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Performance of reactively co-sputtered titanium chromium nitride films in artificial saliva: Corrosion protection and reduction in the release of potentially toxic elements
Abstract
Having been deposited on 304 stainless steel (SS304) substrates by RF reactive co-sputtering, 1 μm-thick Ti-Cr-N films were annealed at 400 °C and 700 °C. Accordingly, nitride phases of TiN and CrN, and as a result of the lost capability as an oxygen diffusion barrier, oxide phases of Fe₂O₃, Cr₂O₃, and TiO₂ formed after the annealing process at 700 °C. For short-term immersion (1 h), the corrosion testing illustrated that the film annealed at 400 °C shows greater corrosion resistance than the other films and SS304. For long-term immersion (30 days), all the films demonstrated greater corrosion resistance than SS304, with the as-deposited film delivering the best performance. It was found that protective passivation layer formation, porosity closures, and surface characteristics such as pits, trenches, grooves, cracks, and protuberances govern the corrosion behavior differences. The surface micrographs imply that pitting corrosion and superficial filiform corrosion are among the underlying mechanisms affecting the surfaces. Finally, given the concerns about the capability of SS304 to release toxic elements such as chromium, it was determined that not only can Ti-Cr-N films increase the corrosion resistance of SS304 but also they can reduce the release of chromium by almost 67% in the long-term exposure.
In this study, the authors propose a procedure to enhance pure Ni-Al powders through graphene oxide dispersion in water for plasma spraying. The enhanced powders were utilized to coat A36 steel via plasma spraying. Next, the powders and the coatings were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, micro-Raman spectroscopy, and field emission scanning electron microscopy. Given the capability of the generated X-ray to characterize near surfaces to a depth of a few micrometers, the performed X-ray microanalyses convey that the carbon species incorporated within the powders through the graphene oxide dispersion can act as nanofillers reducing the number of holes/pores in the plasma-sprayed coatings. Potentiodynamic polarization testing and electrochemical impedance spectroscopy were used to investigate the corrosion behavior of the samples at two intervals: after 1 h and after 30 days of exposure to a 3.5% NaCl solution. According to the results of the corrosion testing, the enhanced coatings can display about 2.35 times lower corrosion current density compared to pure Ni-Al coatings, with the corrosion potentials of the enhanced coatings being higher than that of pure Ni-Al coatings (i.e., improved corrosion resistance). This improvement in corrosion resistance is also evident when the enhanced coatings are compared to the A36 substrate after 30 days of exposure to the solution. It appears that the incorporated carbon nanofillers, by reducing deep holes and pores that communicate with the surface of the substrate, ultimately determine the highest corrosion resistance. Thus, the outcome offers enhanced Ni-Al coatings possessing superior anticorrosion properties that typical plasma-sprayed Ni-Al bond coats may not exhibit.
Au–Ag–Pd alloys are extensively applied in dentistry due to their excellent mechanical properties, high corrosion resistance, and biocompatibility. This research carried out to determine the effect of pre-annealing on electrochemical corrosion by using electrochemical techniques such as open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). The Au50Ag25Pd25 alloy samples were annealed at 750 °C, 800 °C, and 900 °C. It was observed that as the pre-annealing temperature rises, the corrosion resistance steadily decreases because of the chemical inhomogeneity on the sample surfaces. Comparing the non-annealed sample (SN) to pre-annealed samples (S3, S5, and S7), potentiodynamic polarization parameters show that the SN has a higher polarization resistance and a lower corrosion current density. Imaging from scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) reveals that the sample surface forms oxide films that become thinner with increase in pre-annealing temperature. These results provide insight into the behavior of corrosion of Au–Ag–Pd alloys and can help optimize their performance in dental applications.
Magnetron sputtering is a very versatile technique extensively employed for the deposition/growth of thin films. However, the deposition of desirable magnetic films is one of the challenges confronting magnetron sputtering owing to the shunting of magnetic flux by magnetic targets in conventional magnetron sputtering equipment. This flux shunting culminates in lower plasma density, non-uniform plasma confinement, and uneven erosion of magnetic targets, adversely affecting the growing films’ thickness uniformity and chemical homogeneity—the latter can be particularly serious in magnetron co-sputtering. In this article, it is discussed that these issues can be avoided by cylindrical sputtering. As for planar sputtering, formerly offered technical solutions including the utilization of thin foils as magnetic targets, the deployment of gapped targets somewhat allowing the magnetic flux of the magnetron assembly, the employment of a target heating system increasing a magnetic target’s temperature greater than or equal to its Curie temperature, facing target sputtering, magnetron sputtering assisted by coupled plasma inductively generated in an internal coil, and the generation of plasma remotely from magnetic targets (i.e., high target utilization sputtering) are scrutinized with their advantages/disadvantages being further examined. Finally, it is discussed that not only can auxiliary grid deployment mitigate/remove the issues of planar magnetron sputtering by modifying spatial plasma density distribution near the target but also it can solely shoulder the responsibility of ionization enhancement and plasma confinement for deposition of magnetic films.
Surface coating technology is an important way to improve the properties of orthodontic appliances, allowing for reduced friction, antibacterial properties, and enhanced corrosion resistance. It improves treatment efficiency, reduces side effects, and increases the safety and durability of orthodontic appliances. Existing functional coatings are prepared with suitable additional layers on the surface of the substrate to achieve the abovementioned modifications, and commonly used materials mainly include metal and metallic compound materials, carbon-based materials, polymers, and bioactive materials. In addition to single-use materials, metal-metal or metal-nonmetal materials can be combined. Methods of coating preparation include, but are not limited to, physical vapor deposition (PVD), chemical deposition, sol-gel dip coating, etc., with a variety of different conditions for preparing the coatings. In the reviewed studies, a wide variety of surface coatings were found to be effective. However, the present coating materials have not yet achieved a perfect combination of these three functions, and their safety and durability need further verification. This paper reviews and summarizes the effectiveness, advantages and disadvantages, and clinical perspectives of different coating materials for orthodontic appliances in terms of friction reduction, antibacterial properties, and enhanced corrosion resistance, and discusses more possibilities for follow-up studies as well as for clinical applications in detail.
The influence of hydrogen level on compressive properties of TC21 alloy processed by thermohydrogen treatment (THT) at 1123 K was studied through room-temperature compression experiments. The microstructures of TC21 alloy processed by THT at 1123 K were investigated by OM, XRD, and TEM. Results showed that hydrogen level affected apparently the microstructures and compressive properties of TC21 alloy processed by THT at 1123 K. With increasing level of hydrogen, the yield strength of TC21 alloy decreased to a minimum initially and then increased; the deformation limit of TC21 alloy decreased slightly to a minimum first, then increased to a maximum, and ultimately decreased. At a hydrogen level of 0.78 wt%, the deformation limit of TC21 alloy was the highest among all THT-processed TC21 alloys and showed an increase of 244.33% compared with the original TC21 alloy.
