parts. To understand the influence of this water film, a pin-on-disk test was carried out on a sample where a thin film of water masks metal surfaces from contact. Although the coefficient of friction was similar for both the aluminum and steel pins’ interaction with titanium (~0.36), the wear tracks were not formed for steel pin/titanium interaction even though this experiment was conducted for more cycles.
... Particularly the effects of nanoparticles, present always on brake surfaces, were not addressed. Liew reported that the sliding wear of steel on steel contact increased by about 1.5 orders of magnitude when the relative humidity decreased from 80 to 28% [7]. Quite opposite trend was detected for wear rate of aluminum on aluminum contact where wear increased by about half an order of magnitude by increasing the relative humidity from 28 to 80%. ...
... 1.3) at a faster rate to form a boundary lubrication layer (Liu et al. , 2009). It has been reported that vapour can react with steel to form interfacial layers such as iron hydroxide and ferri-oxide-hydrates effective in reducing wear and friction (Liew 2006). Moisture can also adsorb physically on the worn surface and act in a protective manner so as to prevent direct contact between the surfaces (Goto and Buckley 1985). ...
Cutting fluids are widely used in most machining processes to produce superior surface finish and suppress tool wear. Due to the increasing cost associated with the procurement and disposal, and environmental issues of traditional cutting fluids, researches have been carried out to search for biodegradable lubricants and alternative lubrication methods to reduce the dependency on traditional cutting fluids. The growing demand for biodegradable lubricants has opened an avenue for using vegetable oils as alternative lubricants for machining. This chapter discusses the effectiveness of various types of biodegradable oils as lubricants and additives, and alternative lubrication methods such as minimum quantity lubrication (MQL), mist lubrication and solid lubrication in machining processes.
... 1.3) at a faster rate to form a boundary lubrication layer (Liu et al. , 2009). It has been reported that vapour can react with steel to form interfacial layers such as iron hydroxide and ferri-oxide-hydrates effective in reducing wear and friction (Liew 2006). Moisture can also adsorb physically on the worn surface and act in a protective manner so as to prevent direct contact between the surfaces (Goto and Buckley 1985). ...
The environmental and toxicity issues of conventional lubricants as well as their rising cost lead to renewed interest in the development of environmental friendly oils as lubricants and industrial fluids. This chapter provides a review of the fundamental research works carried out on tribotesters to investigate the effectiveness of vegetable oil in suppressing wear and frictional force. Results obtained in these studies are useful to explain the mechanism by which the vegetable oils reduce friction and tool wear in machining (Chap. 3). Intensive review of the previous works shows that vegetable oils have high potential to be used as lubricant and additive to replace conventional lubricants and additives.
... Fretting tests with an Al-Zn-Mg alloy found wear to increase with increasing RH due to the lack of adhered debris [37]. Similarly, pin-on-disk tests using BS1474 aluminum found an increase in wear as RH increased from 20% to 80% [38]. More debris was found on the 88 Friction 3(2): 85-114 (2015) pin at lower RH and the higher wear was attributed to debris egress. ...
Tribology involves not only two-body contacts of two solid materials—a substrate and a counter-surface; it often involves three-body contacts whether the third body is intentionally introduced or inevitably added during the sliding or rubbing. The intentionally added third body could be lubricant oil or engineered nano-material used to mitigate the friction and wear of the sliding contact. The inevitably added third body could be wear debris created from the substrate or the counter surface during sliding. Even in the absence of any solid third-body between the sliding surfaces, molecular adsorption of water or organic vapors from the surrounding environment can dramatically alter the friction and wear behavior of solid surfaces tested in the absence of lubricant oils. This review article covers the last case: the effects of molecular adsorption on sliding solid surfaces both inevitably occurring due to the ambient test and intentionally introduced as a solution for engineering problems. We will review how adsorbed molecules can change the course of wear and friction, as well as the mechanical and chemical behavior, of a wide range of materials under sliding conditions.
... The reason for their use is their thermal expansion, good tribological properties, good mechanical and physical characteristics and beneficial casting properties. Significantly good dimensional and thermal stability, resistance to corrosion and good heat conductivity are the factors which cause that the hypereutectic silumins are widely used in transport [4][5][6]. ...
The article presents the surface coarseness analysis for alloy AlSi17Cu5Mg coupled with cast-iron EN-GJL-350. Material after friction was tested in pin-on-disk system with the use of tribological tester T-01. Such coupling is in accordance with parameters applied in combustion engines. Analysis of coarseness allows to determine the influence of technological history on the parameters of material wear. It is important due to the fact of the proper choice of technology for manufacturing the materials applied in pistons of combustion engines. Tests were conducted in accordance with norm PN-ISO 4288:1988.
... The presence of adsorbed water due to the atmospheric humidity on the surface of a material can improve or deteriorate the tribological performances [6,7]. In some cases, the adsorbed water layer can be unfavorable and can expedite the tribological failures [8,9]. The presence of thin liquid films with a small contact angle at the interface can result in so-called liquid-mediated adhesion [10]. ...
A study was carried out on the influences of atmospheric humidity in the very early stage of sliding for austenitic stainless steel (JIS SUS316). Pin-on-disk tests were conducted under different rates of relative humidity (RH). A relatively low magnitude of applied load to lessen the influences of mechanical effect was employed for emphasizing the humidity effect on tribological phenomena. The results of the current study were compared with our previous study results obtained at higher magnitude of applied load. The comparison suggested different mechanisms of adsorbed water layer exert influences on the tribological phenomena in the very early stage of the sliding when applied load was changed.
... An analytical balance was used to measure the weight loss of the pin specimens to the nearest 0.1 mg. If the weight loss is not measureable, then the volumetric wear of pins was calculated as from the values of the scar diameter, assuming a perfectly hemisphere round tip [10]. This test equipment is traceable to national standards and each specimen was weighed three times to minimise the weighing error. ...
