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As a typical keratinous material, the mechanical properties of pangolin scales are affected by hydration. Clarifying the mechanism of influence of hydration on dynamic response of materials may provide valuable inspiration for bio-inspired design. In this study, mechanical properties and impact wear behaviors of pangolin scales from different hydrated levels were investigated on a low-velocity impact wear tester. The dynamic response and damage behavior of these pangolin scales were systematically analyzed. Results showed that the energy absorption and impact contact force were considerably distinct with different hydrated levels. The maximum values of the impact contact force are similar to each other in various impact cycles. However, the damage extent of scales was not the same in varied impact cycles. Impact worn scars size of scales increased as the impact cycles increased. Under varied hydrated levels, energy absorption initially decreased and then increased with the increase in moisture content. Specifically, for a hydrated level of 10.5%, the energy absorption had the lowest rate, down to 26.6%, and the impact force decreased. Finally, the mechanisms and factors affecting the dynamic response and impact wear of scales were investigated. This study promoted a bio-inspired design for improving impact wear resistance properties. [ABSTRACT FROM AUTHOR]

The fatigue crack growth rate (FCGR) of ER8C high‐speed railway wheel rim material was tested at various service temperatures. The temperature sensitivity of fatigue crack propagation was evaluated, and the effect of temperature on the crack propagation mechanism was analyzed. The obtained results indicate a fatigue ductile‐to‐brittle transition (FDBT) point at −20°C for the ER8C wheel rim materials. A reverse relationship was found between FCGR and temperature for the near threshold and Paris regimes when the temperature was below the FDBT point. However, no evident changing rule was found when the temperature was above this transition point. An evident fatigue crack propagation mode transition was found from lamellar tearing to intergranular cracks, which was related to the FDBT for the near‐threshold regime. [ABSTRACT FROM AUTHOR]

The impact wear behavior of Ti-6Al-4V alloy treated with laser shock peening (LSP) and without treatment were investigated under sand environment using an independently developed impact wear tester. The dynamic response, interface response, and wear mechanism under different impact kinetic energies and during wear evolution were analyzed. ANOVA analysis results show that LSP has no significant effect on mechanical properties and wear resistance of Ti-6Al-4V alloys under the same test conditions. When the impact kinetic energy was relatively low or number of the impact cycles was relatively small, the worn surface was significantly higher than the original surface. When the impact kinetic energy was relatively high or the number of impact cycles was relatively large, the center of wear scars was a pit, and the edge of wear scars was higher than the original surface. Experimental results also showed that the absorbed energy was closely related to the wear of the material during the impact-abrasive wear. The greater the loss of material was, the more energy was absorbed. The impact wear mechanism under the sand condition was mainly plowing, micro-cutting, extrusion spalling, and press-in particle on the surface of the specimens. • The impact-abrasive wear behavior of LSP Ti-6Al-4V alloys was analyzed. • The effects of the impact energy and cycles on the wear behavior were analyzed. • The dynamic response, interface response, and wear mechanism were investigated. [ABSTRACT FROM AUTHOR]

Micro-arc oxidation (MAO) coating with different oxidation times was prepared on aluminum alloy to improve the impact wear resistance of aluminum alloy. Surface morphology and impact wear behavior of the coating with different oxidation times were investigated. Results showed that the MAO coating formed on aluminum alloy had a porous and island structure comprising α-Al 2 O 3 and γ-Al 2 O 3. Coating thickness increased with increasing oxidation time. The coating also had a lower impact force and higher energy absorption ratio than the substrate but had a lower wear volume, which decreased with increasing oxidation time. These results indicated that MAO coating can improve the impact wear resistance of aluminum alloy. Further study revealed that the wear mechanism of aluminum alloy was oxidation wear and contact fatigue spalling, whereas that of MAO coating was contact fatigue wear. • The characterization and impact wear behavior of the MAO coating with different oxidation times was investigated. • The wear mechanism of aluminum alloy and MAO coating was discussed. [ABSTRACT FROM AUTHOR]

Abstract The beetle has evolved over several hundred million years and possess perfect structure, as well as performance. According to the excellent structure and performance of beetle forewing, a bionic structural material (BSM) was designed and manufactured to improve its low-velocity impact resistance behavior. The surface layer of BSM is carbon-fiber-reinforced plastic (CFRP), and the cores of BSM are aluminum honeycomb. This study aims to investigate the dynamic response, energy absorption, and damage characteristics of BSM in low-velocity and high-cycle impact condition. Results showed that the BSM is superior to single CFRP, with lower peak force, higher energy absorption, and deformation. The damage mechanism of CFRP under cycling low kinetic energy is delamination and then fracture. Meanwhile, the damage of CFRP in sandwich structures is lower than in single CFRP, indicating an excellent impact resistance behavior of BSM, which is useful for practical engineering applications. Graphical abstract The structure of the beetle forewing and impact resistance composite design.(a) Adult beetle. (b) Outline sketch of the forewing (c) surface and (d-h) cross-section and a simple model and microstructure of beetle forewing (i). Image 1 [ABSTRACT FROM AUTHOR]

