Microstructure and tribological properties of laser directed energy deposited 316-NiTi heterogeneous bionic sandwich structure coatings

Abstract

In this study, inspired by multilayer structures in nature, an equal weight ratio Ni/Cu composite sandwich specimen was introduced for joining 316 and NiTi alloys to improve the wear resistance of 316. The microstructural evolution process as well as the wear resistance mechanism is clarified by a series of material characterization methods and mechanical property tests. The microstructure of the Ni/Cu interlayer exhibits a dendritic morphology, and the NiTi layer shows both coarse and fine characteristics. The crystallography of 316-Ni/Cu–NiTi composite sandwich specimens was investigated by electron backscatter diffraction. Three types of friction balls (316, 440C, 100Cr6) were used to perform dry reciprocating sliding ball-on-plate wear testing on 316-Ni/Cu–NiTi composite sandwich specimens and 316 substrates under varying normal loads from 10 N to 30 N. The 316-Ni/Cu–NiTi specimens showed better wear resistance compared to the 316 substrate under different wear conditions, when the normal load is 30 N and the friction ball is 100Cr6, the specific wear rate of the coating is only 44% of the substrate. This study not only provides insights to enhance the wear resistance of 316, but also develops a novel approach to broaden the connection between austenitic stainless steel and NiTi alloys.