Effects of Solid Solution Treatment on the Microstructure and Wear Resistance of a Laser Cladding Fe-Mn-Si/WC/Y2O3 Shape Memory Alloy (SMA) Composite Coating

A Fe-Mn-Si/WC/Y2O3 shape memory alloy (SMA) composite coating was prepared by fibre laser cladding onto the surface of 304 stainless steel. The difference in microstructure and wear resistance of the SMA composite coating and the solution treated Fe-based shape memory alloy (SSMA) composite coating was studied. The microstructure, phase composition, hardness and wear resistance of the composite coatings were investigated by a scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness tester and friction wear tester, respectively. The results show that microstructure of the crack-free SMA and SSMA composite coating consist of epsilon-martensite, gamma-austenite and Fe6W6C phase, the solution treatment causes forming a large number of second phase of Fe6W6C in the grain boundary and inner. Microhardness and wear resistance of SMA coating are obviously improved to compare with the substrate. Both SMA and SSMA composite coatings have solid solution treatment induced Fe6W6C phases appeared in the crystal and crystal boundary. The second phase makes the hardness increase significantly, but the precipitates destroy the original continuity of microstructure of the coating, bring in cracks and holes in SSMA composite coating, limiting the phase transition of shape memory alloys reducing the stress self-accommodation characteristic, which reduce the wear resistance of SSMA composite coating.