Fretting-wear Research Articles

FRET-ting over Inactivation

FRET-ting over Inactivation

Effects of ultrasonic surface rolling processing and plasma nitriding on the fretting wear behavior of Inconel 690TT

Inconel 690TT has been applied to steam generator for transport tube, which fretting wear (FW) will cause serious damage on it. In this work, the ultrasonic surface rolling processing (USRP), plasma nitriding (PN) and ultrasonic surface rolling processing combined with plasma nitriding process (USRP+PN) are applied for improving the fretting wear behavior of Inconel 690TT. The results show that a high fraction of grain boundaries is induced after the USRP. Compared to the untreated specimens, the surface hardness of specimen treated by the USRP, PN and USRP + PN increased by 191%, 295% and 348%, respectively. It can be attributed that the USRP can improve the surface hardness by the gradient nanostructure (GNS) layer, and the PN process can enhance the surface hardness by changing the chemical composition near the top surface. After the USRP, PN and USRP+PN, the wear volume decreased by 72%, 86%, 96%, respectively. It indicated that the surface fretting wear resistance by benign effect between processes can be arranged as USRP+PN > PN > USRP > untreated, which can provide a potential way to improve the surface fretting wear resistance of Inconel 690TT.

On the Role of Contact and System Stiffness in the Measurement of Principal Variables in Fretting Wear Testing.

In this work, the role of the contact stiffness in the measurement of principal variables in fretting wear tests is assessed. Several fretting wear tribometers found in the literature, including one developed by the authors, are analysed and modelled using numerical methods. The results show the importance of the tribosystem stiffness and tangential contact stiffness in the displacement sensor calibration and in the correct numerical modelling of fretting wear tests, especially for flat-to-flat contact configuration. The study highlights that, in most cases, direct comparisons between fretting results with severe wear obtained with different tribometers cannot be performed if the contact stiffness is not properly considered during the development of the experiments.

Soft and thick DLC deposited on AISI 316L stainless steel with nitriding as pre-treatment tested in severe wear conditions

Thick and soft DLC coatings were deposited over stainless steel to improve their surface properties, protecting them from wear in different conditions. When a protective film is thick, it can be considered as self-sustaining in terms of load-carrying capacity during wear situations even if the substrate is soft or hard. Thin and hard DLC coatings are well known for having high hardness and low friction coefficient; however they have adhesion problems when deposited on soft steels and many of their wear properties also depend on adhesion. For this reason, a previous plasma nitriding process may be convenient. In this work, the fretting and erosion wear behaviour of DLC soft coatings deposited on nitrided and non-nitrided austenitic stainless steel was evaluated using high loads and long tests both simulating severe conditions wear. The aim is to analyse under which conditions the film thickness is not enough to withstand wear damage when deposited onto soft steels. The results showed that in the fretting tests, the duplex sample presented better resistance than the only coated sample in all tested conditions, except for the minimum load, 12 N. In slurry erosion tests, the mass loss was similar in both samples until nine hours, when the influence of the nitrided layer became noticeable as a hard layer since the coating partially removed.

Influence of soft interlayers on fretting fatigue and fretting wear resistance of Ti-6Al-4V alloy

Ti-6Al-4V alloy is the main structure material of aerospace components due to its excellent corrosion resistance, high specific strength and other good characteristics. However, this alloy has low hardness, poor wear resistance and higher friction coefficient, so it is very sensitive to fretting wear (FW) and fretting fatigue (FF) damages. In this work, we studied three kinds of soft inter-layers (copper foil, nickel foil and polytetrafluoroethylene (PTFE) lamella) between the Ti-6Al-4V fatigue samples and the Ti-6Al-4V counterparts respectively to enhance the FF and FW resistance of this alloy. The results show that the method is an economical and effective way to increase the FF and FW resistance of Ti-6Al-4V alloy. The order of enhancement in the FF resistance of the titanium alloy was copper foil > PTFE lamella > nickel foil. Additionally, the friction coefficients of PTFE lamella, copper foil, nickel foil and Ti-6Al-4V alloy were about 0.10, 0.60, 0.65 and 1.1, respectively. The lowest friction coefficient of PTFE, compared with copper foil, nickel foil and substrate, was of great benefit to improving the FF property of Ti-6Al-4V alloy. Nevertheless, the FF life of Ti-6Al-4V alloy with the copper interlayer was higher than PTFE, which was about 5 times higher than substrate.