Abstract 304 stainless steel (SS) was exposed to 325 °C water condition to simulate the operation condition of nuclear power reactor. The microstructural characteristics and corrosion behaviors of exposed 304 SS was investigated. Result shows that the exposed 304 SS surface form an oxide film, which consist of outer film and inner film. The outer film is composed of μm-size hematite and nm-size spinel oxide particles formed on top of the original metal surface. The continuous inner film contains Nano-crystalline spinel. Potentiodynamic polarization test results indicate that the corrosion behavior of 304 SS decrease with exposure time increasing. Because the quantity of pores on oxide film increase with exposure time increasing, and the corrosion behavior decrease. The oxide film gradually grows with exposure time. Finally, the formation and evolution mechanism of oxide film was proposed and the determining factors was discussed. Highlights • 304 stainless steel was exposed to 325 °C water condition to simulate the operation condition of nuclear power reactor. • The characterization and corrosion behaviors of the oxide film formed on 304 stainless steel surface was investigated. • The formation mechanism of the oxide film formed on 304 stainless steel surface was discussed. [ABSTRACT FROM AUTHOR]

F6NM martensitic stainless steel was exposed to 350 °C water condition for 500, 1500, and 2500 h to simulate pressurized water reactor (PWR) condition. The characterization and corrosion behavior of the oxide film were investigated. Results indicate that the exposed steel surface formed a double-layer oxide film. The outer oxide film is Fe-rich and contains two type oxide particles. However, the inner oxide film is Cr-rich, and two oxide films, whose thicknesses increase with increasing exposure time. The oxide film reduces the corrosion behavior because the outer oxide film has many crack and pores. Finally, the mechanism and factors affecting the formation of the oxide film were investigated. [ABSTRACT FROM AUTHOR]

The effect of an initial pre-compressive stress load on the low-velocity impact wear behavior of Inconel 690 alloy tubes was investigated. Interface dynamic response and damage behavior were evaluated under varied pre-stress loads. With the increase in pre-stress, tube deflection decreased, whereas the contact peak force and wear scar areas increased. Moreover, the energy absorption ratio gradually decreased and finally reached equilibrium. Analysis of the wear scars revealed that both iron and oxygen contents increased in the wear region. Furthermore, numerous surface delamination were observed in the impact area. Thus, fatigue spalling and oxidation are the wear mechanisms of the impact-fretting wear of Inconel 690 alloy tubes. [ABSTRACT FROM AUTHOR]

In this study, low velocity impact tests were performed to MoS 2 /Pb nanocomposite coating and its substrate (304-stainless steel, for comparison). The machine is controlled based on kinetic energy and can achieve dynamic response during the tests. The MoS 2 /Pb coating exhibits better impact wear resistance, as shown by its favorable dynamic response. The energy absorption ratio evolution of MoS 2 /Pb coating indicates there were several impact damage forms during the tests, which was relevant to varied dominant impact damage mechanisms. In addition, tests with varied impact conditions were conducted, and distinct results were obtained, revealing the effects of tests parameters. Moreover, comparative analysis between values obtained from the Hertz theory and the measured revealed that the yield strength of MoS 2 /Pb coating was approximately 686.5 MPa, and the substrate was always under elastoplastic deformation although its impact kinetic energy was the lowest. The low velocity impact morphology was characterized by fatigue delamination because of the shearing stress in the subsurface. [ABSTRACT FROM AUTHOR]

This study investigated the effects of electrical contact resistance (ECR) on pogo pins used in mobile phones, chargers, digital cameras, Bluetooth headsets, medical equipment, and other electronic products with different surface roughness. Experimental results revealed that metallic wear debris is generated by fretting motion and formation of a third body on rough surfaces without removal by fretting motion, thus increasing ECR. Wear debris does not easily form the third body at contact areas of smooth surfaces and causes formation of metal–metal contact pattern. Results showed low ECR with fretting motion. 3D and 2D profiles of contact area verified the definition of contacting high spots, further explaining increases in ECR. [ABSTRACT FROM AUTHOR]

The impact fretting wear behavior of a 690 alloy tube affected by low-impact cycling kinetic energy was investigated. The Inconel 690 alloy specimen was clamped by cantilever and simple supported beam structures for support. The interface response was affected by the clamping situation, and material wear was affected by the change in the interface response. The energy loss, contact force versus time and frequency, energy absorption, and deformation of the material (thin wall tube) during impact were analyzed. The worn surfaces and cross-sectional morphologies were observed with an optical microscope and a 2D surface profiler to analyze the impact fretting wear mechanism under the two support structures. In the two clamping structures, wear decreased when the span increased, and material wear showed a high correlation with the peak impact force and absorbed energy. The wear mechanism of the alloy 690 specimen was delamination. [ABSTRACT FROM AUTHOR]