The corrosion resistance and antibacterial activity of dental metal materials are important service performances. In this paper, the TiN and Ti-N-O coatings with different chemical compositions were deposited on Ti6Al4V alloy by physical vapor deposition (PVD). The phase structure, surface morphology and elemental distribution of the Ti-N-O coatings were characterized by XRD, XPS, SEM and EPMA. The electrochemical corrosion behavior of the Ti-N-O coatings in acidic and fluoride-containing artificial saliva was investigated. The antibacterial activity of the coated Ti alloy was evaluated by an in vitro antibacterial test. The results show that with increasing O2 flow rate in the reaction atmosphere, the phase compositions of the Ti-N-O coatings gradually change from TiN to TiNxOy, Ti2O3, TiO2 and Ti3O5. The Ti-N-O coatings show good passivation behavior. Particularly, when the ratio of N2 and O2 flow rate is 2:1, the corrosion current density of the Ti-N-O coated specimen in acid (pH = 5.2) solution is only 6.0 × 10⁻⁸ A/cm². In an acidic solution containing 0.1% NaF, the passivation potential of the Ti-N-O coatings exceeds +1.0 V, and the corrosion resistance is exceeds that of a TiN coating. When the ratio of N2 and O2 flow rate is 1:1, the antibacterial rate of the Ti-N-O coating against Staphylococcus aureus approaches 90%.
In this paper, the incorporation of auxiliary grids/electrodes into the design of the sputtering method is scrutinized by studying the impact of factors such as grid size, grid position, grid bias voltage, electrode sheath design, substrate bias voltage, reactive gas partial pressure, and magnetic trap configuration on the discharge condition and thin-film growth. In this regard, utilizing the updated Berg model for reactive sputtering, the authors obtained a formulation for the reactive grid-assisted sputtering. By the newly-developed formulation, the sputtering rate and the reactive gas partial pressure were simulated as a function of the reactive gas flow rate for various grid-to-target distances, argon partial pressures (0.67, 1.6, and 3.6 Pa), and discharge current densities (0.01, 0.015, and 0.02 A/cm2). According to the computation results, with a grid being utilized, the width of the hysteresis loops can be modified in a broader range by changing either the grid-to-target distance, the argon partial pressure, or the discharge current, resulting in better control over the deposition process. Moreover, the novel configuration of anode-spot-assisted sputtering was proposed to significantly ionize sputtered/neutral atoms near the substrate and to simultaneously deposit sputtered species and products produced as the direct result of introducing dust into the dense plasma. Finally, diverse configurations of the grid-assisted co-sputtering method were introduced for two prime purposes: deposition of composite films in any desired ratios of constituents without significantly changing the other co-sputtering parameters, and favorable alternation of a hysteresis loop for one of the guns at shared gas flow rates.
Stress-shielding and loosening compromise the success of dental implants under real-life service conditions. This work evaluates the mechanical behavior of superficially modified porous titanium dental implants fabricated by two different routes: conventional powder-metallurgy and space-holder techniques. A novel, feasible and repetitive protocol of micro-milling of the implant thread (before sintering), as well as surface modification treatments (after sintering) are also implemented. The discussion is conducted in terms of the influence of porosity and surface roughness on the stiffness and yield strength of implants. The macro-pores concentrate stress locally, and, at the same time, they could act as a barrier to the propagation of micro-cracks. Higher rugosity was observed for virgin implants obtained with spacer particles. Concerning superficially modified implants, while bioglass 1393 was the most effective coating due to its greater infiltration and adhesion capacity, chemical etching could improve osteoblast adhesion because modifies the roughness of the implant surface.
Corrosion is an inevitable problem, which causes a significant burden to any country's economy. It is making research imperative to reduce the economical loses that are resulted due to corrosion. As remedial measure, various techniques and materials have been utilized. Fortunately, metal/metal oxide nanoparticles (NPs) were proved beneficial to augment the corrosion resistance against various harsh environments. Therefore, metal/metal oxide NPs have attracted attention to exploring the corrosion inhibition efficiency with different coating systems. Furthermore, the mechanism of corrosion protection is also noteworthy to elucidate and categorize on the basis of distinguished inhibiting property offered by metal/metal oxide NPs. Literature is well consulted to describe the important factors affecting the corrosion inhibition efficiency of metal/metal oxide NPs.
Elastomeric ligatures are increasingly used as a part of esthetic orthodontic treatment, particularly in children. The aim of the present study was to experimentally test whether these appliances may contribute to exposure to toxic elements. In the present study, elastomeric ligatures (ELs) were incubated in artificial human saliva for 1 month (a typical period of their use) and the release of 21 metals (Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mg, Mo, Ni, Pb, Rb, Tl, Ti, Sb, Sr, Sn, Zn, U, V) and 2 metalloids (As and Ge) was studied using inductively coupled plasma-mass spectrometry. For comparison, stainless steel ligatures (SLs) were incubated for 1, 3, and 6 months (since sometimes their use is prolonged) under similar conditions. The determined metal levels were compared to the corresponding safety limits for human exposure. During 1 month, the ELs released Cd, Co, Cr, Mn, Ni, and Sn at total mean ± SD level of 0.31 ± 0.09, 0.98 ± 0.30, 3.96 ± 1.31, 14.7 ± 8.5, 13.8 ± 4.8, and 49.5 ± 27.7 μg, respectively. Other elements were always below the detection limits. In case of SL, the release of Co, Cr, Fe, Ni, Mn, and Sn was observed, and the determined values increased over the studied period. After 6 months, their total mean ± SD levels amounted to 28.6 ± 0.2, 21.7 ± 0.2, 623.5 ± 3.0, 1152.7 ± 1.8, 5.5 ± 0.3, and 22.6 ± 0.2 μg, respectively. The released metal levels from both ligature types were always below safety limits. The release of Ni from SL during 6 months would constitute 5.0 and 11.5% of tolerable intake in adults and children, respectively. The results of this in vitro study highlight that the use of ligatures in orthodontic treatment can be considered safe in terms of metal exposure although elastic ligatures replaced on a monthly basis appear to be advantageous in comparison to the prolonged use of stainless steel appliances.
Extremely thin, Al–Zn–O composite films (21 ± 6 nm) are deposited on fused silica substrates under various percentages of oxygen in the oxygen/argon gas mixture (3%, 4.5%, 6%, and 7.5%). The films are prepared by a cylindrical DC magnetron sputtering system, utilizing a single compound target. The effects of the oxygen percentage on the compositional, morphological, and optical properties of the films are investigated by energy‐dispersive X‐ray spectroscopy, scanning electron microscopy, UV‐visible spectrophotometry, and atomic force microscopy. The chemical composition of the films is Al1 Zn1+X O with 0.2 < X < 1. The average visible transmittance of 93.6% with a high level of uniformity is obtained when the sputtering deposition performs under the oxygen percentage of 6%. It is found that the optical band gap of the films can be tailored toward higher energy by increasing oxygen percentage; however, the adjustable range is not so significant. The results offer cost‐efficient films with high, uniform transmittance in the visible region and with an ability to attenuate more than 10% of incident UV‐B radiation (280‐315 nm). This type of films can potentially be included in greenhouse screen systems to effectively protect the plants from the elevated UV‐B radiation without altering natural conditions.