Micromotion at the head-stem taper junction of total hip prostheses is influenced by prosthesis design-, patient- and surgeon-related factors

Taper junctions of modular hip prostheses are susceptible to fretting and crevice corrosion. Prevalence and significance increase for cobalt-chromium heads assembled on titanium-alloy stems. Retrieval and in-vitro studies have identified micromotion between the taper components to accelerate the corrosion process. The aim of this study was to identify the most critical factors contributing to increased micromotion, which is most likely influenced by design-, patient- and surgeon-related aspects. Micromotion between head and stem taper surfaces was measured for different taper surface topographies and load orientations. Consecutive visual images were recorded through windows in the head component. By image matching analysis the local micromotions at the taper junction between head and stem tapers were determined. To extend the findings to taper regions not visible through the windows, finite element models were generated. The models were further utilized to investigate the influence of head length, taper angle difference and assembly force on micromotion. Significantly higher micromotion (+20%) was found under varus loading (7.1 µm) in comparison to valgus loading (5.9 µm). Smooth and microgrooved stem tapers exhibited equal amounts of micromotion. The numerical model revealed head tilting and recurring taper contact changes in terms of cyclic engagement/disengagement during the loading sequences. Especially long heads (+240%) and low assembly forces (+53%) were found to substantially increase micromotion (from 2.7 µm to 9.3 µm and from 4.1 µm to 8.8 µm, respectively). This study accentuates the susceptibility of taper junctions to a variety of factors, which need to be appreciated in preoperative planning and surgical procedure to reduce the amount of micromotion and such minimize the risk of critical corrosion.

Effects of T6 Heat Treatment on Fretting Wear Resistance of the Aluminum-Silicon Alloys

It is well known that damage caused by wear and tear of the mechanical parts always seriously affect the accuracy of machinery. It is very important to improve the material properties of the mechanical elements. Anti-abrasion can improve the durability of machinery and equipment, thereby enhancing industrial competitiveness. Hence, it is important to establish the key technology of wear resistance for the related industries. Since the aluminum-silicon alloys are commonly used on the conditions of severe fretting wear, it is necessary to improve the fretting wear resistance before they are used. Therefore, effects of T6 heat treatment on fretting wear resistance of the aluminum-silicon alloys were investigated in this study. The experimental results of this paper will be very beneficial to the future of precision machinery and vehicle industry to develop more internationally competitive products.

Fretting initiated crevice corrosion of 316LVM stainless steel in physiological phosphate buffered saline: Potential and cycles to initiation

Mechanically assisted crevice corrosion (MACC) has been associated with implant failure in vivo and is a serious concern in numerous metallic implant systems. Stainless steel medical devices may be subjected to fretting and crevice corrosion in the human body as are titanium and CoCrMo alloys due to the presence of a passive oxide film on their surface. One mechanism of MACC that has not been clearly identified and studied is fretting-initiated crevice corrosion (FICC) of stainless steel where an initial fretting event can initiate a rapid propagating crevice corrosion process even when fretting has ceased. FICC pin-on-disk experiments were performed at varying potential conditions and duration of fretting to explore the role of potential and fretting duration on the initiation of crevice corrosion. Triggering of a propagating crevice corrosion reaction on stainless steel at 250 mV vs Ag/AgCl/KCl (saturated) in PBS solution required only 2 s (2 cycles at 1 Hz) of fretting. Crevice corrosion continued to propagate under a 1.8 mm diameter pin with only 100 μm of direct contact, dissolving in both the depth and width dimension away from the fretting contact while the currents rose from 0.2 μA to 15 μA within 5 min. Three different potential-dependent FICC regions were identified that included unstable crevice corrosion (50 mV and above), metastable crevice corrosion (−100 mV to 0 mV) and stable fretting corrosion (between −500 mV and −150 mV). Crevice corrosion can be induced by fretting at potentials as low as −100 mV. Below −100 mV, there was no FICC, but rather fretting corrosion stopped immediately after fretting ceased and returned to a stable baseline current. Metastable FICC was shown at potentials between −100 mV and 0 mV, when the crevice corrosion current gradually decreased over several seconds or longer after fretting ceased. Self-sustained, unstable crevice corrosion started at 50 mV, where prior to fretting the currents were low, and after just a few cycles of fretting the crevice current rose rapidly and continued to increase after fretting stopped. Increase of potential increased the susceptibility of stainless steel to FICC. Scanning electron microscopy and digital optical microscopy revealed pitting and crevice corrosion on samples at −100 mV and higher potentials, where FICC was developing. By removing the oxide film, fretting motion significantly facilitates the critical crevice solution development, lowering the critical crevice potential and decreasing the initiation time for crevice corrosion. These results indicate that fretting initiated crevice corrosion may affect the performance of stainless steel in vivo. Statement of SignificanceAISI 316L stainless steel has been widely used as a metallic biomaterial for orthopaedic, spinal, dental and cardiovascular implants. Crevice corrosion has been a serious concern for stainless steel implants. For the first time we demonstrated and systematically studied the process of fretting-initiated crevice corrosion (FICC) in 316L stainless steel in simulated physiological solution of phosphate buffered saline. By removing the oxide film, fretting motion significantly facilitates the critical crevice solution development, lowering the critical crevice potential and decreasing the initiation time for crevice corrosion. Our findings indicate fundamental differences between the FICC mechanism and conventional crevice corrosion theory, showing that fretting can play a significant role in the initiation of crevice corrosion of stainless steel.