The elevated temperature can cause serious failure of electrical contact. The fretting wear behavior of two typical materials (aluminum and silver) and contacts at elevated temperatures (from RT to 300 °C) and normal loads (10 N) is addressed in this paper. The morphology and wear surface was analyses by 3D profile and SEM. The results show that elevated temperature significantly affected the contact resistance. Easily oxidized metal usually have higher ECR value under elevated temperature. Elevated temperature accelerated the formation of oxide film and lead to debris which oxidizes, forming an insulating layer. Metal with good ductility and resistant to oxidation shows lower ECR. [ABSTRACT FROM AUTHOR]

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]

Tribological properties of graphene nanosheets (GNS) as lubricating oil additives on textured surfaces were investigated using a UMT-2 tribotester. The lubricating fluids keeping a constant temperature of 100 °C were applied to a GCr15 steel ball and an RTCr2 alloy cast iron plate with various texture designs (original surface, dimple density of 22.1%, 19.6% and 44.2%). The oil with GNS adding showed good tribological properties (wear reduced 50%), especially on the textured surfaces (the reduction in wear was high at over 90%). A combined effect between GNS additives and laser surface texturing (LST) was revealed, which is not a simple superposition of the two factors mentioned. A mechanism is proposed to explain for these results −the graphene layers sheared at the sliding contact interfaces, and form a protective film, which is closely related with the GNS structures and surface texture patterns. [ABSTRACT FROM AUTHOR]

A ball-on-plate wear test was employed to investigate the effectiveness of graphene (GP) nanoparticles dispersed in a synthetic-oil-based lubricant in reducing wear. The effect by area ratio of elliptically shaped dimple textures and elevated temperatures were also explored. Pure PAO4 based oil and a mixture of this oil with 0.01 wt% GP were compared as lubricants. At pit area ratio of 5%, GP-base oil effectively reduced friction and wear, especially at 60 and 100°C. Under pure PAO4 oil lubrication, the untextured surfaces gained low friction coefficients (COFs) and wear rates under 60 and 100°C. With increasing laser—texture area ratio, the COF and wear rate decreased at 25 and 150°C but increased at 60 and 100°C. Under the GP-based oil lubrication, the textured surface with 5% area ratio achieved the lowest COF among those of the area ratios tested at all test temperatures. Meanwhile, the textured surface with 20% area ratio obtained the highest COF among those of the area ratios. With the joint action of GP and texture, the textured surface with 10% area ratio exhibited the best anti-wear performance among all of the textured surfaces at all test temperatures. [ABSTRACT FROM AUTHOR]

Dual-rotary fretting (DRF) is a complex fretting wear mode combining torsional fretting with rotational fretting. Two different typical friction-induced convex topographies (Type I and Type II) in contact area were showed, which are under the control of torsional and rotational fretting components, respectively. To investigate their evolution characteristics and formation mechanism, the convex topographies were analyzed by SEM, XPS, a nano-hardness tester and surface profilometry, etc. The results show that the convex topographies significantly depended on the test parameters and environmental conditions. The initiation and propagation of fretting fatigue cracks were found related with the convex topography under the fretting wear. [ABSTRACT FROM AUTHOR]

Tribological tests were conducted on an AISI A2 steel plate against an AISI 51200 steel ball lubricated by SAE 0W30 and PAO 4 cSt base oils containing no additive package. Friction and wear behaviors were evaluated at room temperature (RT, 23 °C) and a series of elevated temperatures (75, 100, 125 and 175 °C). The steady-state friction coefficient appeared to be proportional to the oil temperature, probably because reduced oil viscosity at a higher temperature caused more surface asperity collisions. In contrast, wear results did not follow the trend: the wear rate surprisingly decreased when the oil temperature increased from RT to 75−100 °C, and then turned around to increase along with the temperature at above 100 °C. Evidentially, there are other significant factors than just the oil viscosity that influence the wear process upon the temperature change. Wear scar morphology examination and surface chemical analysis revealed an oxide-containing surface film on the wear scars and higher oxide content and larger film coverage seemed to reduce the wear rate. Therefore, the wear mechanism is proposed as a combined effect of mechanical material removal and protective surface film formation: the former largely depending on oil viscosity that is inversely proportional to the temperature and the latter involving surface and wear debris oxidation that is promoted by temperature elevation as well as the water content (up to 100 °C) in the oil. [ABSTRACT FROM AUTHOR]

Tribological evaluations were conducted on lubricating base oils of different viscosity grades with and without an anti-wear (AW) additive in lubricating steel-steel and ceramic-steel contacts. Two AW additives were applied: a conventional secondary zinc dialkyldithiophosphate (ZDDP) and an oil-miscible phosphonium-phosphate ionic liquid (IL). Tests were carried out using reciprocating ball-on-flat sliding at room temperature. The flat material was AISI A2 tool steel, and the ball material was either AISI 52100 bearing steel or silicon nitride. Four lubricants were tested: Chevron SAE 15W40 and 0W30 base oils, and the 0W30 base oil plus 1 wt% ZDDP or IL. For the steel–steel contact, the lower-viscosity 0W30 base oil resulted in a higher wear rate than did the 15W40 base oil, as expected. Both the ZDDP and the IL substantially reduced wear, and the IL-additized 0W30 base oil was the best performer. For the ceramic–steel contact, the ZDDP provided moderate wear protection for both ball and flat. In contrast, the IL reduced the steel flat wear more effectively but increased the ceramic ball wear rate. Cross-sectional transmission electron microscopy (TEM) examination and x-ray photoelectron spectroscopy (XPS) chemical analysis were used to reveal the thickness, nanostructure, and composition of the tribofilms formed by ZDDP and IL on the steel and silicon nitride surfaces. [ABSTRACT FROM AUTHOR]