All materials can suffer from environmental degradation; the rate and extent of degradation depend on the details of the material composition and structure as well as the environment. The corrosion of silicate glasses, crystalline ceramics, and metals, particularly as related to nuclear waste forms, has received a lot of attention. The corrosion phenomena and mechanisms of these materials are different, but also have many similarities. This review compares and contrasts the mechanisms of environmental degradation of glass, crystalline ceramics, and metals, with the goal of identifying commonalities that can seed synergistic activities and advance the current knowledge in each area.
Nanostructured Titanium chromium nitride (TiCrN) thin films at different pulsed frequencies were grown on steels by pulsed reactive DC magnetron sputtering technique. Thecrystal structure and morphology of the TiCrN films sputtered at different frequencies were characterized. The surface composition and chemical states of each element in TiCrN thin films were studied by ion scattering spectroscopy (ISS) and X-ray photon spectroscopy (XPS).The electrochemical corrosion behavior of the coated steels was monitored by both impedance spectroscopy and potentiodynamic polarization technique in 3.5% NaCl at room temperature. A block on ring wear tester was used to monitor the variation of coefficient of friction with different sputtering frequency. The mechanical applications of TiCrN thin films were studied by fabricating the thin films on micro drill bits and testing it on 1 mm thick steel plates. A superior surface finish, diameter precision of the hole, reduced material build up on the cutting edges and finally increased tool life were obtained with TiCrN coated HSS drill bits. Machining tests were conducted by coating the inserts with TiCrN thin films.
This work deals with localized electrochemical impedance spectroscopy (LEIS) which is an improved technique of the commonly used electrochemical impedance spectroscopy (EIS). Thanks to modern structural solutions, the LEIS technique ensures local impedance measurement. Therefore, it is used in the research into point corrosion, such as the pitting corrosion, and in the research into protective coatings or into alloys including alloy steels. This review paper presents the basic theory and the usability of the LEIS based on the literature on the newest research in the field of corrosion.
Dental implant systems are subject to failure in the screw connection part which can occur due to screw loosening or fracture. For solving the problem of loosening, some researchers had carried out the TiN(titanium nitride) and WC(tungsten carbide) coating on the abutment screw, while fatigue failure may still be not researched as an issue of coating materials. In this study, fatigue test was performed to estimate the fatigue fracture of coated abutment screw for implant system according to the ISO 14801. For this purpose, TiN and WC film coating was carried out on the abutment screw using EB-PVD and sputtering, respectively. For the fatigue test, the implant fixture and abutment were tightened to a torque 32Ncm using digital torque gauge with 0.1Ncm accuracy. Each prepared samples were fixed to uniaxial sinusoidal cyclic loading machine (ADT-AV01k1, Shimadzu, Japan) under load control between 42-420N and 58-580N. Fractured surface was observed with FE-SEM and EDS. The fatigue life of implant system used TiN and WC coated abutment screw was found to be relatively longer compared to non-coated abutment screw at 420N. Also, fatigue life of TiN coated sample showed longer than that of other samples at 580N. After the fatigue test at 420N, fatigue striations were showed on the fractured surface of non-coated abutment screw. The semi-cleavage surface was mainly observed on the TiN coated surface. Fatigue striations were regularly appeared at crack propagation step with striation thickness of 0.5 ㎛/cycle.
In the last decade, different methods have been developed for the determination of chromium(VI) concentration in water. These
methods use high cost equipment or they require a long preparation time. Because of their drawbacks, this paper describes
an on-line, rapid and sensitive procedure for the determination of Cr(VI) concentrations in aqueous solutions via pH and absorption
measurements. Only four Cr(VI) species are considered. The effects of pH and of total amount of chromium on the Cr(VI) speciation
are investigated. The molar absorptivities of four chromium species at 371 nm are determined by minimising an objective function.
The knowledge of these molar absorptivities and the measurements of pH and absorption at 371 nm lead to a rapid determination
of total Cr(VI) concentration. The reliability and applicability of the method were confirmed using synthetic water samples.
SUS 304 stainless steels have been widely used in orthodontics and implants such as archwires, brackets, and screws. The purpose of present study was to investigate the biocompatibility of both the commercial microcrystalline biomedical 304 stainless steel (microcrystalline 304ss) and novel-fabricated nanocrystalline 304 stainless steel (nanocrystalline 304ss).
Bulk nanocrystalline 304ss sheets had been successfully prepared by microcrystalline 304ss plates using severe rolling technique. The electrochemical corrosion and ion release behavior immersion in artificial saliva were measured to evaluate the property of biocorrosion in oral environment. The cell lines of murine and human cell lines from oral and endothelial environment were co-cultured with extracts to evaluate the cytotoxicity and provide referential evidence in vivo.
The polarization resistance trials indicated that nanocrystalline 304ss is more corrosion resistant than the microcrystalline 304ss in oral-like environment with higher corrosion potential, and the amount of toxic ions released into solution after immersion is lower than that of the microcrystalline 304ss and the daily dietary intake level. The cytotoxicity results also elucidated that nanocrystalline 304ss is biologically compatible in vitro, even better than that of microcrystalline 304ss.
Based on the much higher mechanical and physical performances, nanocrystalline 304ss with enhanced biocorrosion property, well-behaved in vitro cytocompatibility can be a promising alternative in orthodontics and fixation fields in oral cavity.
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Objective
Failure of dental implants treatment is frequently the result of bacterial colonization of implants followed by diseases like peri-implantitis. Recent studies have been made regarding the surface treatment of implants components, namely abutments that are in the interface of the living tissue with the implant. This work aimed at evaluating the antimicrobial profile of a silane-based coating with TiO2 adapted to an abutment screw, that was also developed as an anti-loosening agent, to prevent adhesion and migration of Gram + and Gram-bacteria, Staphylococcus aureus, and Escherichia coli, respectively.
Methods
Direct contact antimicrobial studies were conducted on coated and uncoated samples by resazurin fluorescent assay and cytotoxicity assessment was done via MTT indirect method on days 1 and 4. Sterilizations studies by FTIR analysis were also performed to understand the ideal balance between sterilization efficacy and coating functionality subjecting the samples to ethylene oxide, gamma irradiation, and autoclave sterilization, before antimicrobial testing. The implant system as a whole was also studied for its ability to block bacterial migration and preventing microleakage as well as an assessment of initial bacterial adhesion evaluated by scanning electron microscopy.
Results
Direct contact studies performed on coated samples showed a very high antimicrobial activity, while cytotoxicity assays revealed the coating to be safe and non-leachable. Sterilizations studies showed that the antimicrobial features of the coating were preserved and interchangeable regardless of the sterilization method. The implant system migration studies demonstrated that the implant system works as an efficient barrier for the studied bacteria.
Significance
The acquired results clearly show that it is possible to obtain a highly functional coating with obvious and marked antimicrobial features that together with an abutment that prevents bacterial migration and versatility in sterilization methodology has a very high potential in the dental implant field.
