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Effects of Electroplated Zinc-Nickel Alloy Coatings on the Fatigue Strength of AISI 4340 High-Strength Steel

  • Univ. Estadual Paulista - UNESP

Abstract and Figures

Recovered substrates have been extensively used in the aerospace field. Cadmium electroplating has been widely applied to promote protective coatings in aeronautical components, resulting in excellent corrosion protection combined with a good performance in cyclic loading. Ecological considerations allied to the increasing demands for corrosion resistance have resulted in the search for possible alternatives. Zinc-nickel (Zn-Ni) alloys have received considerable interest recently, because these coatings show advantages such as a good resistance to white and red rust, high plating rates, and acceptance in the market. In this study, the effect of electroplated Zn-Ni coatings on AISI 4340 high-strength steel was analyzed for rotating bending fatigue strength, corrosion, and adhesion resistance. The compressive residual stress field was measured by x-ray diffraction prior to fatigue tests. Optical microscopy documented coating thickness, adhesion characteristics, and coverage extent for nearly all substrates. Fractured fatigue specimens were investigated using scanning electron microscopy (SEM). Three different Zn-Ni coating thicknesses were tested, and comparisons with the rotating bending fatigue data from electroplated Cd specimens were performed. Experimental results differentiated the effects of the various coatings on the AISI 4340 steel behavior when submitted to fatigue testing and the influence of coating thickness on the fatigue strength.
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H. J. C. Voorwald , I.M. Miguel and M.Y.P. Costa
Department of Materials and Technology, State University of São Paulo, Cep. 12516-410, BRAZIL.
It is well known that fatigue behaviour is an important parameter to be considered in mechanical components
subjected to constant and variable amplitude loadings. In combination with corrosion phenomenon, fatigue
effects were responsible for proximally 64% of fails that occur in metallic parts of aeronautical accidents in
the last 30 years. Recovered substrates have been extensively used in the aerospace field. Cadmium
electroplating has been widely applied to promote protective coatings in aeronautical components, resulting
in excellent corrosion protection combined with a good performance in cyclic loading. Ecological
considerations allied to the increasing demands for corrosion resistance, resulted in the search for possible
alternatives. Zinc-nickel alloys received considerable interest recently, since these coatings showed some
advantages such as a good resistance to white and red rust, high plating rates and acceptation in the market. In
this study the effects of zinc-nickel coatings electroplated on AISI 4340 high strength steel were analysed on
rotating bending and axial fatigue strength, corrosion and adhesion resistance. Compressive residual stress
field was measured by a X-ray tensometry prior to fatigue tests. Optical microscopy images showed coating
thicknesses, adhesion and the existence of an uniform coverage of nearly all substrates. The fractured fatigue
specimens were investigated using a scanning electron microscope. Three different zinc-nickel coating
thicknesses were tested and comparison with rotating bending fatigue data from specimens cadmium
electroplated and heat treated at 190°C for 3, 8 and 24 hours to avoid the diffusion of hydrogen in the
substrate, was performed. Experimental results showed effect of coatings on the AISI 4340 steel behaviour
when submitted to fatigue testing and the existence of coating thickness influence on the fatigue strength.
In recent years, with higher worldwide demand for improved quality and corrosion resistance,
alternative coatings are required. Zinc alloys, particularly zinc-nickel, have been extensively
studied due to their technological application in protection against corrosion, as an alternative to
cadmium alloys [1-3]. These coatings are widely applied in automotive industry, normally with
thicknesses of 10 µm [4]. These alloys have also been considered for several applications such as
in electrocatalytic water electrolysis [5], as coatings for steel cord reinforcement of tires [6] and in
the electronics industry [7]. In the Brazilian aeronautical industry, despite of the excellent
properties as agent protective showed by Zn-Ni coatings, these alloys are still in study and in a
development stage. In this industrial segment, a good resistance to fatigue is required, which
result in another difficulty in the search of alternatives to cadmium as coatings in high strength
In case of aeronautical applications, protection against corrosion must be combined with fatigue
The aim of this study was to analyze the effects on AISI 4340 steel, in the rotating bending
fatigue behavior, of zinc-nickel coating thickness electroplated on AISI 4340 steel and to compare
with the results obtained by cadmium electroplating. Fracture planes of the fatigue specimens were
examined using a scanning electron microscopy in order to identify the crack initiation points.