The fretting corrosion behavior of quench–polish–quench (QPQ)-treated TP316H steel was investigated in liquid sodium at 450 °C. The surface of the sample after QPQ is a multi-layer structure, consisting of the outermost oxide layer, the middle nitriding layer, and an underneath diffusion layer. The fretting wear and corrosion increased the material damage. With increasing thickness of the nitriding layer, the cross-sectional hardness and wear resistance remarkably increased, the fretting corrosion volume decreased. The effect of multilayer structure anti-wear and anti-corrosion were examined. Possible fretting corrosion mechanisms of the multilayer structure prepared by QPQ on TP316H in liquid sodium are discussed. • Time of QPQ treatments influence the multilayer structure of modified surface. • The high-hardness nitriding layer exerts the main anti-wear effect. • The diffusion layer exerts better anti-corrosion effect, and decomposes into the harder CrN and α-Fe phases. • QPQ treatments are promising for combating fretting corrosion of TP316H in liquid sodium. [ABSTRACT FROM AUTHOR]

The fretting corrosion behavior of zirconium (Zr) alloy under different pH conditions was investigated. The morphology, microstructure, and wear mechanism of Zr alloy under different pH condition was analyzed. The results indicate that the wear scar Zr alloy in acid condition presents a typical feature of wear debris, furrow, and delamination, indicating that the wear mechanism is oxidation wear and abrasive wear. The microstructure beneath the wear scar is composed of a thick wear debris layer (WDL), deformation layer (DL), and thin tribologically transformed structure (TTS). The WDL is a nano-sized grainy structure and the micro-crack is mainly formed on the interface of WDL and TTS. The largest wear volume belongs to the wear scar in pH of 1 condition. Because the corrosion and corrosion induced by wear would destroy the surface protective film and form a thick WDL, which is easy to separate to increase the material loss volume. The Zr alloy in pH of 1 condition shows the largest volume ratio of wear induced by corrosion and corrosion induced by wear. • The material loss volume by tribocorrosion is lowest at intermediate pH and highest at low pH. • The thick WDL at low pH is generated by the quick oxidation of TTS/DL and the accumulation of oxide particles. • The wear mechanism of Zr alloy at intermediate pH is abrasive wear and at low pH is oxidation wear and abrasive wear. [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: Fretting displacements of a shrink-fitted PMMA shaft subjected to rotating bending by a newly produced bending fretting device are observed and measured in situ, which are also analyzed by numerical simulations. The results show that the fretting mode of the shrink-fitted shaft is a kind of composite tangential fretting combining both axial and transverse motions and the relative sliding trajectory is approximately in a spindle shape. Besides, the fretting could be transitional between the partial slip and gross slip and the sliding velocity is also continuously varied. [Copyright &y& Elsevier]

Under different simulated oral environments (distilled water, artificial saliva, and a cola soft drink) and with a small-amplitude reciprocating apparatus, the friction and wear behaviors of 5 types of indirect dental restorative composites relative to uniform SiN balls were investigated. Test parameters were: normal load with 20 N, reciprocating amplitude (1,000 μm), and frequency (0.25 Hz). Tests lasting up to 5,000 cycles were conducted. The wear damage characteristics are discussed in detail based on an analysis of friction behaviors, SEM observations, and 2- and 3-D profile microscopy. The results indicated that the hybrid resin composites with high filler weight and well filler distributions, such as Filtek P60, possess better wear resistance than nano-filled composites, such as VITA ZETA and VITA LC, with relatively low filler weight. Artificial saliva and a cola soft drink could play important roles in lowering the friction coefficient and wear loss of dental composites. The cola soft drink displayed a better lubrication effect. The degree of sensitivity to changes in lubrication conditions varies with different dental composites. Abrasive wear is the main wear mechanism for the 5 composites, but brittle cracks and delamination are more common for VITA ZETA and VITA LC. [ABSTRACT FROM AUTHOR]

Abstract: Radial fretting tests on human femur cortical bone with a ball-on-flat configuration were carried out in vitro under different normal contact loads. The kinetics behaviors and damage characteristics of the cortical bone were analyzed using the load versus displacement (F–D) curves. The fretting scars were examined using laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM). A nano-indenter was used to characterize the mechanical property of the osteon of the cortical bone. Morphologies showed that the primary damage form was due to micro-cracking. Around the osteon, three kinds of micro-crack configurations were observed; i.e. annular cracks—located at the concentric lamellae; radial cracks—initiated from the Harversion canal; and interstitial cracks—initiated and propagated between the interstitial lamellae. Plenty of interstitial cracks occurred in the wear scar, which indicated that the interstitial tissue was the weak zone in the structure of cortical bone. In addition, the contact stresses under the radial fretting condition were calculated by the finite element method analysis (FEMs) and the behaviors of cracking were explained. The results demonstrated that the stress concentration that occurred around the Harversian canal and osteon system resulted in a better resistance than that from the interstitial tissue. The concentric lamellae presented a better radial-fretting resistance and contact fatigue resistance than that from the interstitial lamellae. [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]