FRETTING FATIGUE BEHAVIOR OF COMBINED PLASMA ZIRCONIUMING AND SHOT PEENING ON Ti6Al4V ALLOY

Low wear resistance and high sensitivity to fretting fatigue (FF) damage limit the application of titanium alloys. In order to improve its wear resistance, surface plasma Zirconium (Zr) alloying is a candidate through solution strengthening with its property of infinite solid solution with [Formula: see text]–Ti and [Formula: see text]–Ti. In this work, the plasma Zr metallurgy technique was used to improve the FF resistance of Ti6Al4V alloy combined with shot peening (SP), which is different from the combined treatments of the surface modification with high hardness and SP, and may explain the impacts of ductility and strength in improving FF resistance. The results indicate that the Zr metallurgy layer is composed of a Zr–Ti solid solution with low surface hardness and density, which induce the reduction of the fretting wear (FW) resistance and FF resistance of the Ti6Al4V alloy. Instead, when SP was used as the post treatment, the FW and FF behavior of the titanium alloy were increased obviously after prior plasma Zr metallurgy, especially to high cycle fatigue. This indicates that residual stress introduced by SP is beneficial for improving both FW and resistance.

A coupled crack initiation and propagation numerical procedure for combined fretting wear and fretting fatigue lifetime assessment

This work presents a numerical procedure for combined fretting wear and fretting fatigue problems. It combines the Archard wear model and the Smith-Watson-Topper fatigue indicator parameter with the Miner damage rule for crack nucleation estimation. The eXtended Finite Element Method (XFEM) is then used in combination with the Archard wear model for crack propagation prediction. This procedure was validated in 12 experimental tests taken from the literature, and a good correlation was found. The procedure allows a detailed study of the interaction between the crack and fretting contact in combination with wear. The results show that the relative slip decreases and changes its distribution unevenly when the crack grows, and highlight the key importance of accounting for wear in order to obtain non-conservative predictions.

Does Taper Design Affect Taper Fretting Corrosion in Ceramic-on-Polyethylene Total Hip Arthroplasty? A Retrieval Analysis

BackgroundCeramic-on-polyethylene (CoP) implants have exhibited lower fretting and corrosion scores than metal-on-polyethylene implants. This study aims at investigating the effect of taper design on taper corrosion and fretting in modular CoP total hip arthroplasty (THA) systems. MethodsUnder an institutional review board–-approved protocol, a query of an implant retrieval library from 2002 to 2017 identified 120 retrieved CoP THA systems with zirconia toughened alumina femoral heads. Femoral stem trunnions were visually evaluated and graded for fretting, corrosion, and damage at the taper interface. Medical records were reviewed for patient demographics and implant characteristics. Data were statistically analyzed using Spearman correlation and rank-sum tests with a Dunn’s post hoc test, with a significance level of α = 0.05. ResultsFour different taper designs were evaluated: 11/13 (n = 18), 12/14 (n = 53), 16/18 (n = 21), and V40 (n = 28). There were no statistically significant demographic differences between taper groups for duration of implantation, laterality, patient age, and patient sex, but patients with 16/18 tapers had a higher body mass index than V40 tapers (P = .012). Duration of implantation had a weak positive correlation with both trunnion fretting (ρ = 0.224, P = .016) and corrosion (ρ = 0.253, P = .006). Summed fretting and corrosion scores were significantly greater on the V40 and 16/18 tapers compared with the 12/14 tapers (all P ≤ .001). ConclusionTaper fretting and corrosion were observed in CoP THA implants and were greatest with V40 and 16/18 tapers and lowest with 12/14 tapers. Differences in taper design characteristics may lead to greater micromotion at the taper-head interface, leading to increased fretting and corrosion.