Wear in the railway wheel and rail contact is very closely related to the safety, maintenance and life cycle cost for the railway industry. An accurate prediction of wear is very important. Wear maps are commonly used as an input for simulating and predicting wheel/rail wear. These maps are often formulated for dry, unlubricated wheel/rail contacts at room temperature. In this study, wear maps were set up for different levels of humidity, contact pressure, sliding velocity and temperature, as well as with and without lubricant/oxide layers. Increasing the accuracy of wear maps requires separate maps for wheel tread/rail head and wheel flange/rail gauge contacts because there are significant differences in the contact conditions that cannot be included in a general wear map. The mild wear regime can be further divided into different areas instead of one constant wear coefficient as a result of environmental conditions and oxide layers.
... An analytical balance was used to measure the weight loss of the pin specimens to the nearest 0.1 mg. If the weight loss is not measureable, then the volumetric wear of pins was calculated as from the values of the scar diameter, assuming a perfectly hemisphere round tip [10]. This test equipment is traceable to national standards and each specimen was weighed three times to minimise the weighing error. ...
... Besides oxides on the powder particle surfaces, the formation of hydroxides and hydrated oxides should be considered. While oxide layers tend to be hard and brittle, hydroxide layers can assume a gel-like consistency with lubricating effects; these changes in the surface phases profoundly affect the wear behavior of metals [15]. It should be expected that the surface reactions and formation of hydroxides, as opposed to oxides, would also affect the flow of powders and possibly their agglomeration behavior. ...
Metal additive manufacturing has emerged as a new manufacturing option for aerospace and biomedical applications. The many challenges that surround this new manufacturing technology fall into several different categories. The paper addresses one of these categories, the physical mechanisms that control the additive manufacturing process. Physical mechanisms control the effects of processing parameters on microstructures and properties of additively manufactured parts. Some mechanisms might not have been recognized, yet, and for those that are currently known, detailed quantitative predictions have to be established. The physical mechanisms of metal additive manufacturing are firmly grounded in metallurgy, branching into laser physics and the physics of granular materials. Powder bed additive manufacturing is described from the powder storage to post-processing and elements of metallurgy are highlighted that are relevant for the different aspects of the additive manufacturing process. These elements include the surface reactions on powder particles, the heating and melting behavior of the powder bed, solidification, and post-processing. This overview of the different metallurgical aspects to additive manufacturing is intended to help guide research efforts and it will also serve as a snapshot of the current understanding of powder bed additive manufacturing.
... Olofsson and Sundvall [11] demonstrated that the coefficient of friction can be reduced from 0.65 at RH 40% to below 0.4 at RH 95% by using a pin-on-disc rig equipped with a climate chamber. Liew [12] reported a transition from high to low friction in the RH range of 50-60%. In addition, iron oxides are also inevitably involved in the wheelrail contact influencing the adhesion coefficient. ...
... 12 A transition occurring at low values of normal load or sliding velocity was called T 1 by Welsh 12 and has been observed by varying the surface roughness, 3 the atmospheric temperature, 14,15 the materials hardness 16 and the relative humidity. 17,18 In an earlier work, we found the T 1 transition from mild to severe wear when the hardness of the harder body was diminished. 5 This result showed that not only the hardness of the softer body influences the tribological behaviour but also the hardness of the harder body. ...
This paper aims to investigate the effect of varying the hardness of both sliding bodies on the operating wear regime. Unlubricated sliding wear tests were performed using a pin-on-disc configuration. The friction coefficient was monitored during the wear tests, and the variation of mass loss of bodies as a function of sliding distance was obtained to estimate the steady-state wear rate. The results showed that the operation of mild and severe wear regimes was influenced by the initial hardness of materials. Under the high pin hardness conditions, a decrease in the disc hardness promoted the severe wear regime operation prior to the action of a mild wear regime. Under the low pin hardness conditions, a severe wear regime was established. When the harder disc was tested, a mild wear regime was observed. Copyright © 2012 John Wiley & Sons, Ltd.
... Transitions are also found when other variables are changed. In particular, the T 1 transition has been observed with variation of surface roughness [4], atmospheric temperature [9,10], materials hardness [14,15] and relative humidity [16,17]. In brief, wear regime transition is such a complex phenomenon that any factor in the tribological system can have a fundamental role. ...
In the unlubricated sliding wear of steels the mild-severe and severe–mild wear transitions have long been investigated. The effect of system inputs such as normal load, sliding speed, environment humidity and temperature, material properties, among others, on those transitions have also been studied. Although transitions seem to be caused by microstructural changes, surfaces oxidation and work-hardening, some questions remain regarding the way each aspect is involved. Since the early studies in sliding wear, it has usually been assumed that only the material properties of the softer body influence the wear behavior of contacting surfaces. For example, the Archard equation involves only the hardness of the softer body, without considering the hardness of the harder body. This work aims to discuss the importance of the harder body hardness in determining the wear regime operation. For this, pin-on-disk wear tests were carried out, in which the disk material was always harder than the pin material. Variations of the friction force and vertical displacement of the pin were registered during the tests. A material characterization before and after tests was conducted using stereoscopy and scanning electron microscopy (SEM) methods, in addition to mass loss, surface roughness and microhardness measurements. The wear results confirmed the occurrence of a mild-severe wear transition when the disk hardness was decreased. The disk hardness to pin hardness ratio (Hd/Hp) was used as a criterion to establish the nature of surface contact deformation and to determine the wear regime transition. A predominantly elastic or plastic contact, characterized by Hd/Hp values higher or lower than one, results in a mild or severe wear regime operation, respectively.
To investigate the effect of erucamide on the tribological properties of GCr15 steel, polyurea grease is prepared with different concentration of erucamide as additive. The tribological behavior of erucamide on the surface of GCr15 steel is studied by reciprocating friction test. The results show that 1.5wt.% erucamide has the best tribological property and the friction-induced vibration and noise suppression capability, which is attributed to the formation of lubricating film on the transition region of the friction surface, which maintains the friction in a relatively stable state, and the maximum thickness of lubricating film is 3.91 μm.