The high‐temperature fretting fatigue damage characteristics of dovetail specimens strengthened by nanosecond laser (NL) and nanosecond combined femtosecond laser (F‐NL) were investigated. The results show that the fretting fatigue life of the NL strengthened sample (NL sample) is improved by 211.2% compared to the base metal samples (BM sample). The lifetime of the nanosecond combined femtosecond strengthened sample (F‐NL sample) was increased by 319.6%. It was attributed to the strengthening introducing hardened layers, residual compressive stress field, and high density of dislocations. The combined strengthening process reduces the surface roughness of the NL strengthened surfaces, while the strengthening influence layer is further increased. The fracture morphology shows that the crack source of the strengthened specimen has changed from multi‐source sprouting to single‐source sprouting, and the crack source sprouted on the subsurface. The fatigue strip morphology similarly confirms that a reduction in the crack propagation rate occurs. [ABSTRACT FROM AUTHOR]

The micro-arc oxidation (MAO) coating with different nanoparticles (Al 2 O 3 , MoS 2 , CeO 2 , and graphene oxide (GO)) was prepared on zirconium (Zr) alloy. The surface morphology, cross-section morphology, element composition, and phase structure of different composite MAO coating were investigated. Results show the composite MAO coating consists of ZrO 2 and nanoparticle, along with all the coating present a typical porous structure. The composite MAO coating is comprised of an outer porous layer and inner dense layer, and most of the nanoparticle is gathered to the outer layer. The electrochemical results demonstrate that composite MAO coating presents better corrosion protection to Zr alloy, and the MAO coating with Al 2 O 3 shows the best corrosion resistance. Because the Al 2 O 3 nanoparticle can stabilize the t-ZrO 2 during MAO process and has a denser inner layer. Meanwhile, the nanoparticles in the coating can play the part of a barrier to the diffusion pathway of corrosion medium and restrain aggressive corrosion medium entering the Zr alloy. The fretting corrosion test shows that the MAO coating with GO has the lowest wear volume, and it has the highest material loss volume ratio of corrosion induced by wear. Because GO in MAO coating can reduce the friction by small shear force between the layers. • The formation mechanism of MAO coating with different nanoparticles was proposed. • Role of nanoparticles on the corrosion behavior of MAO coating was inveatigeted. • MAO coating with GO shows the highest material loss ratio of corrosion induced by wear. [ABSTRACT FROM AUTHOR]

• 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]

Various impact-sliding wear behaviors commonly occur among steam generator tubes and their supporters. The main purpose of this study is to investigate the effect of ultrasonic surface rolling process (USRP) on the impact-sliding wear behavior of Inconel 690 alloy tubes. A self-made two-dimensional cycling impact-sliding wear test rig was developed to realize multiple wear patterns by changing motion parameters in both impact and sliding directions. Tests were carried out under different impact and sliding velocities. Results indicated that USRP reduced the impact kinetic energy absorption rate, friction coefficient and increased the wear resistance of Inconel 690 alloy. These can be attributed to the USRP which decreased the grain size of 690 alloy, resulting in the increase of micro-hardness and compressive residual stress. Image 1 • USRP is capable to refine microstructure, improve micro-hardness and compressive residual stresses of 690 alloy tubes. • USRP treated samples showed better wear resistance and lower friction coefficient under impact-wear sliding condition. [ABSTRACT FROM AUTHOR]

Nuclear power plants, working in extremely harsh environment, primarily in the form of high-speed fluid flow, circulate through complex systems. Serious tribological problems can occur when a small amount of nuclear energy is converted into mechanical energy in the components (e.g., fuel-rod cladding, tube of the heat exchange systems). With the increase of the service life of nuclear power equipment, a considerable number of nuclear power equipment or structure failures occur one after another. Although the influencing factors are different, fretting damage is one of the important factors. Fretting damage has strong concealment and high risk, and it is often the main cause of component failure. Thus, improving the reliability of nuclear power equipment, extending their life, and optimizing their structure are important. In recent decades, many scholars have studied fretting wear, fretting fatigue, and fretting corrosion behavior in nuclear power equipment. Accordingly, they have solved many problems, accumulated a lot of experience, and put forward many criteria. In this article, the research status of fretting damage in key equipment and structures of nuclear power plant is reviewed. Typical positions of fretting wear in steam generator. Image 1 • The research status of fretting method, nuclear materials damage in key equipment and structures of nuclear power plant is reviewed. • Fretting research of heat exchange materials for steam generators and fuel cladding in nuclear power systems is reviewed. • The research status of fretting wear of fuel cladding is analyzed, including the latest coating and surface strengthening technologies. [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]

