Effect of CoCrFeNiMn high entropy alloy interlayer on microstructure and mechanical properties of laser-welded NiTi/304 SS joint

In order to suppress the formation of Fe-Ti IMCs in NiTi SMA/304 SS laser-welded joint and improve the properties of the joint. In this study, NiTi SMA/304 SS dissimilar alloys joints with and without CoCrFeNiMn high entropy alloy interlayer were obtained by micro laser welding process. The effect of CoCrFeNiMn high entropy alloy interlayer on the microstructure and properties of NiTi SMA/304 SS laser-welded joint was investigated systematically. Results showed that the addition of HEA interlayer significantly reduced the formation of the brittle intermetallic compounds (IMCs) such as FeTi phase. The addition of high entropy alloy interlayer promotes the formation of (Fe,Ni) solid solution phase, therefor, the joint with HEA interlayer is composed of (Fe,Ni) solid solution and small amount of FeTi IMCs and B2 phase. On the other hand, the average microhardness of weld metal was decreased from 732 HV to 221 HV by adding the HEA interlayer. The addition of HEA interlayer significantly improves the tensile shear properties of the joint, and the tensile shear load of the joint can reached 175 N, which is 6 times higher than that of the joint without HEA interlayer.