Nano-multilayer architecture based on physical vapor deposition is a promising way to tailor the structural and mechanical properties of nitride hard coatings for cutting tool applications. In this work, the mechanical and tribological properties of TiSiN/TiAlN coatings with different modulation geometry, namely modulation period, Λ, and modulation ratio, λ, were elaborated. The TiSiN/TiAlN nano-multilayer with reduced Λ of 8.5 nm and λ of 1:2.3 (thickness ratio of TiAlN to TiSiN sublayer) shows a noticeable increase in hardness to 36.8 GPa. The modulation geometry impacts the wear behavior of TiSiN/TiAlN nano-multilayers through two aspects. Firstly, the mechanical enhancement effectively promotes the wear resistance of coatings at room temperature. Secondly, the chemical variation changes the wear mechanism at high temperatures. For the situation at 600 °C, the combined action of adhesive, abrasive, and oxidative wear gives rise to dispersive and small oxide patches, adhered to sliding surfaces for TiSiN/TiAlN coatings with higher λ of, for instance, 2.3:1. This tribolayer contributes to the lower wear volume loss than the case at room temperature for the TiSiN/TiAlN with a Λ of 29 nm and a λ of 2.3:1. In contrast, the TiSiN/TiAlN coating with a lower λ of 1:2.3 exhibits mild abrasive and oxidative wear at 600 °C.
This work concerns high Al-containing TixAl1-xN coatings prepared using low pressure-chemical vapour deposition (LP-CVD). The coatings were examined using electron microscopy techniques, such as scanning transmission electron microscopy (STEM), energy dispersive X-ray analysis (EDX) and transmission Kikuchi diffraction (TKD). An intermediate TiN-layer with a 〈211〉 texture consisting of twinned, needle-shaped grains influences the subsequent growth of the TiAlN layer. The TiAlN grains were columnar with a texture of 〈211〉. As the grains grow along 〈111〉, with {001} facets, this led to a tilted pyramid surface morphology. The grains developed an internal periodic epitaxial nanolamella structure. The thicknesses were 2 nm for the low (x = 0.6) and 6 nm for the high (x = 0.9) Al-containing lamellae. The TiAlN layer growth could be described by a “two-wing” model, where two TiAlN grains with a twin-related orientation grow on a twinned TiN grain, where the two TiAlN grains gradually switch sides, making the appearance of two wings of columnar grains. In general, this work shows that it should be possible to control the growth of TiAlN layers by controlling the texture and morphology of an intermediate layer, such as TiN.
Amorphous Si–C-based (a-SiC) thin films as protective coating have attracting more and more attentions. But there are contradictory reports in the literature about the effect of sputtering power on the structural and mechanical properties of a-SiC films. Here, the influence of sputtering power on structural and mechanical properties of a-SiC thin films deposited by pulsed magnetron sputtering have been investigated. The results show that as-prepared films have a columnar structure and cauliflower-like pattern at lower sputtering power (100 W). Increasing the sputtering power from 100 W to 180 W, the columnar feature disappears and the thin films become denser. Meanwhile, the density of Si–C bond increases and the sp³/sp² radio decreases. The hardness (H) and elastic modulus (E) of the a-SiC thin films increase when the sputtering power increases from 100 to 120 W and then their almost keep constant when the sputtering power increases from 120 to 140 W. Further increases in sputtering power, the H and E increase again. The maximum H and E are about 20.2 GPa and 223.1 GPa at 180 W, respectively. Reason for excellent mechanical property is proposed in combination with the theory analysis and experiment results.
In modern dentistry, various techniques are being used to enhance longevity of a tooth implant. Among the most attractive solutions to promote the long-term stability of a dental implant, is the application of a protective coating on selected parts of the assembly.
In this paper, the use of 3-(glycidyloxypropyl)trimethoxysilane and tetraethyl orthosilicate (GPTMS/TEOS) sol-gel coating containing TiO2 nanoparticles is proposed as a locking agent to improve long-term stability of a dental implant. The concept is based on an approach used in machine industry, i.e. enhancing the frictional engagement between the mating parts and therefore preventing their unintentional loosening.
Compared with samples not subjected to surface modification, the proposed coating is effective in terms of improving the anti-loosening properties of the abutment screw. High locking efficacy of the sol-gel film, as well as its anti-wear performance, are achieved by the advantageous mechanical properties of the coating. Compared with a pure GPTMS/TEOS matrix, the incorporation of TiO2 NPs in the polymeric backbone results in an improvement of the resistance to hydrolytic degradation, as well as reduction of hardness and Young modulus of the coating.
Diamond-like carbon (DLC) coatings have been extensively studied over the last two decades in the field of materials engineering. The addition of effective bactericidal agents like silver suggests the potential application of silver-doped DLC coatings in the biomedical sector. In this paper, DLC coatings containing about 2 at. % Ag were grown on CoCrMo substrates by pulsed filtered cathodic arc co-deposition using pure graphite and silver targets. Morphology, structure and chemical composition of the coatings were characterized by SEM, XPS, XRD, Raman and HRTEM. Wettability and surface free energy were also measured. Mechanical properties were analyzed by means of nanoindentation and Rockwell-C adhesion tests. Corrosion resistance of coated and uncoated samples was determined by potentio-dynamic polarization tests in Hank's solution. Cytotoxicity and antibacterial activity against S. aureus and P. aeruginosa were also studied. For comparative purposes, nitrogen-doped DLC coatings obtained by RF magnetron sputtering were also prepared and characterized. Well-adhered and corrosion resistant Ag-DLC nanostructured coatings of up to 1.5 microns thick and 21 GPa in hardness were obtained. The doping concentration of silver studied in this work seems to be optimal for the preparation of non-cytotoxic coatings with a significant bactericidal activity.
Objectives
The aim of this study was to investigate the effect of the nanostructured hydroxyapatite (NHAp) and titanium dioxide nanoparticles (NTiO2) on dispersion in an adhesive containing monomers of Dipenta erythritol penta-acrylate monophosphate (PENTA) and Urethane dimethacrylate (UDMA), as well as evaluating the structural, optical and mechanical behavior of the composite material for dental aesthetic application.
Methods
The NHAp powders were synthesized through the wet chemical methods of hydrothermal and ultrasound-assisted precipitation. The microstructure, morphology and composition analysis of the powder of NHAp and NTiO2 were performed by scanning and transmission electron microscopy. The optical microscopic identification of the different colors was obtained due to varying the amounts of NHAp and NTiO2 in the adhesive. On the other hand, the diffuse reflectance spectra of the coatings were evaluated every 2 nm with the wavelength from 400 to 800 nm for combined specular and diffuse reflectance. The nanomechanical properties of the aesthetic coating such as (H), elastic modulus (E) and nanoscratching were evaluated by nanoindentation. The roughness of the composite coatings were evaluated by AFM.
Results
From different powders combinations, NHAP 75%Wt-NTiO2 %25 Wt, at (10Wt %) into a dental adhesive, the resulting mixture manifested the optimum aesthetic white appearance. The scanning and transmission electron microscopy images confirmed that the HAp nanorods and TiO2 nanoparticles sized were 55 nm and 20 nm respectively prepared by the high-energy ball mixed process. The values of nanomechanical properties of the optimum aesthetic coating were hardness, H = 3.2 ± 0.3 GPa, elastic modulus, E = 78 ± 3 GPa, Yield point, Y = 107 MPa ± 2 and scratching, maximum wear track deformation 3.7 ± 0.12 μm². The percentage of reflectance to optimum aesthetic white appearance was of 46.83% at 423 nm of wavelength.
