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The tribological behavior of 42CrMo4/17NiCrMo6-4 under grease lubrication was explored in terms of load, speed, hardness matching, and lubrication quantity. Optical microscopy, scanning electron microscopy, and a surface profilometer were used to investigate the wear mechanism. The results show that hardness matching has the greatest impact on the wear resistance and friction reduction of the friction pair, followed by the load factor, with the impacts of speed and lubricant quantity being minor. Increasing the hardness of 42CrMo4 reduces the friction coefficient and wear volume of the friction pair substantially. When the maximum surface hardness of 42CrMo4 was compared with the lowest surface hardness, the friction coefficient was reduced by 21.5%, and the wear volume was reduced by 87.2%. Abrasive wear is the sort of wear failure that was seen, and as the hardness of 42CrMo4 increased, more severe fatigue wear appeared on 17NiCrMo6-4. While the wear volume initially increases and subsequently lowers with increasing load, the friction coefficient initially decreases and then stabilizes. A synergistic combination of abrasive and adhesive wear occurs under high load, changing the wear type from abrasive wear under low load. The wear volume is decreased by the sticky layer generated under high load conditions, which achieves superior wear prevention. This study is anticipated to offer recommendations for designing gears' required hardness under various operating circumstances. [ABSTRACT FROM AUTHOR]

With their low weights and excellent mechanical properties, TiAl alloys are expected to be applied in pistons to achieve energy savings and emissions reductions in internal combustion engines. The tribological behaviours of the Ti–48Al–2Cr–2Nb alloy against the QT600-3 material at different applied loads under oil-lubricated conditions were investigated in this study. The results showed that as the load increased, the friction coefficient and wear-scar volume significantly decreased. The wear surface of the TiAl alloy was analysed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The wear mechanism of the TiAl alloy under oil lubrication conditions was mainly the combined effect of adhesive wear and oxidation wear, different from the wear mechanism under dry-friction conditions. Furthermore, by observing the cross-sectional morphology of the TiAl alloy after focused ion beam, it was found that the QT600-3 wear debris had compacted and accumulated on the surface of the TiAl alloy, preventing further contact between the TiAl alloy and the QT600-3. This study has the potential to accelerate the application of the Ti–48Al–2Cr–2Nb alloy in lightweight pistons. • The tribological behavior between TiAl alloy and QT600-3 under oil lubrication condition is investigated. • The wear mechanism of TiAl alloy under oil lubrication condition is revealed. • The influence mechanism of the adhesive layer on tribological behavior of TiAl alloy is revealed. [ABSTRACT FROM AUTHOR]