Optical metallographic was used to investigate the existence of an uniform coverage of nearly all
Studies of the resistance against corrosion were carried out using salt spray tests and the results
showed according to ASTM B117. The residual stresses promoted by machining and the
electroplating process were obtained and compared with base material.
Residual stresses were determined by X-ray diffraction method, using the Ray stress
equipment, whose characteristics are described in [8]. The accuracy of stress measurements was
∆σ = ±20 MPa. In order to obtain the stress distribution by depth, the layers of specimens were
removed by electrolytic polishing with a non-acid solution.
The base material used in this work was the AISI 4340 steel widely applied in aircraft components
where strength and toughness are fundamental design requirements. The chemical composition of
the steel is in accordance to required standards.
Rotating bending fatigue test specimens were machined from hot rolled quenched and tempered
bars. Fatigue tests specimens were quenched from (815 – 845) °C in oil (20 °C) and tempered in
the range (520 ± 5) °C for two hours. Mechanical properties of the steel after the treatment are:
hardness = (38 – 42) HRc, yield strength = 1118 MPa and ultimate tensile strength = 1210 MPa.
After final preparation, specimens were subjected to stress relieve heat treatment at 190 °C for four
hours with posterior cooling in still air, to reduce residual stresses induced by machining.
Specimens were machined according to specifications, polished with 600 grit papers, inspected
dimensionally and by magnetic particle inspection. Average superficial roughness in the reduced
section of the specimens was Ra 2.75 µm with standard deviation equal to 0,89 µm.
The cadmium electroplating was carried out by rotative drum process, during 1 minute to 10
minutes to produce coating thicknesses in the range 8 µm to 13 µm. Parameters employed in this
process were: cadmium salt solution 20 – 30 [g/l], sodium cyanide solution 90 - 200 [g/L], sodium
hydroxide solution 10 – 20 [g/L], relations Cn/Cd equal 4:1 – 6:1, temperature room, continuous
current between 1 – 5 [A/dm2], voltage anode/cathode 1 – 4 [volts] and electrodeposition velocity
between 0,2 – 1,5 [µm/min]. Once finished the bath deposition, specimens were treated with
sodium cyanide solution for 15 seconds to 30 seconds, treated with stream water and dried with
hot air for 2 minutes to 4 minutes. The last step in the cadmium electrodeposition process was
dehydrogenation by heat treatment to avoid the diffusion of hydrogen in the substrate.
The zinc-nickel electroplating was carried out in accordance to the plating control parameters
shown in table 1. Prior to the deposition, pieces were submitted to the following sequence of
pretreatment: alkaline clean, acid pickling and rinsing with distilled water. After plating,
specimens were subjected to rinsing and drying and submitted to hydrogen embrittlement relief
treatment at 190 ºC for 24 hours.
Rotating bending fatigue tests were performed using a sinusoidal loading at frequency of 50 Hz
with stress ratio R equal to –1,0 in air and at room temperature. These tests consider as fatigue
strength complete fracture of the specimens or 107 load cycles. Nine groups of fatigue specimens
were prepared to obtain S-N curves for rotating bending fatigue tests.
The residual stress analysis were conduced by portable X-ray apparatus with an air cooled double-
anode X-ray tube, provided with a stress measurement unit and focusing camera for phase
analysis. The characteristics of the equipment used in this analysis were showed by Monin et al
[9] and the methodology applied during the tests is described. Specimens used in these tests have
the same specification adopted in the fatigue tests. Measurements were carried out with base
material and base material zinc-nickel alloy electroplated, at the interface substrate/coatings and
inside substrate.
Fracture surface analysis was carried out on rotating bending fatigue test specimens by scanning
electron microscope, model Leo 435 Vpi. The metallographic analysis was carried out by optical
microscope model Neophot 21.
Images were used to identify the existence or not of an uniform coverage of nearly all
substrates and to investigate the better performance of the coatings with respect to their adherence
properties. Thicknesses of the coatings were measured and compared in order to verify their
relationship with fatigue behavior. The metallographic analysis was carried out on specimens
sectioned in the transversal orientation, inlaid work in acrylic resin, prepared using 80 at 1000
graduate waterproof papers and polished with 99,98% Alumina suspension.