Wear behaviors of materials in nuclear power stations are very complex, because they are rarely subject to just pure impact or sliding wear. This study uses a self-made impact-sliding wear test rig to study the influences of impact kinetic energy and sliding velocity on the energy absorption, mechanical response, interface deformation, and damage behavior of nuclear-grade 304 stainless steels (304SS). The results show that an increase in impact velocity causes an increase in absorbed energy, impact force, and friction force, while lowing the friction coefficient. The friction force and friction coefficient increase with an increase in the sliding velocity, whereas no obvious change is seen in impact force and absorbed energy. The dominant wear mechanism in test samples were delamination failure and friction oxidation. Furthermore, numerical study was performed to explain the effect of velocity on the mechanical response of 304SS. • The impact-sliding wear test rig is capable of testing the wear behaviors of different materials under various complex conditions. • Effect of different impact kinetic energies and sliding velocities on the impact-sliding wear behaviors of nuclear material was studied. • Effect of impact kinetic energies on the dynamic response of impact-sliding wear is more obvious than that of the sliding velocities. [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]

Cam mechanism is widely applied in industry because it can help achieve various complex motions of the follower via the cam contour design. However, its performance is significantly affected by the wear condition. This study proposes a load distribution measurement instrument to assist the study on friction and wear regularities of oscillating follower cam mechanisms through obtaining the normal pressure (F) and friction force (Ff) distributions along the cam profile. In the instrument, F and Ff are automatically calculated via a MATLAB program based on the geometry and the measured rotary resistance torque and rotary angle of the cam. The latter two parameters are obtained through a static torque sensor and a rotary encoder built in servo motor in real time, respectively. An experimental test was conducted and the cam morphology after service was observed using scanning electron microscopy. Results show that the wear condition of the cam is significantly related to the corresponding F and Ff. Complex load parameters of oscillating follower cam mechanisms can be provided by this instrument, which is crucial in understanding the friction and wear behaviors of cams and finding the vulnerable position. [ABSTRACT FROM AUTHOR]

To investigate the wear mechanism and microstructural evolution of Ti6Al4V titanium alloy under the condition of dual rotary fretting (DRF), which mainly exists in the interfaces of ball-and-socket joints with the motion combing torsional fretting with rotational fretting. Using the Ti6Al4V titanium alloy flat specimen against the 52100 steel ball to investigate the DRF and damage behavior were carried out under the normal load of 50 N with different tilt angles (10°~60°) and varying angular displacement amplitudes (0.25°~5°). The morphologies of wear surface and their cross-sections were analyzed by scanning electron microscopy, electron probe microscopy analyzer and a surface profilometer etc. The results are as followed: 1) The DRF wear behavior of Ti6Al4V is strongly dependent on the tilt angle, which decides the scale for combination of rotation component and torsion component. 2) F x /F n curves presents different varied trends in different fretting regimes. The fretting wear is slight in partial slip regime due to the oxidative wear, and the surface bulge is formed in mixed fretting regime probably due to the plastic-flow, and in sliding regime, plough scratches caused by the abrasive wear. 3) As the tilt angle increase, DRF wear mechanism of Ti6Al4V titanium alloy transfers from oxidative wear to the abrasive wear. 4) The DRF damage of Ti6Al4V is the result of the competition between the rotational fretting component and the torsional fretting component. When the DRF behavior is mainly controlled by the torsional fretting component, the wear mechanism is the oxidative wear with the oxygen element distributing around the micro-slip circle zone. When the DRF behavior is mainly controlled by the rotational fretting component, the severe plastic deformation can be observed. [ABSTRACT FROM AUTHOR]

In the pressurized water reactor nuclear power plant, 316L SS chips were captured by the support grid and continued to affect the Zr-4 cladding tube, causing the fuel rods to wear and perforate. In this work, a 60° acute angle cone of 316L SS was used to simulate the cyclic impact of debris on a Zr-4 alloy tube with different initial impact velocities and impact angles. Results showed that increasing the initial impact velocity will generate a wear debris accumulation layer with a wear-reducing effect, but also promote the extension and expansion of fatigue cracks, resulting in the delamination of Zr-4 alloy tubes. The inclination of the impact angle increases the energy loss. The energy loss rate of the 45° impact is as high as 69.68%, of which 78% is generated by the impact-sliding stage. The normal force is mainly responsible for the wear removal and plastic deformation of Zr-4 alloy tubes. Tangential forces cause severe cutting in Zr-4 alloys and pushes the resulting wear debris away from the contact surfaces. [ABSTRACT FROM AUTHOR]

