Phase transformation in Fe–Mn–Si SMA/WC composite coating developed by laser cladding

Abstract

A Fe–Mn–Si shape memory alloy/nano-WC (SMA/WC) coating was prepared by laser cladding on the surface 304 stainless steel. The phase composition, stress-induced phase transformation mechanism, microstructure, microhardness and wear resistance were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microhardness tester and friction tester, respectively. Results show that γ austenite, ε martensite and Fe6W6C phase appear in the composite coating, and the coating is composed of planar crystals, cell crystals, fine dendritic crystals and fine equiaxed grains from binding zone to surface region. The residual stress leads to the entanglement and accumulation of dislocations in the austenite grain boundaries, which in turn induce martensite deformation. The martensite phase of the annealed composite coating disappeared, and the microstructure showed austenite morphology. The SMA/WC coating has higher microhardness and excellent wear resistance due to the occurrence of γ austenite → ε martensite transformation. Furthermore, the addition of WC increases the microhardness of the coating by more than 2 times, and reduces the friction coefficient and the wear loss by about 1/4 and 2/3 respectively.