Steel's friction and wear characteristics depend not only on the load applied and the nature of the contact surface but also on the environmental circumstances directly and indirectly. This research deals with an investigation of tribological behavior and the wear mechanism of low carbon steel and the effect of load (10 N–100 N), varying temperature (room temperature—200 °C), and relative humidity ranging between 30% and 70% under high-frequency reciprocating condition. Variation of wear rate and coefficient of friction with test parameters was evaluated by generating 3D surface and contour plots. Wear surface morphologies were also characterized. The synergistic effects of the parameters led to a very complex trend in the variation of wear rate and coefficient of friction. Due to the complexity of the problem, an artificial neural network was coupled with the genetic algorithm for the modeling and optimization of tribological characteristics. Simultaneous minimization of wear rate and coefficient of friction was obtained at 18.7349 N load, 199.99 °C temperature, and 49.8332% relative humidity. The worn surface comprised a low shear oxide film and pressed debris patches. The artificial neural network model was also obtained with a significantly high accuracy having an overall R-value close to 1 for both wear rate and coefficient of friction.
In this study, a twin-disc test rig with an environmental control chamber was used to conduct experiments on the influence of ambient temperature and humidity on the adhesion and damage of CL60 wheel steel. The results indicated that the degree of wheel surface oxidation increased with increasing temperature under high humidity conditions. The formation of iron hydroxide on the surface increased friction and damaged the surface. As the relative humidity increased, the moisture in the generated oxide debris reached a saturated state, and the debris exhibited a pasty texture that significantly reduced adhesion. Under high humidity conditions, the plastic deformation layer of the wheel increased obviously. The depths and lengths of cracks that formed in the wheel under high humidity conditions were greater than those produced under medium and low humidity conditions.
The friction coefficient of a specific material combination is often assumed to be invariant, even in manufacturing processes, such as during the tightening of threaded fastener joints. This paper considers the impact of storage conditions on threaded fastener friction. Fasteners were stored in hot humid and sub-zero temperature conditions to study friction in the thread and under-head contacts. Four Zn-flake coatings, commonly used in the automotive industry were considered. Consequent tightening of these fasteners at room temperature revealed that storage history had a significant impact on their friction coefficients, halving under-head friction in some cases. This varied behaviour was considered to be a response to coating nano-hardness and structure and differences in adsorption/absorption of water and zinc-oxide formation during storage.
To serve in a corrosive environment, a corrosion-resistant rail steel U68CuCr has been developed in China. In the present study, the wear behavior of U68CuCr was investigated and compared with the commonly used rail steel U71MnG by rolling contact friction tests. The results indicate that the mass loss and wear rate of U68CuCr are smaller than those of U71MnG. The wear rates under the dry condition are smaller than those under the water–oil condition. In addition, the formation of oxide and spalling finally achieves the dynamic equilibrium on the surface of two types of rail steels. However, the duration of the lubricative and protective wear debris layer is longer for U68CuCr. Moreover, the worn surface of U68CuCr is relatively flat, while the wear regime of U71MnG is more severe. The amount and volume of the spalling pits of U68CuCr are smaller. Furthermore, the plastic deformation layers are shallower, and the rolling contact fatigue cracks are shorter for U68CuCr because of the finer pearlitic microstructure. The results prove that the U68CuCr rail steel shows good wear-resistant ability, suggesting its superior suitability for application in high-speed railways in a marine environment.
A wheel/rail system is an open system, where the operating environment factors, such as atmospheric humidity, temperature, and oxidation behavior, are subject to change. This study conducts experiments on a twin-disc test rig with a climate chamber to examine the effect of ambient humidity on adhesion and damage between the wheel and rail interface under hot weather conditions. Results indicate that humidity has a remarkable effect on the adhesion behavior of a wheel–rail rolling contact interface. Under low humidity levels, fatigue wear is predominant, abrasive wear becomes increasingly serious with an increase in humidity, oxide wear debris acts as abrasive particles and accelerates the wear process. Under high humidity levels, a friction-reducing layer is formed, and the rollers are protected from excessive wear. Adhesive wear is the main damage mechanism in addition to oxidative wear. Raising the humidity level helps the rollers to avoid excessive wear. However, high humidity level is unconducive to the safe operation of trains because high humidity and a high heat environment promotes the formation of tribochemical products which are a mixture of iron oxide and water molecules and lead to a great decrease in the adhesion between wheel and rail.
The tribological and conductive properties of current-carrying rolling pairs were investigated in humid air and water drops. As the environment changes from a very low RH atmosphere (10% relative humidity) to liquid water, current-carrying friction coefficient increased from 0.14 to 1.03. It is speculated that current-induced adhesion, meniscus force and current-induced meniscus force can provide additional friction force. With the increasing of the friction coefficient, the wear mechanism current-carrying pairs transforms from adhesive and abrasive wear to severe fatigue wear. When water changes from a gaseous state to a liquid state, the form of fatigue changes from scale to spalling because of pressurization effect. X-ray photoelectron spectroscopy (XPS) analysis shows that water is advantageous to tribo-oxidation and electrochemical oxidation, resulting in the formation of CuO. The weakening effect of oxidation on the electrical conductivity can be illustrated by contact resistance and conductive atomic force microscopy (CAFM) map. The paper reported the mechanical and chemical effects on the current-carrying contact pairs in wet conditions, which could be very helpful in understanding on water-involved surface damage and oxidation.
Aerospace and automotive grade steels are often coated with sacrificial coatings to mitigate corrosion and increase service life. Some of these coated components are subjected to sliding motion and, for these cases, a sacrificial Cd coating provides the additional benefit of a low shear strength, essentially acting as a solid lubricant. Cd coatings will be replaced due to their toxicity and Al coatings are a candidate with low hardness that could replace Cd for these applications. In this study, a linear reciprocating sliding test is used to measure the wear and friction coefficient with change in relative humidity, with and without Cd and Al sacrificial coatings. These soft coatings do not offer much wear resistance, so the study focuses on how the substrate wears after coating removal compared to uncoated substrates (grit-blasted and as-rolled steel). Two types of Al coatings deposited by aprotic and ion vapor process and a low hydrogen embrittling (LHE) Cd coating were studied. An order of magnitude difference in wear rate of the steel substrate was observed with changes in relative humidity and type of coating. For example, wear rate of steel substrate in dry air decreases from ∼3x10⁻⁴ mm³/N·m to 3x10⁻⁵ mm³/N·m when Cd coating is applied. Whereas, wear rate of steel substrate increases to ∼1.5x10⁻³ mm³/N·m with Al coating. Application of LHE Cd coating decreases the substrate wear irrespective of relative humidity, but IVD Al is only effective during high relative humidity of 60%. Electrodeposited Al coating, irrespective of relative humidity, aggravates substrate wear. After the coating has been worn through, residual third bodies, which were oxides and hydroxides of the coating, affect the wear process of the steel substrate.