Lubricant anti-wear additives are known to chemically interact with metallic surfaces to form a self-healing, wear-protection tribofilm. Their interactions with non-metallic surfaces are however less understood. Here we report recent findings on whether and how a zinc dialkyldithiophosphate (ZDDP) and a phosphonium–organophosphate ionic liquid (IL) form tribofilms on three hard coatings, AlMgB 14 –TiB 2 , TiB 2 , and diamond like carbon (a-C:H DLC), when sliding against a steel ball. Systematic characterization was conducted on the coating wear scars including top surface morphology imaging and elemental mapping, layer-by-layer chemical analysis, and cross section nanostructural examination. The ZDDP and IL tribofilms on the boride coatings are up to 50–70 nm thick with 75–80% surface coverage while the tribofilms on DLC were <25 nm thick and only covered 20–30% of the contact area. The presence of iron compounds in the tribofilms suggests a critical role for wear debris in tribofilm formation. Oxidation products of TiB 2 were detected in the tribofilms, while no involvement of the DLC surface in tribofilm formation was observed. Results suggest that wear debris digestion and contact surface reaction both are critical in tribofilm formation: the former process is responsible in forming the bulk of the tribofilm and the latter provides strong bonding of the tribofilm to the contact surface. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this study is to investigate the lubrication of hyaluronic acid (HA) and chondroitin sulfate (CS) on the condylar cartilage of the temporomandibular joint. The wear behaviour of bovine condyle cartilage was explored against a zirconia ball with different lubrications under torsional fretting mode. The worn cartilage morphologies were observed using scanning electron microscopy and hemotoxylin and eosin staining. The results indicated that HA or CS could significantly lower the friction torque and dissipated energy of fretting interface and reduce the damage of the articular cartilage surface compared to the control (phosphate-buffered saline). The mixture (HA and CS) could provide better protection for the cartilage layer. Absence of good lubrication in overloading torsional fretting process caused excessive cartilage wear. High concentration and high molecular weight HA or CS acted as good boundary lubricants, and the lubrication effect of their mixture was better due to their synergistic function. Copyright © 2014 John Wiley & Sons, Ltd. [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]

• Microstructure and fretting wear properties of Zr alloys treated by LSP were studied. • The plastic deformation was caused by grain refinement and dislocation entanglement. • Zr alloys treated by LSP exhibit abrasive wear and oxidation wear. In this study, the microstructure and fretting wear properties of zirconium (Zr) alloy treated by laser shock peening (LSP) were studied. The Zr alloy treated by LSP presents grain refinement and dislocation entanglement, resulting in the increase of hardness. The friction coefficient, wear area, wear loss, and wear depth of Zr alloy treated by LSP are significantly reduced, indicating that LSP treatment can enhance the wear resistance. The primary wear mechanism of substrate is adhesive wear, and Zr alloy treated by LSP exhibits abrasive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

In this work, the contact force model and experiment methods were used to study the dynamic response and impact wear behavior of TP316H steel. The Flore model and the classic Hertz model were selected for comparison with the experimental results, and the model was revised according to the section parameters of the TP316H tube. The results show that there is a large difference between the models without considering the effect of structural stiffness on the impact system and the test results, whereas the revised model has a good agreement. With the rise in impact mass, the coefficient of restitution increases from 0.65 to 0.78, whereas the energy dissipation and wear volume decrease. Spalling, delamination, plastic deformation, and oxidative wear are the main impact wear mechanism of TP316H steel. [ABSTRACT FROM AUTHOR]

• Annealing at different temperatures was used on cold rolling fe-13cr-4al-2mo thin-walled tubes. • The microstructure and axial tensile properties of the samples before and after annealing were measured. • The annealed samples were embrittled by aging, and the enhanced particles and hardness were characterized. • The strengthening mechanism of FeCrAl alloy at room temperature and failure mechanism at high temperature were investigated. FeCrAl alloy has great application potential to replace traditional zirconium alloy as an accident-tolerant fuel (ATF) candidate material. In this study, Fe-13Cr-4Al-2Mo-0.65Nb-0.4Ta alloy was prepared into a thin-walled tube with a diameter of 9.5 mm and a wall thickness of 0.35 mm by cold rolling. The effects of different annealing temperatures on the microstructure morphology, texture growth direction, and mechanical properties of FeCrAl alloy were studied., alloy underwent recovery and recrystallization with increasing annealing temperature, and the grain size increased. The theoretical calculation showed that the pinning action of Fe2Mo4C and Fe2Nb increased the dislocation density, and the interaction with the dislocation increased the room temperature strength. The addition of Ta led to the formation of more second-phase precipitates at the grain boundary, which hindered the growth and refined grains. The high-temperature stable second phase provided sufficient temperature strength for the alloy. [ABSTRACT FROM AUTHOR]

Abstract: Bending fretting fatigue tests of 7075 aluminum alloy cylinders against 52100 steel cylinders orthogonally have been carried out under a same normal load and varied bending loads. The S–N curve of the bending fretting fatigue showed a characteristic of “C curve”. Based on the OM, SEM, and TEM, the fretting fatigue damages of 7075 alloy have been analyzed in detail. A physical model was set up to describe the surface damage and the crack formation process in MFR. The TEM analyses showed that the stress concentration at the wall of dislocation cells was the reason of the fatigue crack initiation. [Copyright &y& Elsevier]

