Investigation on Formation Mechanism of Nano-Gradient Structure in Dry Sliding Wear of Martensite Steel

Dry sliding wear test was carried out on a martensitic steel using a SFT-2M pin-on-disk friction tester. The microstructure after sliding wear was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and microhardness tester. The results show that microstructural change was controlled by different wear mechanisms at both high and low contact loads. At a relatively lower load, martensite lath became bend under the mechanism of abrasive wear, whereas it formed a gradient structure at the mechanism of adhesive wear at the higher load. As a result of sliding wear-induced plastic deformation, high dislocation density of geometrically necessary boundaries (GNBs) and incidental dislocation boundaries (IDBs) was formed. This led to the formation of laminated structure. The lamellar spacing was greatly reduced and grains were partitioned into smaller grains with increasing number of GNBs and IDBs. Eventually, nano-laminated structure was generated.