Conclusions
The nanocomposite PENTA/UDMA with mixtures of Nanohydroxyapatite and titanium dioxide may be considerate as a mechanical toughened, also an option to modify shade qualities for dental aesthetic applications.
Abstract
Objective
To develop an antimicrobial and anti-adherent thymol (TOH)-containing coating on titanium (Ti) by a bioinspired one-step biocompatible method.
Methods
A nanolayer of adsorbed TOH (TOH-NL-Ti) was formed by an easy deep coating method on Ti surface. The treatment consists in a simple one-step immersion process in a TOH-containing solution. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), potentiodynamic electrochemical technique, open circuit potential records, Atomic Force Microscopy (AFM) and measurements of TOH release were used to characterize TOH-NL-Ti. Live/Dead staining and plate counting were employed to quantify attached and living adhered bacteria, respectively. Biocompatibility and cytotoxicity in fibroblastic and pre-osteoblastic cell lines were evaluated by acridine orange staining and MTT assay, respectively.
Results
TOH adsorbed on TOH-NL-Ti was detected by ATR-FTIR and electrochemical techniques. ATR-FTIR results showed that TOH nanofilms development involves spontaneous production of ketonic structures on Ti surface. AFM analysis revealed that the thickness of the TOH-NL was below 80 nm. Finally, microbiological assays confirmed that TOH-NL-Ti can inhibit the adhesion and kill attached bacteria leading to the eradication of leaving cells on its surface. After 24 h of biocidal release, the antimicrobial effect is also significant (a decrease of 3 orders in the number of attached bacteria).
Significance
The formation of TOH-NL-Ti nanolayer is a simple strategy able to be applied by not specially trained personnel, to reduce implant infection risks, ensure highly effective antimicrobial action and inhibition of bacterial adhesion on Ti surfaces without showing toxic effects for pre-osteoblastic and fibroblastic cells.
We have explored the features of coatings deposited by electron-beam evaporation of ceramic targets with different elemental composition in the fore-vacuum pressure range. The mass-to-charge composition of the beam-plasma formed, and the composition and characteristics of the coatings deposited by evaporation of ceramic targets of various different compositions have been investigated. The influence of target material elemental composition on the parameters of coatings deposited on a titanium substrate are assessed, including elemental composition, surface profile, microhardness, and Young's modulus.
Titanium (Ti) is widely used in dental implants; however, the bioinert surface has been shown to limit osseointegration, particularly in patients with poor bone quality. This study created a thin bioactive oxide film on Ti dental implants via oxygen plasma immersion ion implantation (OPIII) to improve bone cell differentiation and osseointegration. OPIII treatment was performed using low (10¹⁶ ions/cm²) and high (4 × 10¹⁷ ions/cm²) doses of oxygen ions. The Ti surfaces were characterized in terms of topography, wettability, chemical composition, and crystal structure. The differentiation of human bone marrow mesenchymal stem cells on OPIII-treated Ti surfaces was evaluated in vitro in terms of alkaline phosphatase (ALP) activity (early stage marker) and von Kossa staining (late stage marker). The osseointegration of OPIII-treated screw-type Ti dental implants in the femur of rabbits was evaluated in vivo using scanning electron microscope/backscattered electron imaging and histological staining at 4 weeks after implantation. OPIII treatment could induce a Ti oxide film on Ti surface without altering the surface topography, roughness or wettability. Higher oxygen ions dose increased the thickness of the surface Ti oxide film as well as the proportion of rutile phase titanium dioxide (TiO2) in the Ti oxide film. The OPIII-treated Ti surfaces presented higher ALP expression level, stronger von Kossa staining signal, and higher bone-to-implant contact. Note that all of these effects were more pronounced on surfaces created using higher oxygen ions dose due to the higher proportion of rutile phase TiO2. Overall, our results indicate that OPIII treatment using higher oxygen ions dose can enhance the in vitro bone cell differentiation and in vivo osseointegration of Ti dental implants.
The mechanical behavior plays a key role in the long-term stability of dental implants. The loosening of abutment screws is one of the most common problems. Plasma nitriding treatment (PNT) is a recently developed method of in situ surface modification to solve the screw loosening problem. In this study, we investigated the effect of plasma nitriding on the dental implant abutment screw joint. Abutment screws were treated with plasma nitriding. The preload force and friction coefficient of the screw were measured. The single fracture load (SFL) test and dynamic fatigue life (DFL) test were performed to test the fatigue performance of the implant screw connection. The fracture location is verified by the finite element analysis (FEA). Then, the loosening torque of the screw under static and dynamic loads was measured. Finally, the surface fracture morphology of the implant system and surface wear morphology of the screw were observed. The results show that the PNT could reduce the friction coefficient and increase the preload force. Plasma nitriding significantly affected the fatigue property. The PNT increased the fracture load and elongated the fatigue life. In addition, the PNT improved the anti-loosening performance under dynamic load. Most of the fatigue fracture occurred at the neck region of the implants and the first thread of the abutment screws, consistent with the FEA results. Plasma nitriding can reduce the wear of screw surfaces and protect the integrity of the thread. Therefore, the PNT effectively improves the long-term stability of the implant system.
Ti-6Al-4V alloy has wide applications in the medical industry due to its unique mechanical properties and biocompatibility. However, in the long-term use of these alloys, the release of aluminum and vanadium can result in serious illnesses. For solving these problems, the implant surface modification can be done to improve the corrosion and biocompatibility properties. In this study, TiN coating was applied by Plasma-Assisted Chemical Vapour Deposition (PACVD) method along with hydroxyapatite coating (HA) by sol-gel method on Ti-6Al-4V substrate surface. Afterwards, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM) and potentiodynamic polarization and electrochemical impedance tests were used for evaluating the phase, morphology, chemical composition, surface roughness, and corrosion behavior in the simulated body fluid (SBF), respectively. Results showed that the surface roughness of HA/TiN, HA, TiN and substrate specimens were the highest to minimum values with roughness of 30.86 ± 0.5, 25.1 ± 0.42, 20.43 ± 0.14 and 15.1 ± 0.02 nm, respectively, and the HA-TiN composite coating had the lowest corrosion current density, highest polarization resistance and corrosion potential. Results of cell viability and proliferation demonstrated that the HA/TiN nanocomposite coating is a good choice for dental and orthopedic implants due to its corrosion resistance and biocompatibility.
In this study, Ni-Mo alloy films with different weight ratios were coated on mild steel (G10700) by a novel and effective co-sputtering method, and their corrosion protection was investigated in 3.5 % NaCl solution. In the sputtering process, Ni and Mo targets were mounted at DC and RF sputtering guns, respectively. By introducing the sputtering gas (argon), bimetallic films were prepared under changing the power at the RF gun and keeping the current constant at the DC gun of the magnetron sputtering system. The coatings were characterized by different methods and their corrosion resistance in 3.5 % NaCl solution was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The results of corrosion testing revealed that there is a relation between roughness and corrosion resistance, and all of the coatings (mono and bimetallic) have a protective effect, however, the highest performance was obtained at bimetallic coatings which the best composition was for the Mo-to-Ni weight ratio of 4.5 and 0.15 for 2 min and 1-week exposure time to the corrosive solution, respectively.