• Surface morphology changes in the DD6 and TBC with various laser powers are studied. • The mechanism of fs laser on the DD6 and TBC is phase explosion and vaporization. • Laser spot regions includes ablation, melting, laser-induced, and irradiated regions. In recent years, single-crystal superalloy and thermal barrier coating (TBC) have attracted considerable attentions in femtosecond laser drilling. Surface morphology changes in DD6 single-crystal superalloy and TBC induced by incident laser pulses with a wide range of powers (2.28–11.18 W) at 50 kHz are studied. The ablation thresholds of DD6 single-crystal superalloy and TBC are calculated, and the ablation mechanisms of different femtosecond laser spot regions are discussed in details. Results show that the ablation threshold of DD6 single-crystal superalloy is 1.16 J/cm2, which is close to that of TBC (0.998 J/cm2). The femtosecond laser spot regions in the DD6 single-crystal superalloy and TBC can be divided into four (ablation, melting, laser-induced, and irradiated regions) on the basis of the energy distribution of the Gaussian laser beam. However, the physics behind femtosecond laser on single-crystal superalloy is laser-induced periodic surface structures (LIPSS), where is laser-induced cracks (LIC) on TBC. The dominant mechanism differs in different regions. The reason for cracks on the TBC may be the combined action of thermal stress and mechanism stress under high fluence and high repetition rate femtosecond laser. [ABSTRACT FROM AUTHOR]

The tribologically transformed structure of the white etching layer (WEL) always appears with some cracks accompanying microstructural evolution under friction. This work investigated crack behavior with the existence of WEL on pearlitic steel after rolling-sliding friction tests. The WEL microstructure was characterized using scanning electron microscopy, nano-indentation, focused ion beam, and transmission electron microscopy. According optical images, the WEL zone could be divided into white and yellowish zones; cracks existed at the boundary separating these two zones. The deformation degree of the cementite structure caused color differences in optical images and inhomogeneous chemical composition distributions in the same WEL zone. For cracks initiated and propagated at the WEL colony boundary, crack holes remained unconnected along the plastic deformation line. • Crack initiation and propagation in white etching layer (WEL) are investigated. • Under rolling–sliding friction, WEL of cementite appears on pearlitic steel. • WEL contains two "phases" of dissolved versus nanoscale cementite. • Cementite form determines color of WEL under optical microscopy. [ABSTRACT FROM AUTHOR]

Ultrasonic surface rolling processing (USRP) was carried out at zirconium (Zr) alloy with different rolling speeds to prepare gradient nanostructured layers, and the corrosion behavior of USRP treated Zr alloy was studied under 360 °C/18.6 MPa water condition. The surface morphology, microstructure, phase composition, and element distribution of USRP treated Zr alloy after corrosion was investigated. Results show that the oxide layer on Zr alloy comprises of t-ZrO 2 , m-ZrO 2 , and metal Zr. The thickness of oxide layer Zr alloy is reduced after USRP treatment, indicating that the gradient nanostructure can effectively improve corrosion resistance. This process is attributed to that the gradient nanostructure layer is helpful for the nucleation of equiaxed t-ZrO 2 at the oxide/metal (O/M) interface with small grain size. The high compressive stress induced by USRP treatment is beneficial for the maintenance of t-ZrO 2 phase and inhabiting the phase transformation from t-ZrO 2 to m-ZrO 2 , which reduces the micro-cracks and defects due to volume expansion. The oxide layer on USRP treated Zr alloy with high content of t-ZrO 2 phase presents a dense structure and prevents oxygen anions from diffusing to Zr alloy. • The characterization of oxide layer on USRP treated Zr alloy is investigated. • The gradient nanostructured layer is beneficial for improving the corrosion behavior of Zr alloy. • The corrosion mechanism of USRP treated Zr alloy is analyzed. [ABSTRACT FROM AUTHOR]

Low energy laser shock peening (LE-LSP) with different energies was carried out at zirconium (Zr) alloy. Characterization and electrochemical corrosion behavior of Zr alloy after LE-LSP treatment were investigated. Results show that the surface profile of Zr alloy after LE-LSP treatment is rough due to the regular undulations on the surfaces. The hardness of Zr alloy increases after LE-LSP treatment because the grain size of Zr alloy is refined, and the plastic deformation generated on the surface induces the working hardening. A melting layer, plastic deformation layer, and transition layer are formed on Zr alloy after LE-LSP treatment. The dislocation entanglement is observed at the plastic deformation layer, which indicates that the dislocation slip is the main deformation mechanism of Zr alloy. The electrochemical corrosion resistance of Zr alloy after LE-LSP treatment is improved because of an increase in the grain boundary, which improves the activity of Zr alloy and is beneficial for forming passive films. • A melting layer, plastic deformation layer, and transition layer were formed on Zr alloy after LE-LSP treatment. • The dislocation slip is the main deformation mechanism of Zr alloy during LE-LSP process. • The increase in the grain boundary of Zr alloy after LE-LSP treatment is beneficial for forming passive films. [ABSTRACT FROM AUTHOR]