Carbon alloyed transition metal dichalcogenide (TMD) coatings have attracted attention in the field of tribology due to their ability to provide friction and wear reduction in diverse operating environments. This study is devoted to the up-scaling of the deposition process for self-lubricant molybdenum-selenium-carbon coatings. For this purpose, Mo-Se-C nanocomposite coatings are deposited by closed-field unbalanced magnetron sputtering in a semi-industrial deposition unit. The effect of the addition of carbon to sputtered MoSex coatings, the usage of negative substrate bias, and the target-to-substrate distance are studied. The carbon addition significantly improves the compactness and the mechanical properties of the pure MoSex coatings. An additional improvement is achieved by the usage of negative substrate bias during the deposition. The optimized coatings have featureless cross-sectional morphology and amorphous X-ray diffraction structure. Transmission electron microscopy reveals the presence of nanosized crystallites of MoSe2 enclosed in an amorphous carbon matrix. The hardness, measured through nanoindentation, is ~7–8 GPa for the coatings having C content of ~50 at.%, and a compact morphology. The best tribological properties for reciprocating pin-on-disk testing are characterized by coefficients of friction of 0.08–0.09 in ambient air conditions and 0.04–0.06 in dry N2 environment and elevated temperature (200 °C). The lowest specific wear rates were 2–3 × 10⁻⁷ mm³/Nm during sliding in ambient air and under dry N2, with higher values of 7–10 × 10⁻⁷ mm³/Nm during testing at elevated temperature. Mo-Se-C coatings can be upscaled for industrial production showing potential tribological properties for low friction applications.
The influence of relative humidity on friction and wear is subject of several studies in the last decades. A comprehensive understanding of physical and chemical phenomena affecting the tribology is hampered by the lack of reproducible experimental results, by the large number of variables, and by several difficulties in the detection of tribochemical processes and products.
In the present work, we analyze the wear coefficient and the wear volumes of 686 unlubricated tests performed on different oscillating tribometers with 100Cr6 balls on 100Cr6 planes at different relative humidity.
Aim of this work is to assess the repeatability and reproducibility of data, to determine the dependence of the wear coefficient on the relative humidity, to understand the underlying physicochemical phenomena and to build three dimensional maps of the wear coefficient as a function of both humidity and the product of normal force and sliding distance.
Air, oxygen and nitrogen are examples of environmental friendly lubricants in the gaseous state. Even at low pressures, they have strong influences on the cutting performance. However, as the cutting speed increases, the effectiveness of the gas lubricants attenuated. This has conventionally been attributed to the reduction in interface penetration and thus of intimate contact and adhesion between chip and tool. This chapter also provides a review of the advanced techniques supplying gaseous and vapours capable of prolonging tool life at high cutting speeds.
Various grades of fuels are used in automobiles, as a result the engine components are continuously subjected to simultaneous action of corrosion and wear. Ni-SiC composite coating is the most widely investigated and commercialized wear-resistant coating in the automotive industry. However, this coating cannot be used at temperatures above 450 °C due to the tendency of SiC to react with Ni and form brittle silicides. An alternate approach is to use oxide-reinforced coatings. In the present study, zirconia, ZrO2 and, yttria-stabilized zirconia, YSZ-reinforced Ni composite coatings have been developed by electrodeposition method. It was observed from the microhardness studies that there is no significant difference in the values for Ni-SiC and Ni-ZrO2 coatings. The corrosion behavior was evaluated using polarization and electrochemical impedance studies. The studies showed that oxide particle-reinforced Ni coatings possessed better corrosion resistance due to their lower corrosion current density, I
corr. Tribo-corrosion studies were carried out to understand the synergistic effect of wear and corrosion on the performance of Ni-based composite coatings in 0.5 M Na2SO4. Among various composite coatings, Ni-YSZ exhibited less material loss thereby showing better tribo-corrosion behavior.
Triological behavior of 1.08%C steel under temperature range of -55°C-20°C and dry friction was investigated using a tribometer with ball-on-disk configuration. The counterbody was ψ3 mm GCr15 steel ball. The normal load was 0.5 N-2.5 N and the sliding velocity was 0.319 m/s. Worn surface on the 1.08%C steel was observed by SEM. Chemical composition of the debris was analysised by EDS and XPS. Hardness of the worn surfaces was measured. Friction coefficient below 0°C was obviously higher than that of 20°C. Drop of temperature obviously aggravated the wear of 1.08%C steel. Analysis on tribochemical reaction indicates that weakened oxidation of wear debris with drop of temperature was an important reason for aggravation of wear. Decrease of oxide in the debris increased adhesion between the two metals.
The surface of 50CrMo4 (German) steel ball screw was induction quenched, and then tempered at low temperature. The phase constitution, microstructure, microhardness, residual austenite content in quenched layer of the steel were analyzed. Moreover, the wear characteristics of quenched layer under dry friction condition and different loads were investigated. Results reveal that the microhardness of the quenched layer increases from 250 HV to 700 HV and the microstructure is mainly composed of fine tempered martensite. The fracture morphology from the surface to matrix is intergranular fracture, dimple and transgranular fracture, and dimple fracture respectively. Furthermore, the friction coefficient decreases with increasing friction load. At the low load the grooves are observed in the wear surface and the wear mechanism is abrasive wear. With the increasing of friction load some pits begin to appear on the wear surface, and the number of it is increasing. However, at the high load, deep grooves and large flakes are observed, the wear mechanism is the mixture of serious abrasion and delamination. ©, 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.