Figure 1 shows SxN curves for rotating bending fatigue tests for the base material, hard chromium
electroplating, cadmium electroplating and zinc-nickel electroplating.
BASE MAT. & ZI NC-NICKEL (7µm-12µm).
BASE MAT. & ZI NC-NICKEL (15µm-21µm).
BASE MAT. & ZI NC-NICKEL (2µm-6µm).
BASE MAT. & CHROM IUM (160µm).
Figure 1: Rotating Bending fatigue test. Based material, zinck-nickel alloys, cadmium and
chromium electroplated specimen.
Experimental data for base material in figure 1 will be used in this work as a reference to be
compared with the fatigue strength of AISI 4340 steel electroplated with cadmium and zinc-nickel
alloys. It is possible to observe from figure 1 the significant reduction in the fatigue life of
specimens chromium electroplated.
The SxN curve for the specimens tested after cadmium electroplating, without post heat
treatment shows decrease in fatigue strength in comparison to the base material, for low and high
To understand the effect of zinc-nickel electroplated coating on the SxN curves of AISI 4340
steel, figure 2 should be considered. From figure 2, which indicates residual stress at interface
substrate-coating and inside base metal it is possible to observe that compressive residual stresses
at interface decreases with the decrease in the coating thickness. Maximum compressive residual
stress at interface is obtained for base metal. Interesting is to observe the variation of residual
stress increasing the distance from the interface. After 0.1 mm, specimens zinc-nickel electroplated
coated with thicknesses in the range of 7 µm - 12 µm and 15 µm - 21 µm, showed tensile residual
stresses of 20 MPa and 60 MPa, respectively. For base material and zinc-nickel electroplated
coating in the range of 2 µm - 6 µm, table 1 shows that at 0.1 mm from the interface residual
stresses are – 260 MPa and 20 MPa, respectively.
0,0 0,1 0,2
2 µm - 6 µm - 39 HRc
7 µm - 12 µm - 39 HRc
15 µm - 21 µm - 39 HRc
Figure 2: Residual stress measurements tests.
At 0.2 mm from the interface, all conditions show tensile residual stresses, in the range 20 MPa
to 100 MPa. It is interesting to observe for zinc-nickel electroplated coating 15 µm – 21 µm, the
variation in the residual stresses from 500 MPa compressive at interface to 60 MPa tensile at 0.1
mm from this point. Comparison between residual stresses at 0.1 mm and 0.2 mm from the
interface indicate, exception made for the base metal, almost the same results, for zinc-nickel
electroplated coatings.
It is well known that delay in fatigue crack nucleation and propagation results from the
presence of compressive residual stress field which, consequently, increase fatigue strength.
Compressive residual stress at interface for thicknesses 2 µm - 6 µm, 7 µm - 12µm and 15 µm – 21
µm were 90 MPa, 210 MPa and 500 MPa, respectively. To understand the behavior of the SxN
curves represented in figure 3, residual stresses at 0.1 mm from the interface coating-substrate
must be considered. The highest residual stresses was obtained for zinc-nickel electroplated
coating with thickness 15 µm – 21 µm, in comparison to 2 µm - 6 µm and 7 µm – 12 µm.
Figure 2 indicates residual stresses behavior with compressive values at interface and tensile at
0,1 mm from that point, for base material and the three zinc-nickel electroplated coating
thicknesses studied.
Figure 3: Optical microscopy. Thicknesses and homogeneity of zinc-nickel layers: (a) = 2 µm –
6 µm, (b) = 7 µm - 12 µm and (c) = 15 µm - 21 µm.
Figure 4: Scanning electronic microscopy. AISI 4340 zinc-nickel alloy coatings. Thicknesses
between 15 µm - 21 µm.
Figure 3 (a) shows an optical microscopy image of zinc-nickel electroplated coating, 2µm – 6
µm thick, with 1000 X magnification. It is possible to verify that the coating layer is uniform and
there are no signs of detachment of coating from the substrate. Figures 3 (b) and 3 (c) represent
images from coating thicknesses 7 µm – 12 µm and 15 µm – 21 µm. Coating homogeneity and
strong adhesion with substrate are observed.
