Formation of nano-laminated structures in a dry sliding wear-induced layer under different wear mechanisms of 20CrNi2Mo steel

• Published in: Applied surface science 2017-11, Vol.423, p.305-313
• Main Authors: Yin, Cun-hong, Liang, Yi-long, Jiang, Yun, Yang, Ming, Long, Shao-lei
• Format: Article
• Language: English
• Subjects: 20CrNi2Mo; Gradient structures; Plastic deformation; Wear mechanism; Wear-induced layer
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.06.187

•Dry sliding can be considered as a special severe plastic deformation technique that induces structural refinement.•For one of these the nearsurface was analysed using focused ion beam and associated TEM.•The nanostructures produced in the nearsurface layer are mainly composed of low angle boundaries.•We attributed the formation of nanolaminated structure to the presence of large strain and high strain gradient. The microstructures of 20CrNi2Mo steel underneath the contact surface were examined after dry sliding. Scanning Electronic Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Backscattered Diffraction (EBSD) and an ultra-micro-hardness tester were used to characterize the worn surface and dry sliding wear-induced layer. Martensite laths were ultra-refined due to cumulative strains and a large strain gradient that occurred during cyclic loading in wear near the surface. The microstructure evolution in dominant abrasive wear differs from that in adhesive wear. In dominant abrasive wear, only bent martensite laths with high-density deformation dislocations were observed. In contrast, in dominant adhesive wear, gradient structures were formed along the depth from the wear surface. Cross-sectional TEM foils were prepared in a focused ion beam (FIB) to observe the gradient structures in a dry sliding wear-induced layer at depths of approximately 1–5μm and 5–20μm. The gradient structures contained nano-laminated structures with an average thickness of 30–50nm and bent martensite laths. We found that the original martensite laths coordinated with the strain energy and provided origin boundaries for the formation of gradient structures. Geometrically necessary boundaries (GNBs) and isolated dislocation boundaries (IDBs) play important roles in forming the nano-laminated structures.