Aluminum disk was slid against silicon carbide (SiC) pin, SUS 440 C stainless steel pin and aluminum pin in distilled water to evaluate lubrication compatibility. The friction and wear behavior of aluminum disk was influenced by the pin material. The both wear of disk and pin of aluminum/SiC pair, aluminum/SUS 440 C stainless steel pair and aluminum/aluminum pair increased in that order. Friction of aluminum/SiC pair, aluminum/aluminum pair and aluminum/SUS 440 C stainless steel pair increased in that order. In all pairs, tribo-oxidation took place on the aluminum disk surface during sliding in water and the resulting aluminum oxide deposited on the sliding surfaces. In the case of aluminum/SiC pair and aluminum/SUS 440 C stainless steel pair, the aluminum oxide inhibited aluminum adhesion to SiC pin and SUS 440 C stainless steel pin effectively and abraded the disk and pin surfaces. On the other hand, severe adhesive wear took place on the sliding surfaces of aluminum/aluminum pair.
In this article, the high-speed dry sliding tribological behaviors of CrNiMo steel against brass in nitrogen and oxygen atmospheres are investigated using a pin-on-disc tribometer. The worn surface is characterized by scanning electron microscopy and electron dispersion spectrums analysis. The wear mechanisms of CrNiMo steel are also analyzed. The results indicate that the tribological properties of CrNiMo steel are coincidental with the law of dry sliding of metal, where the friction coefficients decreases with an increase in sliding speed and with normal load. However, the atmosphere has obvious effects on the tribological properties of CrNiMo steel. In the sliding process, friction heat plays an important role on the tribological properties of materials in high-speed dry friction. The high-speed wear mechanism of CrNiMo steel varies at different atmospheres. In a nitrogen atmosphere, the wear mechanism of CrNiMo steel is mainly characterized by adhesion at a lower speed and load. When the speed and load are increased, melting trace is found in the worn surface accompanied by an abrasive wear. In an oxygen atmosphere, the mechanism is characterized by adhesion at a lower speed and load; with an increase in speed and load, it gradually transformed into oxidation wear and abrasive wear. The difference of the wear mechanisms in the different atmospheres and test parameters is primarily due to the transfer films formed on the contact surfaces of the sliding pairs. In our experimental conditions, the surface film is mainly the metal film in nitrogen, whereas, it is the oxide film in oxygen.
The lubricity of a selection of multicomponent fuels and pure substances was measured on a high frequency reciprocating rig at different vapor pressures. The objective was to evaluate the effect of air humidity on the wear scar diameter. Specific correction factors depending on the chemical composition of the fuel are proposed to normalize the mean wear scar diameter. The humidity correction factor recommended by the European standard shows an overestimation for most of test fuels, except biodiesel fuels which require higher correction factor. The effect of the water content in the fuel on the wear scar was also studied, showing significant direct correlations for all test fuels. An indirect approach for the estimation of the fuel hygroscopy, based on the combination of the effects of humidity and water content of the fuel on the wear scar, has confirmed that the air humidity affects wear through the humidification of the fuel. The results obtained by the proposed method show that paraffinic fuels are more hydrophilic than diesel fuels but they are less hydrophilic than biodiesel and alcohol fuels, which is consistent with the literature.
The effect of water vapor on the friction and wear between copper and 440C stainless steel was studied using a ball-on-flat tribometer, polarization-modulation reflection–absorption infrared spectroscopy, and Auger electron spectroscopy. The wear behavior changed drastically as the relative humidity (RH) varied in inert gas (nitrogen or argon). In a dry environment, a small degree of abrasive wear of soft copper was observed. In the RH range of 10–70 %, catastrophic adhesive wear of the soft copper surface was dominant. A high RH (>80 %) environment exhibited wear of the hard 440C stainless steel surface and the steel wear debris was deposited onto the copper. The adsorption isotherm measurements for copper and stainless steel revealed that water adsorption increases quickly between zero and 10 % RH and then the adsorption proceeds more slowly as RH increases further. The adsorbed water layer thickness increases rapidly again as saturation is approached. It seems that the thin layer of adsorbed water under 70 % RH facilitates the adhesive wear through passivation of grain boundaries or acceleration of crack propagations, but the thick water layer formed over 80 % RH acts as an electrolyte medium allowing galvanic corrosion to commence.
In order to clarify the influence of temperature below freezing point on the tribo-oxidation of steel–steel friction pairs, tribological behaviour of certain steel from −55 °C to 20 °C was investigated using a ball-on-disk tribometer in a thermotank which could provide environment with constant temperature and humidity. The counterbody was a 3 mm GCr15 steel ball. The normal load was 0.5 ∼ 2.5 N and the sliding velocity was 0.319 m/s. Worn surface on the steel, wear scar on the steel ball and wear debris were observed and analysed by SEM and EDS. It was found that the friction coefficient presents a sudden increase when the ambient temperature drop from 20 to − 10 °C. This is caused by decrease of relative humidity. The friction coefficient maintains the same value when the temperature change is between − 10 and −55 °C. A drop of temperature from 20 to −55 °C aggravated wear of the steel. Analysis on tribochemical reaction process indicates gradually weakened oxidation of wear debris along with a drop of temperature should account for the aggravation of wear. Furthermore, along with the drop in temperature, the worn surface became rougher and more structure fractures were formed on the friction track, which led to more severe abrasive wear of the steel. Drop of temperature increased abrasive wear but decreased adhesive wear. Copyright © 2008 John Wiley & Sons, Ltd.
Purpose
The purpose of this paper is to study the friction and wear properties of CrNiMo steel pin against brass disk in different oxygen fractions. CrNiMo steel is currently widely used in industry and military fields for its excellent performance in some severe environments. The atmosphere and temperature are key factors affecting the wear behaviors of CrNiMo steel. The study aims to make better use of CrNiMo steel in different atmospheres.