Figures 4 (a), (b) and (c) show represent fracture surfaces a rotating bending fatigue specimen
tested at 951 MPa, fractured after 10600 cycles. Electroplated zinc-nickel coating thickness was in
the range 15 µm – 21 µm. Figure 4 (a) represent the general fracture surface aspect with several
crack origin sites around specimen surface. Figure 4 (b), indicates fatigue crack nucleation at
interface coating-substrate. In figure 4 (c), fatigue crack nucleation at interface and propagation
inside substrate, is shown. Figures 4 (d), (e) and (f) are associated to a fatigue specimen tested at
571 MPa, with a number of cycles to fracture equal to N = 83600.
Figures 4 (e) and (f) indicate fatigue crack nucleation inside substrate, associated to the
variation in residual stresses from 500 MPa compressive at interface to 600 MPa tensile at 0.1 mm
from this region.
1. For low cycle fatigue, differences in fatigue strength specimens exposed to 190 °C for 2, 8
and24 hours were not observed. In high cycle fatigue some influence was detected, indicating
better results for lower treatment times.
2. Reduction in the AISI 4340 steel rotating bending fatigue strength resulted from zinc-nickel
electroplated coating in the thickness interval 15 µm - 21 µm. In the case 7 µm - 12 µm,
experimental data indicate almost the same behavior, with respect to the fatigue strength,
showed by AISI 4340 steel cadmium electroplated, 8 µm - 13 µm.
I. M. Miguel, C. E. A. Silva, M. P. Peres, H. J. C. Voorwald. Study of influence of zinc-nickel
and cadmium electroplated coatings on fatigue strength of aeronautical steels. FATIGUE, 2002, p.
S. B. Silva, L. H. Mascaro, S. A. S. Machado and L. A. Avaca Análise da composição de ligas
de Zn-Ni depositadas sobre diferentes materiais. EBRATS 94. (1994) p. 15-23.
G. F. Hsu, Zinc-nickel alloy plating: An alternative to cadmium. Plating and Surface Finishing.
71,4 (1984) p. 52-55.
A. M. Alfantazi and U. Erb. Corrosion properties of pulse-plated zinc-nickel alloy coatings.
Corrosion Engineering. (1996) pp. 880-888.
M. J. Giz; S. A. Machado, L. A. Avaca and E. R. Gonzalez. High area Ni-Zn and Ni-Co
codeposits as hydrogen electrodes in alkaline solutions. Journal of Applied Electrochemistry, 22
(1992) p. 973-977.
J. Giridhar, W. J. Ooij, Surface Coating and Technology. 53 (1992) 35.
R. G. Baker and C. A. Holden. Zinc-nickel alloy electrodeposits: Rack plating. Plating and
Surface Finishing, 72, 3 (1985) p. 54-57.
T. Gurova. Study of the residual stress state during plastic deformation under uniaxial tension in
a 5,0 Cr and 0,5 Mo steel. Science Material. 36(9) (1997) p. 1031-1035.
V. Monin, J. R. Teodosio, and T.Gurova. A Portable X-ray apparatus for both stress
measurement and phase analysis under field conditions. Advances in X-ray Analysis. 43 (2000)
p. 66-71.
The authors are grateful for the support of this research by CAPES, ELEB/EMBRAER and
... An electroplated chromium coating significantly affects fatigue behavior due to tensile residual stresses and microcracks [7]. Cadmium electrodeposition may reduce the fatigue strength due to hydrogen embrittlement [8]. Therefore, the fatigue lifetime of Cd-coated components could decrease compared to the base metal, due to cracks at the coated surface and due to the hydrogen embrittlement induced by the electrodeposition process. ...
... The fatigue life increased for both Cd and Zn-Ni conditions. The explanation for this behavior is the residual stress field generated near the surface due to the electrodeposition process and the effect of dehydrogenation heat treatment on the residual stress field [8,17]. The difference between the fatigue life of the two coated conditions could be explained by the difference in residual stress levels and coating thicknesses. ...
