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This study aimed to investigate the impact fretting wear behavior of thin-walled tubes under different support interfaces with a novel impact wear testing rig. A tube/cylindrical contact model was used, and V-shaped fixtures with varied angles were applied. The 304 stainless steel tubes with varied lengths and a GCr15 bearing steel roller were used as the test materials. The interface deformation, impact energy absorption, and damage behavior were investigated in terms of the influence of the support angle, tube length, and the initial impact energy. After the test, the wear mechanism of the tube was investigated. The results showed that under the same lengths, when the support angle increased, the deformation displacement increased, but the contact peak force, energy absorption, and the area of worn scars decreased. The increasing length increased the contact force, energy absorption ratio, and serious damage but reduced the deformation. The increasing kinetic energy of the initial impact will decrease the energy absorption ratio. Contact fatigue spalling and oxidation are the wear mechanisms of the impact fretting wear of 304 stainless steel. [ABSTRACT FROM AUTHOR]

Abstract: Ti6Al7Nb is a high-strength titanium alloy used in replacement hip joints that possesses the excellent biocompatibility necessary for surgical implants. Ti6Al7Nb treated with nitrogen gas (N2) plasma immersion ion implantation–deposition (PIII–D) was investigated. Torsional fretting wear tests of untreated and nitrogen-ion-implanted Ti6Al7Nb alloys against a Zr2O ball (diameter 25.2mm) were carried out under simulated physiological conditions (serum solution) in a torsional fretting wear test rig. Based on the analyses of the frictional kinetics behavior, the observation of 3D profiles, SEM morphologies and surface composition analyses, the damage characteristics of the surface modification layer and its substrate are discussed in detail. The influence of nitrogen ion density on the implantation and torsional angular displacement amplitudes were investigated. The results indicated that ion implantation layering can improve resistance to torsional fretting wear and thus has wide potential application for the prevention of torsional fretting damage in artificial implants. The damage mechanism prevented by the ion implantation layer on the Ti6Al7Nb alloy is a combination of oxidative wear, delamination and abrasive wear. An increase in ion implantation concentration inhibited detachment by delamination. [Copyright &y& Elsevier]

Abstract: Detailed fretting wear phenomena are usually hidden between the two compact contact interfaces. Direct or in situ observation of fretting wear is supposed to obtain time-dependent damage information. In this paper, the torsional fretting wear tests of plymethyl methacrylate (PMMA) flat against AISI 52100 steel spheres had been investigated on an improved test rig, which provides the real-time in situ observation, friction vibration and noise measurements. The running behaviours (frictional kinetics characteristics), wear mechanisms, oxidative behaviours and debris behaviours of the torsional fretting contact interfaces in combination with the friction vibration analyses were analyzed in detail. The results of observation suggested that a slight damage could be found in the partial slip regime. And the spindle-like detachment occurred in the mixed fretting regime, which presented a radial pattern distribution in the wear scar. The friction lateral vibration decreased accompanied with the accumulation of the debris, and the appearance of third-bodies helped to reduce the friction vibration. In the mixed fretting regime and slip regime, the wear mechanisms mainly were fatigue wear and oxidative wear. [Copyright &y& Elsevier]

Abstract: A torsional wear and friction simulator with a ball on flat polymer was developed to analyze the tribological behavior of hip joints. Wear tests of polymethyl methacrylate (PMMA) against GCr15 (AISI 52100) steel and PMMA molecules (both with diameters of 40mm) were conducted. Based on the analysis of frictional kinetics behaviors, and observations of three-dimensional (3D) profiles and SEM morphologies, the damage characteristics of PMMA were discussed in detail. With the increases of angular displacement amplitude, three types of torque/angular displacement amplitude (T–θ) curves (i.e., linear, parallelogram, and elliptical loops) were observed during the process of torsional fretting wear. In each of these loops, PMMA ran in a partial slip regime (PSR), mixed slip regime (MSR), and gross slip regime (SR), respectively. Compared to the PMMA/PMMA (P/P) counter-pairs, the boundary of the fretting regime of PMMA/GCr15 (P/G) counter-pairs shifted toward the direction of lower angular displacement amplitudes. The wear mechanisms of P/G counter-pairs included fatigue wear, oxidative wear, and adhesive wear; however, only abrasive wear was found for the P/P counter-pairs. [ABSTRACT FROM AUTHOR]