Design/methodology/approach
Friction and wear experiments were conducted using a pin‐on‐disk tribometer equipped in an atmosphere controllable chamber. The chamber allows switch between vacuum and gas mixtures of N2 and O2. The oxygen content was managed by magnetic coupling flow meter. The sliding speed of 1, 2, 3, 4 m/s and the applied sliding contact load of 5, 6.5, 8, 9.5 N were used in friction test. In order to obtain information on the wear mechanisms, the worn surface of the pin was examined by scanning electron microscopy and energy dispersive X‐ray spectroscopy.
Findings
A close dependence is clearly shown of the friction and wear on the content of oxygen gas in elevated temperature. Increasing the content of oxygen in the atmosphere under higher normal load condition is beneficial to friction reduction of the steel/brass pair. Different wear mechanisms were found with a transition from the adhesive wear in nitrogen, to a mixed adhesion and oxidation wear when increasing the content of the oxygen in the atmosphere.
Originality/value
This paper provides a reference for the similar steel used in severe environments.
In order to reduce frictional resistance between archwire and bracket during orthodontic tooth movement, carbon nitride (CNx) thin films were deposited on the surface of archwires with ion beam assisted deposition (IBAD). The energy-dispersive X-ray spectrometer (EDS) analysis showed that the CNx film was successfully deposited on the surface of the orthodontic wires. X-ray photoelectron spectroscopy (XPS) analysis suggested that the deposited CNx film was sp2 carbon dominated structures, and diversiform bonds (NC, NC, et al.) coexisted in the film. The friction tests indicated that the CNx film significantly reduced the wire-bracket friction both in ambient air and in artificial saliva. The sp2C rich structure of the CNx film as well as its protection function for the archwire was responsible for the low friction of the wire-bracket sliding system.
The sliding behavior of high purity aluminum was investigated, with a focus on the chemical composition and structure of wear debris generated in different environments. Sliding tests were carried out with a pin-on-disk tribometer. The pin was a 440 C stainless steel ball and the disk was 99.99% aluminum. Relative humidity in air varied from 20% to 95%. The sliding behavior depended strongly on the test environment, especially the relative humidity. Wear debris was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The debris from air tests differed both chemically and structurally from the original contacting material. A high concentration of oxygen was detected by EDS in the wear debris and on the wear track. XPS was employed to gather information on the bonding of the oxygen incorporated with aluminum during sliding. XRD analysis suggests that the metallic component of the wear debris produced in air retains high elastic strains. Weight changes of the wear debris during heat treatment were measured by TGA and these tests suggest that the debris includes hydroxide. The endothermic reaction detected by DSC provides evidence for the loss of water during heating. The results provide new information about tribochemical phenomena during the sliding of aluminum. These involve more than simply forming and removing a film of Al2O3.
The mechanical behavior and failure mechanisms of non-conductive adhesive (NCA) joints exposed to accelerated testing environments have been investigated. The study reveals that moisture preconditioning induces a rapid and drastic decrease in the mechanical strength and modulus of NCA joints. Recovery experiments indicate that the loss in modulus was reversible upon re-drying, but nonetheless more irreversible damage did occur at NCA joints due to hydrolysis. A hydrolytic degradation mechanism at the NCA/polyimide interface is proposed.
Nano-ceramic composite coatings were prepared by the electrodeposition method using sulphamate electrolyte. Nickel was chosen as the metal matrix and nano-Cr2O3 particles were chosen as the reinforcement. The surface morphology and the particle distribution in the coating were analysed using field emission scanning electron microscope (FESEM). The particle content was obtained using energy dispersive X-ray analysis (EDAX). A change in the surface morphology of Ni was seen on the incorporation of Cr2O3 particles. The coatings were characterized for their structure and no change in the diffraction pattern was seen between plain Ni and Ni-Cr2O3 composite. The mechanical property like microhardness and tribological behaviour of the nano-composite coatings was studied and it was observed that the incorporation of Cr2O3 particles enhanced the mechanical properties of Ni matrix. The nano-composites were analysed for their thermal stability and corrosion resistance. An improvement in thermal stability was observed but no change in the corrosion behaviour of Ni was seen on the incorporation of nano chromium oxide particles.
To study the behavior of adhered fragments on rubbing surfaces, the transverse movement of a slider is measured and recorded during the wear process. The gap between the mating surfaces is enlarged gradually through the origin and growth of a transfer particle adhering to the slider and then closed suddenly by the removal of the particle. The removal process of wear particles can be observed by an optical microscope. Furthermore, an X-ray microanalysis is made on the cut section of the rubbing system just before the removal of the particle. The particle is press-slide flattened in shape and has a hair line mixed structure containing metals of both mating surfaces.
Since 1994, white spot syndrome virus (WSSV) has been detected in cultured shrimp Penaeus monodon in Peninsular Malaysia. The gross signs, target organs and histo-cytopathology for the viral infection were studied and it was found to infect most organs and tissues including oocytes, but not hepatopancreatocytes and epithelial cells of the midgut, which were regarded as refractory tissues. Based on a time-sequence of ultrastructural cytopathology, 4 cytopathic profiles and 6 phases of viral morphogenesis were described. The virions were elliptical to short rods with trilamilar envelopes that measured 305 +/- 30 x 127 +/- 11 nm. Viral nucleosomes were often present singly in infected nuclei and were associated with the early stages of viral replication. The structure of WSSV pathognomonic white, cuticular lesions was examined at the microscopic and ultrastructural levels and the mechanism of their formation appeared to be related to the disruption of exudate transfer from epithelial cells to the cuticle via cuticular pore canals.
The friction and wear behaviour of 100Cr6–100Cr6 was investigated in a ball-on-flat arrangement for the situation of unlubricated oscillating sliding motion at room temperature. The relative humidity (RH) inside the test chamber was varied in the range from 3% to 100%. The coefficient of friction is only slightly influenced by the humidity, whereas the wear increases drastically if the humidity is decreased below 15%. In a medium RH range the oscillating sliding tests show a good repeatability of friction and wear data with standard deviations smaller than ± 10%.
Humidity and temperature have played an important role in the wear of materials in general and particularly cast iron and steel. In this paper we present experimental results on the wear of steel depending on a variety of humidities under various temperatures (this is part of the tribology programme in Vietnam). The experimental results also have been compared with the wear of the materials in working conditions.