Full-text available
The influence of the electrodeposition of cadmium and zinc-nickel and the stress concentration effect on the fatigue behavior of AISI 4140 steel threaded components were studied. Axial fatigue tests at room temperature with a stress ratio of R = 0.1 were performed using standard and threaded specimens with and without nut interface under base material, cadmium, and zinc-nickel-coated conditions. Finite element analysis (FEA) was used, considering both elastic and elastoplastic models, to quantify the stress distribution and strain for threaded specimens with and without a nut interface. The numeric results were correlated to the experimental fatigue data of threaded components with and without the nut interface, to allow the oil & gas companies to extrapolate the results for different thread dimensions, since the experimental tests are not feasible to be performed for all thread interfaces. Scanning electron microscopy (SEM) was used to analyze the fracture surfaces. The stress concentration factor had a greater influence on the fatigue performance of threaded components than the effect of the Cd and Zn-Ni coatings. The fatigue life of studs reduced by about 58% with the nut/stud interface, compared to threaded components without nuts. The elastoplastic FEA results showed that studs with a stud/nut interface had higher stress values than the threaded specimens without a nut interface. The FEA results showed that the cracks nucleated at the regions with higher strain, absorbed energy, and stress concentration. The substitution of Cd for a Zn-Ni coating was feasible regarding the fatigue strength for threaded and smooth components.
... However, central wavelength stability of FBGs after metallization is ignored by most of the researchers. According to the previous study, residual stress could be produced during the processes of plating [20], which could cause the fluctuation of centre wavelength [21]. Accordingly, the centre wavelength stability of FBGs after metallization should be systematically studied. ...
... The bare FBG with the temperature sensitivity of 9.50 pm/ • C was used as the reference. Before determining the centre wavelength stability of zinc coated FBGs, the zinc coated FBG was heat treated for reducing the residual stress produced in the plating, which has been depicted in detail in the previous study [20]. After that, zinc coated FBG and the reference bare FBG were placed on an optical platform with the ambient temperature of 23.0 • C, and centre wavelength shifts of the FBGs were recorded by a FBG Network Analyzer (Model FONA-2004B). ...
... Moreover, the Zn-Ni alloys obtained from aqueous solution are mostly mixture of intermetallic phases. [6][7][8][9] Ionic liquids (ILs) have aroused great concern as ideal alternative media for the electrodeposition of metals due to their distinct advantages, such as high ionic conductivity, wide electrochemical window, negligible vapor pressure, thermal stability, and excellent solubility for many metal salts. [10][11][12][13] It has recently been demonstrated that some zinc chloride-based ILs are suitable media for the electrodeposition of Zn-Ni alloy. ...
The electrodeposition behavior of Zn–Ni alloy on a Cu electrode has been studied in the choline chloride-urea-ethylene glycol (ChCl-urea-EG) based deep eutectic solvent (DES). The nickel and zinc sources are introduced into the solvent by the dissolution of nickel oxide (NiO) and zinc oxide (ZnO), respectively. Cyclic voltammetry indicates that the electroreduction of Ni(II) or Zn(II) species in the DES is a diffusion-controlled process and the diffusion coefficient of Zn(II) species is an order of magnitude larger than that of Ni(II) species. Under the examined condition, the anomalous codeposition of Zn–Ni alloy is observed, which is different from normal codeposition of Zn–Ni alloy in similar DESs using metal chlorides as precursor. The deposition potential is found to play an important role in controlling the composition and surface morphology of the resultant Ni-Zn alloys. The phase structure of the deposits depends on the Ni content, and changes from a mixture of η-phase and γ -phase to single γ -phase with (411) plane orientation. A mechanism for this electrodeposition process has been proposed on the basis of the formation of complex ions [NiO·urea·Cl] ⁻ , [ZnO∙urea·Cl] ⁻ and [ChCl·O·urea] ²⁻ in ChCl-urea-EG-ZnO-NiO electrolyte during the electrodeposition, emphasizing that the metal oxides were dissolve in DES by forming metal complex ions, the cathodic reduction of metal complex ions generates complex ions [ChCl·O·urea] ²⁻ with alloys (Ni x Zn y ), and [ChCl·O·urea] ²⁻ is oxidized to release O 2 at anode.
... Thus, the axial fatigue strength of the Cd coating condition remained the same. The main adverse effect of electroplated Cd coating is the possibility of hydrogen embrittlement, whose effect of decreasing the fatigue strength was observed in previous works (Ref 3,12). The hydrogen embrittlement can occur below the yield stress, with a subcritical crack growth above a threshold stress level, or between the yield stress and the ultimate tensile stress, with the fracture initiated either by microvoid coalescence or by a brittle fracture mode at the surface (Ref (28)(29)(30)(31)(32) HRC, and, therefore, the hydrogen embrittlement is less likely to happen. ...
