45~#钢表面纳米晶层的高温磨损特性

通过增压喷丸方式使45#钢实现表面纳米化,采用MMU-5G高温材料端面磨损试验机进行45#钢纳米晶层摩擦磨损性能随温度变化的试验,利用TEM表征喷丸后表层的组织,DSC与显微硬度研究纳米层的热稳定性,XPS和SEM表征磨损表面的成分及形貌.结果发现:当温度低于200℃时,喷丸样品表面硬度高,有效减少实际接触面积,耐磨性能优于未喷丸样品;在200～400℃之间时,纳米化样品表层组织结构中存在大量的晶界、位错、空位等缺陷为氧原子与金属原子提供更多的扩散通道,加速疏松的Fe2O3氧化物的形成与脱落,耐磨性能低于未喷丸样品;在400～550℃之间时,喷丸样品由于回复与再结晶,与未喷丸的耐磨性能基本一致.

The Sliding Wear Behavior of Nano-crystalline Surface Layer on 45# Steel at Elevated Temperature

A nanostructured surface layer was fabricated on the surface of 45# steel by high pressure shot peening. Friction and wear tests of the nanocrystalline surface layer were implemented on a Model MMU-5G high temperature friction and wear tester. Microstructure of the surface layer was characterized by transmission electron microcopy (TEM). Differential scanning calorimetry (DSC) was employed to expatiate the thermal stability of the surface layer. Composition and morphology of the worn surfaces were also characterized by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Because the high hardness of the surface layer by the strengthening of fine grains and working hardening dramatically reduced the real area of contact, the wear resistance of shot peening sample was better than that of as-received sample at temperatures ranging from room temperature to 200 oC. However, from 200 oC to 400 oC the as-received sample showed better tribological behavior that of the surface layer. It was because defects, e.g. grain boundary, dislocation, vacancy induced by the process of surface nanocrystallization were in favor of the diffusions of oxygen ions inwards and/or metal ions outwards, and hence accelerated the formation and breakdown of the loose oxide scale. Friction and wear of untreated and treated samples were comparable from 400 oC to 550 oC because of the recovery and growth of grain of the nanocrystalline layer.