The tribological properties of a ultra-fine AISI 304 austenitic stainless steels obtained by means of a martensitic transformation and subsequent austenite reversion are reported. The effects of the grain size on the wear resistance of such material is, for the first time, investigated as a function of the atmospheric humidity. Decrease of relative humidity in wear tests of AISI 304 steel produces an increase in weight loss and in the friction coefficient. A beneficial effect of grain refining is also shown with respect to large grain steel in that the finer grain steel produces less initial weight loss and the weight loss with an increase in the humidity is also less pronounced.
In Korea, the atmospheric air humidity varies between 30% and 90% with the seasons. Thus the study of the effect of humidity on the behavior of wear is important in predicting the seasonal wear for tools and dies. This paper presents the effect of atmospheric air humidity on the wear of carbon steels for un-lubricated pin-on-disc sliding contact under constant load and speed.In this study, it was found that at low humidity severe wear occurs and at a high humidity mild wear can be expected. In addition, the humidity effect on the transition from mild to severe wear and vice versa is related strongly to the carbon concentration of the steel. Experiments were carried out in a chamber where the humidity was maintained accurately by a humidifier. To investigate the relationship between the carbon concentration in a steel and the wear behavior, three different carbon steels, i.e. 1020 steel, 1041 steel and 1045 steel were used.
The wear of a wide range of material combinations has been studied in unlubricated conditions. Loads of 50 g to 10 Kg and speeds of 2 to 660 cm/s have been used. A representative selection of the results is given. As a broad classification two contrasting mechanisms of wear have been observed. In nearly all experiments, and for all types of wear mechanism, once equilibrium surface conditions are established the wear rate is independent of the apparent area of contact. The wear rate is accurately proportional to the load for only a limited number of combinations but there are many other examples for which the relation between wear rate and load shows only a small deviation from direct proportionality. It is suggested that with the same surface conditions the wear rate is proportional to the load; in practice this simple relation is modified because the surface conditions depend on the load. These rules of wear may be derived, on a priori grounds, from the experimental results, or from more detailed theoretical calculations.
The pattern of wear outlined in part I is interpreted in the light of further experiments which reveal that the change from severe wear to mild is governed by the hardness and state of oxidation of the surfaces. At light loads (< T1) severe wear is inhibited by the combined effects of strain hardening and oxidation. At higher loads (> T2) mild wear recurs primarily as a consequence of a change of phase induced by frictional heating. The hardness accompanying the phase change is great enough, initially, to suppress severe wear without the intervention of an oxide film. At loads immediately above T2, however, the hardness tends to fall if rubbing is prolonged and oxidation is again essential to preserve the mild wear state. Sustained phase-hardening does not occur until a higher load, roughly coinciding with the T3 transition, is attained and this finding has an important bearing on the influence of inert atmospheres. The onset of permanent hardening is not responsible for the divergent pin and ring wear rates at T3, though the phenomena may be linked by the magnitude of the temperatures required to cause phase-hardening; the T3 transition and the trend at higher loads have been identified as special effects associated with the thermal asymmetry of the rubbing system.
The broad trends of the wear rate when steels rub together without lubrication have been studied by means of pin and ring apparatus. Over a wide range of load (10 g to 40 Kg) and sliding speed (1\cdot 7 to 266 cm/s) the wear process at equilibrium is either of a severe type, producing coarse metallic debris, or of a mild type, producing fine oxidized debris. The corresponding wear rates differ by more than two orders of magnitude. Transitions from one wear process to the other occur at well-defined loads and for soft steels a basic pattern, comprising three transitions, has been identified: T1, a change from mild wear to severe at light loads; T2, a change from severe wear back to mild at higher loads; T3, a minor change in the mild wear rate at loads above T2, characterized by divergent wear rates of the pin and ring. The way in which this pattern varies with the sliding speed and with the composition and hardness of the steel is traced and the findings of previous investigations co-ordinated in the general framework.
Research conducted on steels is motivated by a technological need to further improve their properties. Among the different steel types, austenitic stainless steels possess good corrosion resistance and formability. However, they also have a relatively low yield strength. One way of increasing the yield strength is by grain refining. This work presents a study on the effect of relative humidity and applied load range on the friction and wear of AISI 304 austenitic stainless steel characterized by two different grain sizes: 2.5 and 40 m. Using a precision microtribometer, with applied loads in the N regime, it was found that capillarity plays a dominant role. At the same loads, in high humidity environments, both the fine and coarse grain steels exhibit high friction relative to measurements performed under dry conditions. At loads greater than 2 mN a reversal in microfrictional behavior occurs in that microfriction was greater under dry conditions than under moist conditions. At loads of 2 N, using a standard ball-on-disk tribometer, severe wear was evident at low humidities while relatively lower wear was observed at high humidities indicating a lubricating effect of water.
Fretting fatigue tests of a carbon steel and an aluminum alloy were carried out in various environments and the effects of oxygen and water vapor were investigated by tangential force measurements, the initiation and propagation of cracks and hardness and structural changes of the damaged surface layer. With carbon steel the effect of water vapor is negligible but oxygen has a deleterious effect on the initiation and propagation of fretting fatigue cracks. However, with an aluminum alloy the effect of oxygen is small but water vapor accelerates the initiation and propagation of cracks. Environmental effects are more dominant than the stress conditions with an aluminum alloy; material softening and structural change of the surface layer occur.
An investigation was conducted to determine the effect of water vapour content in air on the frictional behaviour during fretting of pure metals: iron, aluminium, copper, silver, chromium, titanium and nickel. The fretting experiments were carried out under various humidity levels, ranging from dry air to 50% relative humidity at 23°C. During the experiment the frictional force between fretting surfaces was measured. Pure metals, except iron, were found to have a maximum value of the coefficient of friction during the steady-fretting stage (μs) at a specific humidity (RHmax). Iron showed a rapid decrease in μs with increasing humidity at RHmax. Each pure metal also exhibited maximum fretting wear at RHmax. The value of μs at RHmax for each metal was strongly related to the heat of formation of the lower metal oxide, indicating that the adhesive contact area was larger at RHmax for the fretting of metals with less chemical activity. At high humidity levels water vapour generally reduced the coefficient of friction, μs.