Abstract: Four simple fretting modes are defined according to relative motion: tangential, radial, rotational, and torsional fretting. This paper presents a new test rig that was developed from a low-speed reciprocating rotary system to show torsional fretting wear under ball-on-flat contact. Torsional fretting behavior was investigated for LZ50 steel flats against AISI52100 steel balls under various angular displacement amplitudes and normal loads. The friction torques and dissipation energy were analyzed in detail. Two types of T–θ curves in the shape of quasi-parallelograms and ellipticals were found that correspond to gross and partial slips, respectively. The experimental results showed that the dynamic behavior and damage processes depend strongly on the normal loads, angular displacement amplitudes, and cycles. In this paper, the debris and oxidation behaviors and detachment of particles in partial and gross slip regimes are also discussed. Debris and oxidation are shown to have important roles during the torsional fretting processes. The wear mechanism of torsional fretting was a combination of abrasive and oxidative wear and delamination before third-body bed formation. The mechanism was then transformed into third-body wear after a great amount of debris formed. [Copyright &y& Elsevier]

Abstract: Tests of LZ50 carbon steel against 52100 steel balls in ambient air (RH=60%) and in nitrogen were carried out on a controlled-atmosphere torsional fretting tribometer. The morphologies of worn scars were observed by a scanning electron microscopy (SEM), and the tribochemical behaviors of the contact zones were analyzed by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX). Curves of friction torques vs. torsional angular displacement amplitude (T–θ curves) were used to describe the kinetic behaviors of torsional fretting. According to the T–θ curves and damage morphologies, three fretting running regimes (partial slip regime, mixed regime, and gross slip regime) can be identified. Results indicated that the mixed and gross slip regimes shifted to higher angular displacement amplitudes in nitrogen, comparably to that in air. With an increase in the number of cycles, the curves of the friction torques can be divided into three stages: initial stage, climbing stage, and steady stage. The friction torque in nitrogen was much higher than in air, and the wear damage in nitrogen was also severer than that in air. The oxidative debris formed in air served as a lubricant and alleviated fretting wear. The torsional fretting wear mechanisms in the air were oxidative wear, delamination, and abrasive wear; however, the wear mechanisms in nitrogen were delamination and abrasive wear accompanied by a strong plastic flow due to the effect of tribo-oxidation being restrained. [Copyright &y& Elsevier]

• Effect of different copper graphite content ratio on the contact resistance was studied. • Relationship between surface atomic content and contact resistance was analysed. • The wear resistance and electrical contact endurance of different materials are compared. • The optimum proportion of copper/graphite materials is proposed. In this study, copper-graphite composites were prepared by powder sintering. The wear resistance and electrical contact endurance of composites with different copper-graphite ratios were investigated and are discussed. The results illuminate that the high electrical contact resistance evolution during fretting wear is related to the graphite content. With a decrease in the copper content, the interaction between graphite and copper increases, and the conductivity decreases. The graphite particles of the flat sample delaminate and form a graphite friction film between the contact surfaces; this friction film has excellent lubricating properties. Thus, the copper-graphite composites with the highest graphite content herein demonstrate good behavior against fretting wear and exhibit poor electrical contact performance. In other words, a relatively high copper content could maintain a decreased and stable contact resistance. The comprehensive performance of composite materials can be effectively developed by designing the copper-graphite ratio. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Graphene oxide/ZrO 2 coating on N36 Zr alloy was prepared and analyzed. • Corrosion and fretting wear behavior of graphene oxide/ZrO 2 coating was investigated. • The mechanism on improving corrosion and fretting wear behavior was investigated. ZrO 2 coatings combined with graphene oxide (GO) was prepared on N36 zirconium (Zr) alloy by micro-arc oxidation (MAO) technique. MAO coating shows a typical volcano-like structures with pores and cracks. The MAO coating with GO is composed with m-ZrO 2 and t-ZrO 2. The electrochemical test indicates that MAO coating provides good corrosion protection to Zr alloy, and corrosion resistance enhance significant with GO concentration increasing. The increasing in corrosion resistance is mainly due to that GO particles in the coating act as a barrier to the diffusion pathway of electrolyte and restrain aggressive electrolyte accessing to the substrate. Fretting wear test indicate that MAO coating with GO exhibits a lower coefficient of friction (COF) and wear volume compared with that of Zr alloy substrate and MAO coating without GO. Optimal concentration of GO in MAO coating is 0.05 g/L. Low COF and wear volume is attributed to the lubrication function of GO particle, and the lubrication of GO particle is caused by low shear stress of different GO layer. Wear mechanism of MAO coating with GO is mainly adhesive wear. Good corrosion and wear resistance prompt the MAO coating of Zr alloy becoming accident tolerant candidate cladding material used for reactor in nuclear power plant. [ABSTRACT FROM AUTHOR]

