Study on the junction zone of NiTi shape memory alloy produced by selective laser melting via a stripe scanning strategy

Abstract In our previous study, NiTi shape memory alloy with excellent tensile properties (total elongation up to 15.6%) was fabricated by selective laser melting (SLM) through a stripe scanning strategy. Junction zone is inevitable in the SLM-fabricated NiTi parts produced using the stripe scanning strategy, which appears between adjacent stripes, and the thermal history of the junction zone is significantly different from that of other areas. In this study, the microstructure, phase transformation behavior, and mechanical properties of the junction zone and non-junction zone were studied. Compared with the non-junction zone, the junction zone exhibits higher phase transformation temperatures and hardness. The refinement of microstructure, more random crystallographic orientations and high-density of pore defects are observed in the junction zone of the SLM-fabricated NiTi alloy. Besides, we studied the effect of different sizes of the junction zone on the tensile mechanical properties of the SLM-NiTi alloy. It is demonstrated that the fracture strength of SLM-NiTi alloy increases with the increase of the proportion of the junction zone. In this work, we discussed the mechanisms of the phenomena in detail.