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Abstract This study reports on fretting friction and wear behaviors of steel/copper test pairs lubricated in the nanodiamond-dispersed oil with a flat-on-flat configuration at 106 N. After 4 × 104 fretting cycles, results show that an addition of 0.2 wt% nanodiamonds in oil reduces the friction torque from 0.12 Nm of pure oil to 0.08 Nm. Particularly, the wear volume is decreased by an order of magnitude compared to that tested in pure oil. Microstructural analyses reveal that the substantial friction and wear reduction is attributed to collective effects including the formation of robust nanodiamond-strengthened tribofilms, wear-induced twin boundaries, and good mechanical bonding interface between tribofilms and the substrate. Highlights • Dispersing nanodiamonds (NDs) in oil dramatically reduced friction for fretting. • Wear volume was decreased by an order of magnitude after dispersing NDs in oil. • This can be attributed to formation of a robust nanodiamond-strengthened tribofilm. • Wear-induced TBs in the substrate also promoted to the high wear resistance. [ABSTRACT FROM AUTHOR]

The present research describes a study to explore the possibility to improve the wear resistance by healing microcracks that initiated under fretting wear. To this aim Ti 3 SiC 2 coatings prepared at different plasma powers (33 and 34 kW) were investigated comparatively under fretting. The results showed that the amount of Ti 3 SiC 2 phases was higher at the lower plasma power, leading to a major difference on fretting wear properties. Coatings with a higher content of Ti 3 SiC 2 phases exhibited a remarkable decrease in the friction coefficient and an enhancement in the wear resistance. The enhanced wear resistance was mainly attributed to the healed cracks by selective oxidation of Ti 3 SiC 2 . The reduced friction coefficient was strongly related to the formation of tribo-induced oxides. [ABSTRACT FROM AUTHOR]

Fretting wear behavior of CuNiAl against 42CrMo4 was investigated under different lubrication conditions with the flat on flat contact configuration. In oil, filtered water and artificial seawater, it was under a mixture of liquid lubrication and third body solid lubrication, so the friction torque was lower than that under dry fretting. Wear was the slightest in oil and the most serious under dry fretting. The corrosion products under seawater lubrication presented a friction and wear reducing effect. The wear mechanisms depended on the lubrications. In oil, they were dominated by abrasive wear and plastic deformation; under the two water lubrications, they were mainly cracks, delamination and abrasion; under dry fretting, they were mainly abrasive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

The surface integrity of a material has a significant impact on fretting wear performance. Based on the analysis of the material surface integrity, the machining parameters were optimized to obtain the best fretting wear performance of CuNiAl alloy. First, the effects of ultrasonic vibration-assisted milling (UVAM) processing parameters on the surface integrity of CuNiAl alloy were studied. Consequently, the relationship between UVAM processing parameters and CuNiAl alloy surface integrity parameters was established through the optimized support vector machine (PSO-SVM) model. The relationship between the surface integrity parameters, processing parameters, and fretting wear performance was established. The best fretting wear performance was obtained at a spindle speed of 147.4 m/min, feed rate of 76 mm/min, and vibration current of 199.5 mA. • The effects of ultrasonic vibration-assisted milling (UVAM) processing parameters on the fretting wear performance and the surface integrity of the CuNiAl alloy were studied. • Improvements on the surface integrity including compressive residual stress field, refined grains, higher hardness distribution and improved stress concentration coefficient are observed in UVAM-processed samples, contributing to the promotion effects on fretting wear properties. • The relationship between UVAM parameters and surface integrity parameters was established. And the surface integrity parameters were predicted by UVAM parameters. • The best wear volume was predicted by UVAM parameters and predicted surface integrity parameters. The optimized processing parameters for the best volume were obtained. The UVAM parameters optimization for the best wear volume based on surface integrity parameters was realized. [ABSTRACT FROM AUTHOR]

In this study, NiAl bronze (NAB) alloys are processed using an ultrasonic vibration-assisted milling (UVAM) surface engineering technique. The strengthening mechanisms at different cutting speeds are analysed through well-established models and experiments. The increase in cutting speed produced decrements of 29.5%, 26.6%, and 5.6% in the friction torques, accumulated dissipated energy, and worn surface area, respectively. The microhardness gradually increased by 11%, which helped improve the fretting wear performance. Grain refinement, precipitation, and dislocation strengthening were the main mechanisms. Grain refinement (∆ σ HP) had the greatest contribution to performance, followed by precipitation (∆ σ or) and dislocation (∆ σ d). Nanotwin strengthening was observed at a cutting speed of 150 m/min. Martensite nanotwins may nucleate at the grain boundary and grow toward the grain interior. [Display omitted] • The increase of cutting speed leads to beneficial effects on their fretting behavior including friction torques, accumulated dissipated energy and worn surface area for 29.5%, 26.6% and 5.6%, respectively. • The refinement of the κ phases and the effects of dislocations and stacking faults help increase the hardness and mechanisms were analysed. • The formation of martensite phases in UVAM6000 was attributed to severe plastic deformation and the special 3R martensitic structures of NAB alloys. Specifically, martensite nanotwins may nucleate at the grain boundary and then grew toward the interior of grains. • Grain refinement, precipitate, and dislocation strengthening were the main mechanisms for all samples and its contributions were calculated through well-established models and experiment data. [ABSTRACT FROM AUTHOR]