Pin-on-disc experiments were carried out to produce both oxidative and metallic wear. Measurement of the temperature rise of the aluminium wear pins and calculations based on these results show that the temperatures are too low to account for the oxide produced during wear.Oxidation during wear occurs by a two-stage process of oxidation of asperities followed by fracture and compaction into the valleys on the metal surface. As the oxide layer increases in thickness it also becomes smoother and the wear rate remains relatively low.
The fundamental mechanisms of sliding wear postulated by the delamination theory of wear are reviewed in terms of the experimental and analytical work done to date at MIT. Each of the rate determining processes involved in delamination wear, i.e. plastic deformation of the surface layer, crack nucleation and crack propagation, is discussed for various metals with different microstructures. The effects of sliding speed, lubricants and complex loading on wear are also discussed. A hypothesis (without experimental verification) is advanced for the formation of the Beilby layer. Various dislocation mechanisms that might be responsible for the “dislocation depleted layer” are considered.
An investigation was conducted to determine the effect of oxygen and water vapour on the friction and wear behaviour of an Al-Zn-Mg alloy under fretting conditions. Fretting wear experiments were carried out in wet air, dry air and in dry argon. In this case the peak-to-peak relative slip amplitude was varied from 20 to 260 μm to determine the critical slip amplitude of fretting wear in these environments.The experimental results indicated that the wear rates in dry air and in dry argon under macroslip conditions were almost the same and quite lower than the wear rate in wet air. This revealed that the effect of oxygen on fretting wear was not large but that water vapour accelerated the fretting wear of the aluminium alloy. The cyclically softened material due to overaging was observed below the contact surface during fretting in wet air. The mechanism involved rapid fretting wear in wet air which caused the removal of a heavily work-hardened layer as it was formed but the softened material below it was not removed.
The wear mechanisms and their transitions of 52100 and 1080 steels with various microstructures in dry sliding were systematically studied by wear testing and SEM observations of worn surfaces and wear particles. The results show that there are three dominant wear mechanisms, i.e., mild wear characterized by oxidation, severe wear characterized by adhesion and delamination, and melting wear, appeared in succession with increasing normal load and/or speed. The transition of wear mechanisms depends mainly upon the conditions of testing. The microstructure of steels have almost no remarkable effect on the general law of the transition of wear mechanisms. On the basis of calculating the wear rate and analyzing the morphology of worn surfaces and wear particles, a criterion was suggested, by which one can easily identify the transition from mild wear to severe wear.
The wear mechanisms of steel 1080 and the wear behaviour of various microstructures in the steel were systematically studied by wear testing, and by SEM and TEM observations of worn surface and wear particles. The experimental results show that three dominant wear mechanisms appeared in succession with increasing normal load and/or speed during unlubricated sliding. The transitions of the wear mechanisms depend mainly upon the conditions of testing, and changes in microstructure of the steel have no marked effect on the transitions. In the case of oxidation-dominated mild wear, no obvious differences in wear volume were found for the various microstructures. However, considerable differences in the wear volumes were observed under the condition of severe wear characterized by adhesion and delamination and the wear resistance of the different microstructures increased in the order: spheroidized carbide, martensite, bainite and lamellar pearlite.The experimental results also indicate that the differences in wear resistance of the various microstructures were caused by the differences in microstructural thermal stability, resistance to plastic deformation, resistance to nucleation and propagation of microcracks and especially by the differences in energy consumption in these layers during wear.
Pin-on-disk type wear tests of mild steel in contact with itself were conducted under unlubricated conditions in moist air to investigate the effect of changes in load on the transition behavior between severe and mild wear. Machines in operation are usually subjected to varying loads. In this study, two contact load levels were used as a simple varying load condition. The load was changed in a step-wise manner between the low and high levels either once or twice during certain tests.Severe wear appears at the high load levels and mild wear at the low load levels in wear tests under constant loading. After oxidized, work-hardened wear surfaces have been formed under mild wear at the low load during the first stage, the wear mode changes to “quasi-mild wear” having a low rate at the high load in the final stage. The load range, where the low wear rate can be maintained under quasi-mild wear, extends to the higher load level after the change(s) in load. Once the quasi-mild wear surface has been generated, the wear mode can be maintained even at the high load for a very long sliding distance.
A new theory for wear of metals is considered. The theory is based on the behavior of dislocations at the surface, sub-surface crack and void formation, and subsequent joining of cracks by shear deformation of the surface. The proposed theory predicts qualitatively that the wear particle shape is likely to be thin flake-like sheets and that the surface layer can undergo large plastic deformation. It also predicts a number of experimentally observed phenomena such as the difference in wear particle sizes and the dependence of fretting wear rate on displacement amplitude. All theoretical predictions are supported by experimental evidences. A wear equation is developed based on the proposed theory.
Wear processes in general are influenced by the surrounding atmosphere, humidity especially. For fretting wear several authors have examined the influence of humidity on the wear scar morphology, the wear volume and the composition of the wear debris. No agreement between the different results has been found, yet. In the present study, the influence of the humidity in the ambient air on the fretting process is examined. The friction, the wear volume and material transfer are measured for the fretting of a bearing steel ball against a flat steel specimen under gross-slip regime, in running-in as well as steady state conditions. The wear and material transfer are quantitatively measured with Thin Layer Activation method. It has been observed that high ambient humidity inhibits adhesion and accompanying material transfer. As a result, high humidity has a beneficial influence on fretting wear, in opposition to generally accepted hypothesis.
Reduction of adhesive forces and friction of iron polycrystals in vacuum by chemisorbed films
Friction and wear of machine parts-Surface heat treatments for increase wear resistance
- Takaeuchi
E. Takaeuchi, Friction and wear of machine parts-Surface heat treatments for increase wear resistance, Mach. Tools 23 (1979) 68-74.