TiO 2 -Ag composite films are deposited on glass substrates by a novel grid-assisted co-sputtering method, aiming at preparing films with different silver contents. The films are characterized by energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, atomic force microscopy (AFM), ultraviolet-visible spectroscopy, and photoluminescence spectroscopy. Furthermore, the parameters of saturation roughness, fractal spectra, and permutation entropy are utilized to analyze the AFM images; the permutation entropy is employed in a 2D matrix to measure the complexity. The atomic ratios of silver to titanium range from 0.09 to 7.80, and the observed optical band gaps are in the range of 3.17 to 3.26 eV. Photoluminescence spectroscopy reveals the photoinduced-electron-trapping effect of Ag particles in the structure and surface of the films governs the emission intensities. The AFM images show the roughness of the films increases by increasing the Ag content, and it can be seen that an increase in the TiO 2 content of the films results in an increase in fluctuation per area, hence increasing the permutation entropy. Therefore, it is proposed that the Ag content of the films could be predicted by surface roughness and permutation entropy measurements; the fractality of the data allows a more precise determination of silver content.
In this research, Ti-Cr-N coatings on tool steel were prepared using DC magnetron sputtering at 25 °C (RT), 130 °C and 190 °C. Coating corrosion behavior was observed in a 3.5% NaCl solution at 25 °C using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS). EIS circuit models for corrosion kinetics were proposed and the surface area and porosity of the coatings were recorded. Corrosion resistance was found to be higher for the coatings grown at 190 °C. This could be attributed to high density as well as low porosity. The EIS circuit model suggests the penetration of corrosive electrolytes into pores reaching the steel substrate for the coatings grown at RT. Finite length diffusion inside pores was also observed. The slow infiltration of corrosive electrolytes into the steel substrate could be seen in coatings grown at 130 °C with diffusion inside the pore similar to that in the coatings grown at RT. However, the EIS circuit model did not exhibit a finite length diffusion of the coatings grown at 190 °C. Owing to high coating density and smaller pore size, corrosive electrolytes could hardly penetrate through and reach the steel substrate.
In this study, submicron nanocrystalline TiCrN films (141 nm, ± 8 nm) are deposited on titanium-coated steel substrates, maintained at a temperature of 300 °C. The bilayer films are prepared via an RF-DC co-sputtering system under different nitrogen flow rates (7, 10, 15, and 18 sccm). The compositional, nanostructural, mechanical, and morphological properties of the bilayer films are characterized by energy-dispersive X-ray spectroscopy (EDS), grazing incidence X-ray spectroscopy (GIXRD), backscattered scanning electron microscopy (BSE), nanoindentation and nanoscratch tests, and atomic force microscopy (AFM). The EDS results reveal that the chemical composition of the top layers is Ti1Cr1+XN with −0.06 < X < 0.21. The GIXRD patterns show that a face-centered cubic solid solution structure with a relatively strong (111) texture has been formed on a hexagonal close-packed structure (α-Ti). In addition, it can be seen the crystallite size has slightly increased in the samples with higher nitrogen content while the interplanar spacing has decreased in the samples with higher chromium content. The nanoindentation and nonoscratch tests are performed under three different indentation loads (300, 500, and 1000 µN), and the residual impressions are studied by AFM images. The results of the nanoindentation tests demonstrate that the sample with the smallest interplanar spacing, the largest crystallite size and the highest nitrogen content exhibits the highest Cube Corner hardness value. The results of the nanoscratch tests suggest that the impact of surface roughness on the friction coefficient is less dominant as the ratio of root-mean-square roughness to penetration depth decreases and that the chromium content is the factor that means the friction coefficient differences. Comparing the hardness and the friction coefficient of the samples at the load of 1000 μN, it can be said that the hardness value has improved by 25% while the friction coefficient has lowered by 14%, with the lowest value of 0.3.
A comprehensive over view of the process named as 'digestive ripening' that is known to convert polydisperse nanocrystals to monodisperse ones is presented. Apart from highlighting the role of organic molecules (ligands) in achieving size control the role of other parameters like the nanocrystal-ligand binding strength and the temperature at which the reaction is carried out in accomplishing size control is also delineated. The generality of the procedure is illustrated by providing examples of how it is used to prepare monodispersed nanocrystals of different metals, alloy systems, ultra small nanocrystals and also to narrow the size distribution in complex binary and ternary nanocrystal systems. Finally, the current status as far as the theoretical understanding of how the size control is being achieved by digestive ripening is laid out, emphasizing at the same time the necessity to undertake more systematic studies to completely realize the full potential of this practically very useful procedure.
Chromium nitride coatings are synthesized on the stainless steels by plasma immersion ion implantation and deposition. The microstructure and tribocorrosion behaviors of the as-deposited coatings are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, reciprocating-sliding tribometer and electrochemical testing. The results show that the CrN coatings have a typical columnar growth structure consisting of face-centered cubic crystals. The CrN coatings greatly enhance the corrosion resistance and wear resistance of the stainless steel. However, frictional forces induce numerous micro-cracks which act as the diffusion channels for NaCl solution. Multi-scale Cl ion corrosion occurs simultaneously during the tribocorrosion and a force-corrosion synergy interaction induces the multi-degradation (e.g., intersecting cracks and layer delamination) of the CrN coating. The synergistic damage mechanisms of wear and corrosion are systematically discussed.
Statement of problem:
The passive film on the surface of titanium can be destroyed by immersion in a fluoridated acidic medium. Coating with titanium nitride (TiN) may improve the corrosion resistance of titanium.
Purpose:
The purpose of this in vitro study was to investigate the effect of duplex treatment with plasma nitriding and TiN coating on the corrosion resistance of cast titanium.
Material and methods:
Cast titanium was treated with plasma nitriding and TiN coating. The corrosion resistance of the duplex-treated titanium in fluoride-containing artificial saliva was then investigated through electrochemical and immersion tests. The corroded surface was characterized by scanning electron microscopy (SEM) with energy-dispersive spectroscopy surface scan analysis. The data were analyzed using ANOVA (α=.05) RESULTS: Duplex treatment generated a dense and uniform TiN film with a thickness of 4.5 μm. Compared with untreated titanium, the duplex-treated titanium displayed higher corrosion potential (Ecorr) values (P<.001) and lower corrosion current density (Icorr) values (P<.001). SEM results showed that the surface of untreated titanium was more heavily corroded than that of duplex-treated titanium. Surface scan analysis of duplex-treated titanium that had been immersed in artificial saliva containing 2 g/L fluoride revealed fluorine on the titanium surface, whereas fluorine was not observed on the surface of untreated titanium after immersion in fluoride-containing artificial saliva. The concentration of titanium ions released from the treated titanium was less than the amount released from untreated titanium (P<.001).