A modelling approach for the nonlinear dynamics of assembled structures undergoing fretting wear.

Assembled structures tend to exhibit nonlinear dynamic behaviour at high excitation levels due to the presence of contact interfaces. The possibility of building predictive models relies on the ability of the modelling strategy to capture the complex nonlinear phenomena occurring at the interface. One of these phenomena, normally neglected, is the fretting wear occurring at the frictional interface. In this paper, a computationally efficient modelling approach which enables considerations of the effect of fretting wear on the nonlinear dynamics is presented. A multi-scale strategy is proposed, in which two different time scales and space scales are used for the contact analysis and dynamic analysis. Thanks to the de-coupling of the contact and dynamic analysis, a more realistic representation of the contact interface, which includes surface roughness, is possible. The proposed approach is applied to a single bolted joint resonator with a simulated rough contact interface. A tendency towards an increase of real contact area and contact stiffness at the interface is clearly observed. The dynamic response of the system is shown to evolve over time, with a slight decrease of damping and an increase of resonance frequency, highlighting the impact of fretting wear on the system dynamics.

Determination of local micromotion at the stem-neck taper junction of a bi-modular total hip prosthesis design

High rates of clinical complications with bi-modular hip prostheses are attributed to failure of the stem-neck taper junction. Taper wear analyses have shown extensive material loss as a result of corrosion, potentially initiated by micromotion. The purpose of the study was to determine the amount of micromotion at this junction for different loading, assembly and material conditions.Micromotion between the neck adapter (CoCr29Mo6-alloy) and the stem (TiMo12Zr6Fe2-alloy; both Rejuvenate, Stryker) within the taper junction of a bi-modular hip stem were determined by image matching analysis of consecutively recorded images through windows in the stem component. A finite element model was used to determine the micromotion in the taper regions outside the windows and validated with the measured micromotion. With the model, the influence of the load amplitude, assembly force and component materials were then investigated. Determined micromotion (14–79 µm) by far exceeded critical values (5 µm) associated with the onset of fretting corrosion. Increasing assembly forces achieved a significant reduction in micromotion. The numerical model revealed insufficient assembly to cause the neck to perform rocking motions under load, repetitively changing taper contact in combination with gap opening, which facilitates fluid ingress into the junction. Changing the stem material to a stiffer Ti-alloy achieved a reduction of the micromotion of about 30%. This study emphasises the high importance of material selection, assembly force and loading on the susceptibility of bi-modular hip stems to fretting and crevice corrosion. These findings can serve to explain the increased rate of clinically reported problems with this particular prosthesis design.

Materials Solutions to Address High Temperature Fretting Wear in Gas Turbine Combustor Components

Structural parts like combustor and its components plays an important role in the overall performance of a land based heavy duty gas turbines. Due to system dynamics and poor material combinations, these parts undergo severe wear leading to durability issues and even part failures. Parts like liners, burners, transition piece and seals are free to undergo small amplitude motion and lead to fretting and related wear. In many situations, these component surfaces are un-coated or not protected from the severe degradation. The objective of this work is to develop a robust coating system to mitigate fretting and related wear under elevated temperature. A molybdenum rich-cobalt based tribaloy-800 is used to address the wear issues and studied in greater details. Tribaloy-800 multilayer coating is deposited on Nickel base alloy by HVOF coating process to achieve maximum distribution of laves hard phase. Further, coating is heat treated under vacuum furnace to optimize the microstructure which is desirable to work on these harsh operating conditions. A custom built fretting wear setup was used to perform gross-slip wear test, as standard laboratory experiments may not simulate the field wear mechanisms better. Both uncoated and coating materials were studied at elevated temperature (550 °C) under constant stress up to 3 million cycles to produce steady state wear rate. Fretting wear data reveals severe galling type of wear mechanisms in uncoated materials lead to fast removal material from the surface. Both as-coated and heat-treated coatings produced better wear resistance under same test conditions compared to uncoated nickel alloy. Heat treated tribaloy-800 coating shows crystalline rich laves phase distribution lead to superior wear performance.

