Subsurface Dynamic Deformation and Nano-structural Evolution in 40Cr Steel Under Dry Sliding Wear

Tribological Properties of the 40Cr/GCr15 Tribo-Pair under Unidirectional Rotary and Reciprocating Dry Sliding

“…At this time, the laminar flow between pearlite and ferrite on the surface of the deformation layer was destroyed and mixed near the surface, which formed a vortex structure. Our previous study [21] reported a similar vortex structure, which was caused by uneven local stress distribution, and sub-surface observations revealed a nanocrystalline structure. Due to the local high strain [32] and shear instability [33,34] during frictional wear, the dislocation continued to accumulate with the deformation process and gradually formed sub-structures with high densities of defects, until the original gradient structure formed fragments and particle aggregates of different scales [35].…”

“…In addition, the formed structure and surrounding microstructures can be further analyzed by nanoindentation technology, which is the work we need to carry out in the future. Our previous study [21] confirmed that the vortex structure was mainly composed of nanocrystals caused by severe plastic deformation, forming hardened areas near the wear surface. As shown in Figure 6d, after 120 min of sliding, the vortex structure boundary was prone to forming cracks and peel off at the boundary.…”

“…This substructure provided enough inhomogeneity to allow shear instability, offering conditions for the creation of vortex structures [39]. The reports on the vortex structure of steel materials focused on unidirectional sliding [21,35]. Of course, this speculation requires sufficient experiments or computational analysis to verify.…”

“…At the same time, the tissue at the bottom of the vortex layer continued to transform into a vortex structure under shear (Figure 10); i.e., the vortex structure underwent a cyclic process of stripping and regrowth during steady state, during which a large number of fragmentation products were carried away from the tribo-layer. In return, an imminent stripped layer formed, and the wear rate increased [21]. The microhardnesses of different sliding modes were also compared in the report [4], but the hardnesses of different positions under reciprocating sliding was ignored.…”

“…However, the early comparative studies [16][17][18][19] of different sliding motions of steels did not take into account the microstructural evolution and microhardness gradient in tribo-layers. As one of the most widely used friction pair materials in mechanical transmission components, the tribological behaviors of 40Cr steel were mainly investigated under unidirectional sliding conditions [20,21]. There are few studies on reciprocating the tribological behavior of 40Cr steel, especially the comparison of reciprocating and unidirectional sliding friction.…”