Conclusions:
Duplex treatment by plasma nitriding and TiN coating significantly improved the corrosion resistance of cast titanium in a fluoride-containing environment.
This chapter discusses nanocrystalline (<100. nm) and ultrafine-grained metals and alloys with an emphasis on those relevant to the biomedical community. Biomedical metals and alloys that have been produced in nanocrystalline or ultrafine-grained form to date and their processing routes are first discussed. Grain size-dependent properties, including mechanical, tribological and corrosion properties, as well as the cellular response to nanocrystalline and ultrafine-grained materials are reviewed. Finally, existing and future medical applications of nanocrystalline and ultrafine-grained metals and alloys are discussed.
Nickel is a metal of widespread distribution in the environment: there are almost 100 minerals of which it is an essential constituent and which have many industrial and commercial uses. Nickel and nickel compounds belong to the classic noxious agents encountered in industry but are also known to affect non-occupationally exposed individuals. The general population may be exposed to nickel in the air, water and food. Inhalation is an important route of occupational exposure to nickel in relation to health risks. Most nickel in the human body originates from drinking water and food; however, the gastrointestinal route is of lesser importance, due to its limited intestinal absorption. The toxicity and carcinogenicity of some nickel compounds (in the nasal cavity, larynx and lungs) in experimental animals, as well as in the occupationally exposed population, are well documented. The objective of this paper is to summarize the current overview of the occurrence and sources of nickel in the environment, and the effect of this metal and its compounds on living organisms. As this topic is very broad, this review is briefly concerned with the toxicokinetics of nickel, its health effects and biological monitoring.
Concretes can be defined as artificial stones produced when cement, usually Portland cement, is mixed with a fine aggregate (such as sand); a coarse aggregate (gravel or crushed stones), and water. The intended application of concrete dictates the proportioning of major concrete ingredients and cement types, as well as particle-size gradations of the fine coarse aggregates. Definitions and a brief explanation of important terms related to concrete are given to familiarize engineers with the applications of concrete. The effect of properties and characteristics of aggregates that affect the characteristics of concrete are analyzed in the chapter. The use of suitable mixing water is essential to make good concrete, and any unmineralized water can be used for this. The chapter discusses the engineering properties of concrete. The chemistry of concrete primarily involves a study of hydration products of concrete formed on addition of water. The most commonly used coatings include acrylic, chlorinated rubber, and polyurethane coating. Mapping is used widely to identify the areas of corrosion risk on reinforcing steel. In addition to the major techniques used for evaluation of corrosion of the reinforcing steel described, nondestructive techniques—such as computed tomography, impact echo and magnetic field disturbance, electrochemical noise, and other techniques—have also been used for the inspection and detection of corrosion of reinforcing steels.
This chapter discusses the kinetics of corrosion. The classical electrochemical work conducted by Michael Faraday in the 19th century produced two laws that were published in 1833 and 1834 and were named after him. The chapter discusses the two laws and their applications. Thermodynamics gives an indication of the tendency of electrode reactions to occur, whereas electrode kinetics addresses the rates of such reactions. The reactions of concern are mainly corrosion reactions, and hence, it is more appropriate to call the kinetics of such reactions as corrosion kinetics. Chloride ions damage protective films and cause metal surfaces to be pitted. Stainless steel is subjected to serious pitting by stagnant water containing high concentration of chloride ions. An increase in temperature generally decreases passive range and increases critical current density. An increase of temperature decreases polarization and enhances dissolution kinetics. At a particular velocity (critical velocity), the rate becomes activation controlled rather than diffusion controlled, and hence, the rate of corrosion becomes independent of velocity.
The purpose of this investigation was to develop titanium nitride (TiN)/titanium (Ti) coating on orthodontic nickel–titanium (NiTi) wires and to study the stress corrosion of specimens in vitro, simulating the intra-oral environment in as realistic a manner as possible. TiN/Ti coatings were formed on orthodontic NiTi wires by physical vapor deposition (PVD). The characteristics of untreated and TiN/Ti-coated NiTi wires were evaluated by measurement of corrosion potential (Ecorr), corrosion current densities (Icorr), breakdown potential (Eb), and surface morphology in artificial saliva with different pH and three-point bending conditions. From the potentiodynamic polarization and SEM results, the untreated NiTi wires showed localized corrosion compared with the uniform corrosion observed in the TiN/Ti-coated specimen under both unstressed and stressed conditions. The bending stress influenced the corrosion current density and breakdown potential of untreated specimens at both pH 2 and pH 5.3. Although the bending stress influenced the corrosion current of the TiN/Ti-coated specimens, stable and passive corrosion behavior of the stressed specimen was observed even at 2.0 V (Ag/AgCl). It should be noted that the surface properties of the NiTi alloy could determine clinical performance. For orthodontic application, the mechanical damage destroys the protective oxide film of NiTi; however, the self-repairing capacity of the passive film of NiTi alloys is inferior to Ti in chloride-containing solutions. In this study, the TiN coating was found able to provide protection against mechanical damage, while the Ti interlayer improved the corrosion properties in an aggressive environment.
Analysis of experimental EIS data in terms of equivalent circuits is the common approach used in most commercial software dedicated to EIS method. However, one-to-one assignment of impedance elements to particular electrochemical/physical processes causes difficulty, at the exception of the impedance calculated for one-step reactions. The example of EE reaction is dealt with in this article for the purpose of illustrating non-intuitive and sometimes unexpected features of equivalent circuits derived for a two-step electrochemical reaction involving only soluble diffusing species and electrons.
Binary (Ti/TiN and Cr/CrN) and ternary (TiCr/TiCrN) thin films were deposited on AL7075-T6 by magnetron sputtering. Microhardness, adhesion strength and pin-on-plate wear tests were performed to investigate coating performance. Field emission scanning electron microscope integrated with focused ion beam milling and energy dispersive X-ray spectroscopy was employed for microstructural and chemical characterizations. The tribo-mechanical test results revealed that Cr/CrN promoted up to 5 times greater hardness, Ti/TiN showed the highest scratch resistance and up to 8 times reduced wear, while TiCr/TiCrN favored the least friction and surface roughness. Furthermore, the excellent tribological properties of coatings correlated with their superior adhesion to AL7075-T6.
Highly porous Ti-Cu alloy foams were produced by powder metallurgy method for implant applications. Ti-Cu alloys were prepared with 3, 5, 7, and 10 wt pct Cu contents in order to determine optimum Cu addition. Cu addition enhances sinterability, and the Ti-Cu compacts were sintered at lower temperatures and times than pure Ti. Specimens were coated with a TiN film to enhance wear and corrosion resistance. Sintered specimens were precipitation hardened (aged) in order to increase mechanical properties. Corrosion properties of foams were examined by electrochemical techniques, such as potentiodynamic polarization, cyclic polarization, Tafel extrapolation, linear polarization resistance, and open-circuit potential measurement. Effect of Cu content, TiN coating, pH, and fluoride content of artificial saliva on electrochemical corrosion behavior of specimens was investigated.