Investigation of shot peening combined with plasma-sprayed CuNiIn coating on the fretting fatigue behavior of Ti-6Al-4V dovetail joint specimens

Dovetail joint specimens manufactured from the Ti-6Al-4V alloy were designed and used to investigate the fretting fatigue behavior of the blade/disk interface in gas turbine engines. Shot peening was combined with plasma-sprayed CuNiIn coating to improve the fretting fatigue resistance of the specimens. The finite element models were used to analyze the contact stress distribution in the fretting area. A plastic layer was added to simulate the CuNiIn coating that was sprayed on the surface of the dovetail blade. The fretting cracks tended to initiate at the contact edge, where the high stress concentration existed, and severe fretting wear damage occurred. The CuNiIn coating modified the local stress distribution under the fretting condition and mitigated the stress concentration degree of the contact edge. The surface strain hardening layer and the compressive residual stress were induced by the shot peening treatment, which promoted the wear and the fatigue resistance of the Ti-6Al-4V substrate under the fretting condition. The fretting fatigue property of specimens improved after the combined surface treatment.

Finite element simulation of the influence of fretting wear on fretting crack initiation in press-fitted shaft under rotating bending

A Finite element based methodology for fretting wear and fretting fatigue prediction in press-fitted shaft is developed. This methodology integrates wear modelling with fretting fatigue analysis to quantitatively predict of the effects of stress redistribution and material removal induced by the fretting wear on fretting crack initiation properties. The fretting wear-induced evolutions of mean normal stress, a mean correction multiaxial damage parameter and accumulated fatigue damage are predicted by this methodology. The results show that the fretting crack initiation at the contact edge is significantly suppressed by the severe fretting wear, since the server stress concentration is relieved and the surface material with high accumulated fatigue damage is grinded off. While, the fretting crack initiation at the inner surface of the contact area is greatly promoted by the slight wear by introducing the large stress concentration near the edge of fretted wear scar.

Enhanced Corrosion and Wear Behavior of Nano Titanium Carbide Reinforced Polyurethane PMC Coating on Aluminium 7075

Aluminum 7075 has an extensive variety of utilization over different fields because of its intrinsic properties such as high ductility, high toughness, high strength and low density. It is being utilized broadly for structural parts in aviation industries to manufacture aeroplane wings, internal bearing and fuselage. In spite of having high strength to weight ratio, aluminium does not have good resistance against wear and corrosion.Surface coating technology is a well-known technique for improving the wear resistance and corrosion resistance of the coated substrate which can eliminate corrosion along with fretting and adhesive wear by providing suave surface..Generally, polyurethane (PU) coatings were done on engineering metals to provide corrosion protection; hence it is highly advantageous to coat it on aluminium 7075 to improve its corrosion resistance.Polyurethane coating technology offers excellent adhesion and corrosion resistance when compared with other traditional metal coatings such as electro plating, electroless plating, PVD, CVD etc. Polymer Matrix Composite (PMC) coatings were preferred to improve the wear resistance along with corrosion resistance on corrosive and low wear resistant metals such as copper alloys, mild steel, and aluminum alloys. In this paper, PMC coatings of polyurethane as matrix along with nano titanium carbide reinforcement were coated on Aluminium 7075 through physical deposition method. The nano TiC was blended with Epoxy polyamide (EP) and Polyurethane separately in different proportions (1%, 2% and 3%) with the help of mechanical stirrer. Epoxy polyamide along with TiC nano composite was first coated as a base coat on the Aluminium 7075 substrate at the pressure not exceeding 35bar. The polyurethane was coated as top coat along with nano titanium carbide as reinforcement on Aluminium 7075 in different volume percentage. Wear, corrosion and optical microscope studies were done. Micro hardness test reveals that the sample which was coated with 3% nano TiC along EP and 3% nano TiC & PU gives the highest hardness when compared to other samples. It is attributed to the fact that it contains the highest percentage of titanium carbide mixed to both the polyurethane and the epoxy polyamide when compared to the other samples which has nano TiC in either base coat or upper coat. Similarly, through salt spray test it was found that highest corrosion resistance was observed in the sample which was coated with nano TiC in both the EP and PU. The samples were also examined through optical microscope and test results were justified. The inclusion of nano titanium carbide to the polymer coating increases the coating hardness, wear resistance and corrosion resistance of the aluminium 7075.