Torsional fretting corrosion in a physiological medium is one of the main reasons that artificial joints fail. In this study, we carried out experiments on torsional fretting corrosion in Titanium alloys (Ti6Al4V) against Zirconium dioxide (ZrO2) ceramic balls under 37°C in a Hank's simulated body fluid. During the tests, we recorded electrochemical corrosion parameters using an electrochemical analysis system in real-time. We analysed the torsional fretting dynamics behaviours, damage mechanisms, and electrochemical corrosion behaviours in detail using the micro-examinations of a scanning electron microscope (SEM), an energy-dispersive X-ray (EDX), a profilometer, and an X-ray photoelectron spectrometer (XPS). The results showed that the dynamics behaviours strongly depended upon the torsional angular displacement amplitude and the number of cycles. The friction torque increased with increases in the torsional angular displacement amplitude and normal load. We established a running condition fretting map (RCFM), which included three fretting running regimes: a partial slip regime (PSR), a mixed fretting regime (MFR), and a slip regime (SR). We determined that the influences of torsional fretting on electrochemical corrosion behaviours were strongly correlated to the angular displacement amplitude. Under large angular displacement amplitudes, the corrosion of the Ti6Al4V alloys in Hank's simulated body fluids were accelerated by torsional fretting, especially during the initial stage of the test. However, when the angular displacement amplitude was smaller than 1°, the corrosion potentials and corrosion currents were almost invariable during the entire duration of the test. The damage to the Ti6Al4V alloy was the result of wear and corrosion. The wear mechanisms were attributable to delamination and abrasive wear in the three fretting regimes. We observed almost no damage on the contact centre and only slight scratches and wear on the contact edge in the PSR. In MFR testing, the damage zone extended to the contact centre and the sticking zone (which exhibited no damage) contracted to the contact centre with increases in the number of cycles. Ultimately, in MFR and SR testing, the damage mechanisms were primarily the result of abrasive wear, oxidation wear, tribochemical reactions, adhesion wear, and electrochemical corrosion. [ABSTRACT FROM AUTHOR]

Salt layer preparation on the contact surface of Ti6Al4V dovetail joint specimens using solid NaCl and Na 2 SO 4 deposition, the effect of hot salt layer on fretting fatigue properties of Ti6Al4V alloy at high temperature was studied. The maximum stress load and temperature are 10 kN and 500 °C, respectively. The results show that the average fatigue life of the base metal dovetail joint sample (BM sample) is 9.93×104, and the average fatigue life of the hot salt dovetail joint sample (HS sample) is increased to 69.9×104. The increase in fatigue life stems from the fact that the hot salt layer promotes the generation of thicker loose oxides on the surface of the Ti6Al4V alloy, besides, the lubricating effect of the oxide with higher hardness and the wear debris alleviates the fretting damage between the dovetail joint sample and the contact surface of the fretting pad. Fracture analysis shows that the hot salt layer does not change the crack initiation mechanism, and all of them show single crack source propagation and ductile fracture mechanism. Analysis of crack formation zone by electron back-scattered diffraction (EBSD), it is found that the presence of less dislocation distribution in the HS sample relative to the BM sample. The dislocations are more concentrated on the crack propagation paths and the fretting fatigue contact surfaces. This indicates that the BM sample produced more significant plastic deformation in the crack formation zone, accelerating crack initiation. The contact surface plastic deformation of the HS sample is small and the fretting fatigue life is enhanced. • The salt-coated dovetail specimens designed for high-temperature fretting fatigue testing. • The salt-coated specimens had longer life under high temperature fretting fatigue test compared to the matrix specimens. • The mechanism of improved fretting fatigue life of salt-coated specimens relative to matrix specimens. [ABSTRACT FROM AUTHOR]