This study examined the effects of TiN (titanium nitride) and WC (tungsten carbide) coatings on the fatigue characteristics of dental implants using a sinusoidal cyclic loading machine under load between 42-420 N and 58-580 N according to the ISO 14801. In this study, an abutment screw was coated with a TiN and WC film by EB-PVD and sputtering, respectively. For the fatigue test, the implant fixture and abutment were tightened to a torque 32 Ncm using a digital torque gauge with 0.1 Ncm accuracy. Field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) were used to observe the coated surface and fracture surface of the abutment screw. The uncoated abutment screws contained scratches caused by the mechanical process, whereas the TiN and WC coated screws showed a smooth surface at the screw thread and screw valley. The mean fatigue life of the uncoated, TiN coated, and WC coated abutment screw at 420 N was 5.8 x 10(5), 8.2 x 10(5) and 10(6) cycles, respectively. At 580 N, the mean fatigue life of the uncoated, TiN coated and WC coated abutment screw was 2.1 x 10(4), 4.1 x 10(4) and 2.3 x 10(4) cycles, respectively. The uncoated abutment screw showed the beach mark and fatigue striation. On the other hand, in the case of TiN and WC coated abutment screws, the semi-cleavage fracture and ductile fracture appeared at 420 N. Semi-cleavage fracture and massive fatigue striation with a step of 0.5 mu m/cycle were observed in TiN coated abutment screw, whereas a minute slip band was noted and the interval of fatigue striation increased to several mu m/cycle in the WC coated screw at 580 N.
The study of galvanic coupling between two metals is still a relevant topic, particularly in aerospace and automotive industries. The development of local electrochemical techniques leads to a better understanding of the phenomena occurring at the interfacial zone. Galvanic coupling between carbon steel and zinc was investigated by local electrochemical impedance spectroscopy (LEIS) in a 0.06 g L−1 NaCl solution. Voltammetry and conventional electrochemical impedance experiments were also performed to better analyze the local impedance data. Local measurements carried out at a fixed frequency showed that zinc dissolution was more significant at the steel/zinc interface. A particular shape of the local impedance diagram was observed above the zinc surface with the presence of a large inductive loop in the low-frequency range. Numerical simulations, performed by using finite element method, allowed the local experimental diagrams obtained over the zinc sample to be validated taking into account the radial contribution of the current between both materials in galvanic coupling.
The oxidation behavior of TiCrN coatings having compositions of Ti36Cr26N38, Ti31Cr35N34 and Ti14Cr52N34 was studied between 700 and 1000°C in atmospheric air. The oxidation resistance of TiCrN coatings which were composed of TiN and CrN phases increased in the order of Ti36Cr26N38, Ti31Cr35N34 and Ti14Cr52N34, implying that chromium within the coating played a decisive role in providing the oxidation protection. The oxides formed always consisted of TiO2 and Cr2O3. During oxidation, all the involved elements diffused either outwardly or inwardly, depending on the concentration gradients. The substrate elements diffused outwardly toward the oxide-gas interface, oxygen from the atmosphere diffused inwardly and the coating elements diffused predominantly outward.
In this paper, four kinds of hard coatings, TiN, CrN, TiAlN and CrAlN (with Al/Ti or Al/Cr atomic ratio around 1:1), were deposited on stainless steel substrates by a lateral rotating cathode arc technique. The as-deposited coatings were annealed in ambient atmosphere at different temperatures (500–1000 °C) for 1 h. The evolution of chemical composition, microstructure, and microhardness of these coatings after annealing at different temperatures was systematically analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and nanoindentation experiments. The oxidation behaviour and its influence on overall hardness of these four coatings were compared. It was found that the ternary TiAlN and CrAlN coatings have better oxidation resistance than their binary counterparts, TiN and CrN coatings. The Cr-based coatings (CrN and CrAlN) exhibited evidently better oxidation resistance than the Ti-based coatings (TiN and TiAlN). TiN coating started to oxidize at 500 °C. After annealing at 700 °C no N could be detected by EDX, indicating that the coating was almost fully oxidized. After annealed at 800 °C, the coating completely delaminated from the substrate. TiAlN started to oxidize at 600 °C. It was nearly fully oxidized (with little residual nitrogen detected in the coating by EDX) and partially delaminated at 1000 °C. Both CrN and CrAlN started to oxidize at 700 °C. CrN was almost fully oxidized (with little residual nitrogen detected in the coating by EDX) and partially delaminated at 900 °C. The oxidation rate of the CrAlN coating is quite slow. After annealing at 1000 °C, only about 19 at.% oxygen was detected and the coating showed no delamination. The Ti-based (TiN and TiAlN) coatings were not able to retain their hardness at higher temperatures (≥ 700 °C). On the other hand, the hardness of CrAlN was stable at a high level between 33 and 35 GPa up to an annealing temperature of 800 °C and still kept at a comparative high value of 18.7 GPa even after annealed at 1000 °C, indicating a very promising applicability of this coating for high speed dry machining and other applications under high temperature environments.
The effects of multilayered Ti/TiN or single-layered TiN films deposited by pulse-biased arc ion plating (PBAIP) on the corrosion behavior of NiTi orthodontic brackets in artificial saliva are investigated. The multilayered Ti/TiN coating is found to exhibit a greater free corrosion potential, much lower passive current density, and no breakdown up to 1.5 V. Moreover, electrochemical impedance spectroscopy (EIS) results indicate that the multilayered Ti/TiN coating has a larger impedance and lower porosity which is believed to be responsible for the exceedingly low metal ion release rate during 720 h exposure in the test solution. Visual inspection of the surfaces reveals different corrosion processes for the TiN and multilayered Ti/TiN coatings.
The corrosion behaviour of TiN, (TiAl)N and CrN coated on 304 stainless steel by physical vapour deposition was examined in borate solution (pH 9.0) and in 0.5 M NaCl solution. The study was performed by using open circuit potential, potentiodynamic polarization and cyclic polarization techniques, complemented with XRD and laser microscopy. The measurements were also performed on the uncoated substrate for comparison. Nitrided coatings significantly improve the corrosion performance of the steel; however, they are prone to corrosive attack as a consequence of the presence of microstructure defects such as pinholes and pores. Galvanic corrosion between the coatings and the substrate result in significant attack of the substrate, allowed by the penetration of small pinholes into the substrate. In borate solution, (TiAl)N possesses the highest corrosion resistance. However, CrN possessed the highest corrosion resistance in NaCl solution.
In this work, we report on the determination of surface diffusion coefficient of copper on tantalum substrates by Ostwald ripening. It is shown that impurities, such as oxygen, strongly influence the kinetics of dewetting of copper films on tantalum substrates. Two technologically important interfaces with copper were investigated: Cu/β-Ta and Cu/α-Ta. For copper surface diffusion on β-Ta surface, a surface diffusion coefficient of was measured at 550 °C. The temperature dependence of surface diffusion was investigated between 400 °C and 550 °C. Using an Arrhenius relationship, an activation energy of 0.83 ± 0.1 eV and a pre-exponential factor of were calculated. For copper surface diffusion on α-Ta surface, a diffusion coefficient of was measured at 550 °C. We discuss the diffusion mechanism involved during the cluster growth and the origin of the faster surface diffusion of copper on the β-Ta substrate as compared to the α-Ta phase.