Reducing fretting-initiated crevice corrosion in hip simulator tests using a zirconia-toughened alumina femoral head.

Taper fretting corrosion is considered a potentially limiting factor for total hip arthroplasty longevity. Recently, attention has been focused on new materials for ceramic femoral heads, for example, zirconia-toughened alumina (ZTA), since they have an alternative bearing surface that can improve the wear resistance. Moreover, ceramics have high chemical stability and corrosion resistance. In this study, we evaluated the effects of ZTA and Co-Cr-Mo alloy femoral heads on their taper fretting and/or corrosion characteristics under a controlled hip simulator test. After the test, less fretting and corrosion were observed in the taper surface of the trunnion against the ZTA femoral head than for that against the Co-Cr-Mo alloy femoral head. In addition, corrosion damages were only observed in the lateral-distal taper surface (noncontact area) of the trunnion in the Co-Cr-Mo alloy femoral head group. The ZTA femoral head group also eliminated the potential for Co ion release into the lubricants from taper corrosion, reducing the possibility of adverse local tissue inflammatory responses. In conclusion, ZTA femoral heads showed markedly less fretting corrosion compared to Co-Cr-Mo alloy femoral heads and have a lower potential for metal ion release. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2815-2826, 2018.

Fretting and Corrosion Damage in Retrieved Metal-on-Polyethylene Modular Total Hip Arthroplasty Systems: What Is the Importance of Femoral Head Size?

BackgroundFretting and corrosion at the modular femoral head-femoral neck (taper) interface have been reported in retrieved total hip arthroplasty (THA) prostheses. This study investigated associations among implant design, radiographic factors, and patient factors with corrosion and fretting at the taper interface in retrieved metal-on-polyethylene modular THA prostheses. MethodsNinety-two retrieved primary metal-on-polyethylene THA implants were evaluated and graded for fretting, corrosion, and damage at the taper interface, including the femoral stem trunnion and femoral head. Preoperative radiographs were assessed for osteolysis and femoral stem alignment; and medical records were reviewed for demographic data. ResultsMale patients had greater head corrosion (P = .037), patient age at revision had a weak, negative correlation with trunnion corrosion (ρ = −0.20, P = .04), and both body mass index and duration of implantation had weak, positive correlations with head fretting (ρ = 0.26, P = .01 and ρ = 0.33, P = .001, respectively). A weak, negative correlation was found between femoral head size and both head fretting and head corrosion (ρ = −0.26, P = .007 and ρ = −0.21, P = .028, respectively), and a weak, positive correlation was found between head offset and trunnion fretting (ρ = 0.23, P = .030). Varus femoral stem alignment was associated with greater head fretting (P = .038). ConclusionLarger femoral head sizes were correlated with less severe head corrosion and head fretting, with 28-mm heads exhibiting more moderate-to-severe damage. Other factors, such as head-taper engagement and geometry, rather than head size, may affect rates of corrosion and fretting damage at the taper interface.

Fretting Wear Behaviors of Aluminum Cable Steel Reinforced (ACSR) Conductors in High-Voltage Transmission Line

This work reports the fretting wear behavior of aluminum cable steel reinforced (ACSR) conductors for use in high-voltage transmission line. Fretting wear tests of Al wires were conducted on a servo-controlled fatigue testing machine with self-made assistant apparatus, and their fretting process characteristics, friction force, wear damage, and wear surface morphology were detailed analyzed. The results show that the running regime of Al wires changes from a gross slip regime to a mixed regime more quickly as increasing contact load. With increasing amplitudes, gross slip regimes are more dominant under contact loads of lower than 30 N. The maximum friction force is relatively smaller in the NaCl solution than in a dry friction environment. The primary wear mechanisms in dry friction environments are abrasive wear and adhesive wear whereas abrasive wear and fatigue damage are dominant in NaCl solution.