Grid-to-rod fretting (GTRF) is the main factor leading to the failures of fuel rods in reactor. The oxide layer formed on pre-wear stage has a significant impact on the wear resistance of zirconium (Zr) alloys fuel cladding. In this research, Zr alloy was immersed in high-temperature water conditions for 30 days,110 days,145 days, and 195 days. The characterization and fretting wear behavior of oxide layer on Zr alloy were investigated. Results show that the oxide layer consists of t-ZrO 2 , m-ZrO 2 , and metal Zr. The thickness and hardness of oxide layer increases with the corrosion time increase. The fretting running region and F-D curve are dependent on the oxide layer. Compared with Zr alloy, the wear volume of oxide layer on Zr alloy is significantly reduced because the structure of oxide layer is dense with a high hardness, leading to that the oxide layer is not easy to be destroyed during the fretting. The wear mechanism of Zr alloy is adhesive wear, and the wear mechanism of oxide layer is abrasive wear. • The fretting wear behavior of pre-oxidized Zr alloy cladding was investigated. • The wear volume of oxide layer on Zr alloy decreases with the corrosion time increase. • The fretting running region and F-D curve are significantly dependent on the oxide layer. [ABSTRACT FROM AUTHOR]

Abstract CoMoCrSi superalloy coatings were prepared on Mar-M247 Ni-based superalloy by high velocity oxygen fuel (HVOF) under various spraying parameters. Dense coatings with porosity < 0.8% were prepared, and the fretting wear properties of the coatings was investigated. The coatings showed good adaptability to the spraying parameters. As the temperature increased from R.T. to 400 °C, the friction coefficient of the coating decreased from 0.8 to 0.6, and the wear morphology gradually changed from pits to bulges. A large amount of material transfer occurred, and the main wear mechanisms at R.T. were abrasive wear and delamination; adhesive wear appeared slowly at elevated temperatures. The coating exhibited better wear resistance than the substrate during the experiments. Highlights • How the spraying parameters effect the fretting wear behavior of high velocity oxygen fuel (HVOF) coating was concerned. • The effect of temperature on the friction and wear properties of coatings has been studied. The friction coefficient decreases with increasing temperature, but the materials loss had the similar rule • The wear mechanism was abrasive wear and delamination in RT, and adhesive wear appeared slowly at elevated temperature. [ABSTRACT FROM AUTHOR]

In the heat exchangers of sodium-cooled fast reactors, sodium flow can cause the tubes to vibrate, resulting in fretting wear damage due to the contact between the tubes (2.25Cr-1Mo steel) and their support plate (Gr5C12 alloy). In this work, the effects of temperature on the fretting wear behavior of a 2.25Cr-1Mo heat transfer tube on a Gr5C12 alloy rod were studied. The results showed that the coefficient of friction (COF) and wear volume increased first and then decreased with the increase in temperature. Moreover, 2.25Cr-1Mo showed great wear performance at high temperatures than at room temperature and 80 °C, because of the antifriction nature of the oxidative layer and the high hardness of the tribological transformed structure layer. As the temperature increased, material transfer and plastic deformation became increasingly obvious, but average wear depth decreased. This provides data support for the practical engineering application of 2.25Cr-1Mo steel at elevated temperatures. Wear mechanisms were found to depend modestly on temperature and largely on normal load. As temperature increases, the wear mechanism gradually changes from abrasive wear to adhesive wear. [ABSTRACT FROM AUTHOR]

The fretting capabilities of 690 alloy against 405 stainless steel were evaluated through a series of tube-plate tests in different experimental conditions. The results indicated that as the temperature increased in air, the wear volume and wear depth increased first until reaching a maximum value at 90 °C and then decreased. This was attributed to spinel oxides formed above 200 °C in combination with adhesive wear, which contributed to oxidation resistance and a reduction of interfacial wear, resulting in the decrease of wear volume and wear depth. Metallic nickel, iron and chromium were observed in water, which indicated low oxidation, associated with lower wear damage. • Compared to air, unoxidized metal elements were observed in water, associated with lower oxidation and wear damage. • The testing environmental condition has a huge effect on the chemical state of chromium. • The spinel oxides and adhesive layer seemed to protect the surfaces and led to lower wear volume at 200 °Cand 285 °C. [ABSTRACT FROM AUTHOR]