The fatigue behavior of electrodeposited Zn-Ni alloy coating was investigated for its suitability to replace Cd coatings in AISI 4140 steel studs applied in oil and gas industries due to environmental and human health considerations. Axial fatigue tests were carried out at room temperature and statistically analyzed through two-parameter Weibull distribution. The coatings characterization included chemical composition and corrosion resistance analysis through energy-dispersive spectroscopy and salt spray tests, respectively. Furthermore, the fracture surfaces were observed using scanning electron microscopy, and the stress gradient in studs was obtained through finite element analysis. The experimental results showed that the notch sensibility was higher for high-cycle fatigue regime, varying from 0.20 to 0.61 for 104 and 105 cycles, respectively. The stress concentration effect influenced the fatigue life of the component, especially for low-stress levels, decreasing the fatigue strength in about 9% for 104 cycles and more than 20% for 105 cycles. The experimental fatigue data showed an increase in axial fatigue strength of about 8% for 105 cycles for electrodeposited Zn-Ni coating specimens, indicating feasibility with respect to fatigue behavior of the substitution of electrodeposited Cd for a Zn-Ni alloy.
... Coating homogeneity and strong adhesion with the substrate are observed (Voorwald et al 2005). The result reveals that the edges of the cuts are totally even with no detachment of any square of the lattice (Grade 5B). Figure 13 shows the image of Adhesion tested specimen. ...
... The decrease is more pronounced in case of monolayer when compared to the multilayer Zn-Ni alloy coatings. The thickness of the coatings is directly related to the high tensile residual internal stresses, which result from the presence of Ni in the alloy [31]. The drop in the coating thickness with the temperature may be attributed to the iron enrichment caused by the formation of intermetallic Zn/Fe compounds due to the inter-diffusion at the coating/substrate interface. ...
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Composition modulated multilayer alloy (CMMA) coatings of Zn-Ni were electrodeposited galvanostatically on mild steel (MS) for enhanced corrosion protection using single bath technique. Successive layers of Zn-Ni alloys, having alternately different composition were obtained in nanometer scale by making the cathode current to cycle between two values, called cyclic cathode current densities (CCCD’s). The coatings configuration, in terms of compositions and thicknesses were optimized, and their corrosion performances were evaluated in 5 % NaCl by electrochemical methods. The corrosion rates (CR)’s of multilayer alloy coatings were found to decrease drastically (35 times) with increase in number of layers (only up to 300 layers), compared to monolayer alloy deposited from the same bath. Surface study was carried with SEM, while XRD was used to determine metal lattice parameters, texture and phase composition of the coatings. The effect of heat treatment on surface morphology, thickness, hardness and corrosion behaviour of multilayer Zn-Ni alloy coatings were studied. The significant structural modification due to heat treatment is not accompanied by any decrease in corrosion rate. This effect is related to the formation of a less disordered lattice for multilayer Zn-Ni alloy coatings.
In the aeronautical industry, many critical components are made of high-strength steels. These steels have high tensile strength but are sensitive to corrosion and to the hydrogen embrittlement phenomenon. This study examines how acoustic emission could be used to detect hydrogen embrittlement of high-strength steels and reduce the duration of the standard test. Acoustic emission (AE) was coupled with sustained load testing at 75% of the material fracture stress for 200 h as prescribed in ASTM standard F519. Tensile strength tests were also conducted to determine the mechanical characteristics and acoustic signature of the mechanisms of damage that progress to material fracture. The results show that the time required for sustained load tests can be shortened, based on the emission of acoustic events by the hydrogen-embrittled test coupons from the beginning of the test and after certain lengths of time. Scanning electron microscopy imaging of the fracture surfaces showed a very good correlation with the recorded acoustic event signatures.
de Zinkbasierte Korrosionsschutzsysteme bieten dem Anwender eine günstige und dauerhafte Möglichkeit, Bauteile aus Stahl vor korrosivem Angriff zu schützen. Deshalb sind diese Systeme in vielen verschiedenen Varianten im Einsatz und Stand der Technik. Untersuchungen zeigen, dass zinkbasierte Korrosionsschutzsysteme bei zyklischer Beanspruchung Einfluss auf die zyklische Beanspruchbarkeit bzw. Ermüdungsfestigkeit haben können. Dieser Einfluss wird in aktuellen Bemessungsregelwerken nicht oder nur teilweise berücksichtigt. In diesem Paper wird der Einfluss auf die Ermüdungsfestigkeit und die Möglichkeit der rechnerischen Berücksichtigung verschiedener Korrosionsschutzsysteme bei der Auslegung gegen Werkstoffermüdung aufgezeigt. Translation abstract en Zinc‐based corrosion protection systems provide the user with a favorable and long‐ lasting opportunity to protect steel components from corrosion. Therefore, these systems are used in many different variants and are state of the art. Investigations show that zinc‐based corrosion protection systems can have an influence on the fatigue strength during cyclic loading. This influence is not or only partly taken into account in current design regulations. In this paper, the influence on the fatigue strength and possibilities to consider the influence in the design against material fatigue is shown.
High and low cycle fatigue tests were conducted on high-strength steel using four-point bending. The materials tested were ASTM A723 steel in the as-machined condition, grit-blasted condition, MIL-DTL-16232 heavy manganese phosphate-coated condition, and ASTM A1059 Zn-alloy thermo-diffusion coated (Zn-TDC). The ASTM A723 steel base material exhibits a yield strength of ~1000 MPa. The effects of the surface treatments versus uncoated steel were examined. The fatigue life of the Zn-TDC specimens was generally reduced on as-coated specimens versus uncoated or phosphate-coated specimens. Several mechanisms are examined including the role of compressive residual stress relief with the Zn-TDC process as well as fatigue crack initiation from the hardened Zn-Fe alloy surface layer produced in the gas-metal reaction. Additionally, the effects of corrosion pitting on the fatigue life of coated specimens are explored as the Zn-TDC specimens exhibit significantly improved corrosion resistance over phosphate-coated and oiled specimens.
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The microstructure and toughness of coarse grain zone (CGZ) and mixed grain zone (MGZ) for laser welded 960 MPa grade high strength steel joints were investigated by thermal simulation with a Gleeble-3500 thermal simulator. The results show that microstructure of the stimulated CGZ mainly consists of uniform interweaved lath martensite, and grain growth is not severe upon increasing the cooling time (t 8/5). Microstructure of the stimulated MGZ presents strip-like in low peak temperature, and small block martensite is formed on the grain boundary. However, in high peak temperature, the strip-like microstructure disappears and small block martensite presents net-like structure. The lath character for MGZ and CGZ is very obvious under TEM observation, and the average lath thickness of BM, MGZ, and CGZ is 100, 150 and 200 nm, respectively. The impact energy and microhardness of CGZ are higher than MGZ and reduce with increasing the cooling time. The fracture toughness deteriorating drastically for MGZ may be related with the formation of the mixture microstructure, in which the small block martensite is distributed in the shape of a network.
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One of the most interesting alternatives for replacement of hard chrome plating is tungsten carbide thermal spray coating applied by the high velocity oxy-fuel (HVOF) process which presents a safer, cleaner and less expensive alternative to chromium plating. The objective of this research is to compare the influence of the tungsten carbide-17cobalt (WC-17Co) coating applied by high velocity oxy fuel (HVOF) process with that of hard-chromium electroplating on the fatigue strength and abrasive wear of AISI 4340 steel.
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One of the most interesting alternatives for replacement of hard chrome plating is tungsten carbide thermal spray coating applied by the high velocity oxy-fuel (HVOF) process which presents a safer, cleaner and less expensive alternative to chromium plating. The objective of this research is to compare the influence of the tungsten carbide-17cobalt (WC-17Co) coating applied by high velocity oxy fuel (HVOF) process with that of hard-chromium electroplating on the fatigue strength and abrasive wear of AISI 4340 steel.
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A theoretical model has been developed to explain the variation of surface residual stress introduced by shot-peening with external plastic deformation, during a uniaxial tensile test. The model is based on the difference of yield stress values of the shot-peened surface layer and the remaining bulk material. It has been shown that the model fits well with experimental results obtained for the base metal and heat-affected zone of a 5.0Cr-0.5Mo steel.
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The wide range of possible applications for the portable X-ray apparatus with an air cooled double-anode X-ray tube are presented. The apparatus is provided with a stress measurement unit and focusing camera for phase analysis. The distinctive characteristics of the apparatus are a small weight (a 4 kg), fine focus ray tube, portability and ease of use for both laboratory samples and industrial components. In the present paper the technical characteristics of the equipment, the methodology and experimental results are described. The most important of these are the following: measurements of tensile force in pre-stressed steel cables in concrete, residual stress measurements in railway wheels, stress measurements at elevated (up to 3OO'C) temperatures and stress measurements in welded joints including stresses in the weld bead and heat affected zone.
Although zinc electrodeposits are widely used for protecting steel against corrosion, they are unacceptable in certain applications because of their tendency to grow whiskers, necessitating the substitution of more expensive, whisker-immune, pure nickel deposits. The use of a zinc-nickel alloy plated from an ammoniacal sulfate solution appears to be both immune to spontaneous whisker growth and up to seven times as corrosion-resistant as unalloyed zinc deposits of equal thickness. Deposits can be obtained over sufficiently broad ranges of solution temperature, nickel sulfate concentration, and cathode current density, making production applications worth considering.
This review correlates the deposition mechanism, structure and properties of zinc-rich nickel alloy electrodeposits with corrosion data. It is shown that zinc coatings are greatly improved in corrosion resistance by codepositing 11 to 14 percent nickel.
Increasingly stringent environment regulations have encouraged the development of cadmium alternatives. Zinc-nickel alloy coatings applied by a new electroplating process were better than cadmium and cadmium-titanium coatings with regard to corrosion protection characteristics during salt-spray tests, equal to cadmium in torque-tension tests, and had satisfactory low-hydrogen-embrittlement characteristics when plated on notched tensile specimens. The zinc-nickel alloy is considered a viable alternative to cadmium for plating aircraft and commercial steel parts.
Corrosion properties of pulse-plated Zn-Ni alloy coating on a steel substrate were investigated using the neutral salt-spray test (ASTM B 117-81) and the potentiodynamic polarization technique (ASTM G 5-82). Performance of these alloy coatings with various Ni contents (up to 62 wt%) was compared to that of laboratory-prepared electrodeposited Zn coatings and commercial galvannealed (GA) steel. Results of the neutral salt-spray test indicated corrosion resistance of pulse-plated Zn-Ni alloy coatings was superior to that of the pure Zn and commercial GA coating. The Zn-20 wt% Ni and Zn-14 wt% Ni alloys gave the best protection of the Zn-Ni coatings tested. Potentiodynamic polarization tests confirmed excellent corrosion performance of the 20 wt% Ni alloy
The results of electrochemical experiments and simple corrosion studies conducted on several Zn-Ni and Zn-Co alloy coatings with different phase structures and compositions are presented. Experimental studies exploring the dezincification and sulfidation behaviors of optimized dual-layer coatings consisting of a Zn-5wt.%Ni or Zn-1wt.%Co alloy underlayer and a thinner Ni-22wt.%Zn alloy surface layer, are also described. The results are discussed and compared with those of similar studies conducted with Cu-35wt.%Zn brass strips. Such qualitative comparisons illustrate the improved corrosion resistance and the retention of a high level of adhesion to natural rubber compounds of the new dual-layer coating system in a corrosive environment.
Shot-peening is a surface treatment for metals largely used to increase their fatigue resistance. According to some authors, shot-peening gives rise to residual compressive stress in the surface layers of the metals, which could explain the fatigue resistance improvement. This is quite reasonable as this compressive stress reduces the net effect of the tensile component of the applied cyclic loading. This effect increases the fatigue resistance. There is however another point of view on this subject that ascribes less importance to the residual compressive stress influence. It is based upon work which shows that cyclic loading promotes residual surface stress modification by a mechanism of local plastic microdeformation. Since in this case a surface stress decrease would occur, these papers report that in the early applied cycles, residual stress could not have any influence on the ultimate fatigue behavior of the metal. This point of view highlights the need for a study to clarify the influence of plastic deformation upon relaxation as a function of variation of the initial surface residual stress. The aim of the present work is to provide a better understanding of these questions. Steel samples of 5Cr-0.5Mo (weight percent) were submitted to shot-penning in order to build up compressive surface residual stress. The samples were plastically deformed by uniaxial tensile test until complete fracture. Longitudinal and transverse residual stresses were measured before and during the test.