The interaction effect of process parameters on the phase transformation behavior and tensile properties in additive manufacturing of Ni-rich NiTi alloy

In this work, response surface methodology (RSM), as a reliable and cheap prediction tool, was developed to establish a quadratic regression model between selective laser melting (SLM) process parameters and the martensite transformation temperatures (MTTs) of SLM-NiTi alloys during SLM process. In the case of martensite start temperature (Ms) and austenite finish temperature (A(f)), analyzing the result of RSM illustrated that the average error percentage between the predicted and experimental results are within 7.42 +/- 0.45% and 3.83 +/- 0.23%, respectively. Besides, we show that the interaction of laser power (P) and scanning speed (v) have a remarkable impact not only on MTTs but also on tensile properties and tensile recovery strain of SLM-fabricated NiTi samples. With the decrease of P and the increase of v, the M-s and A(f) decrease, respectively. The tensile experimental results showed that the group of 150 W samples equipped with high elongation, in which the highest elongation up to 12 +/- 0.4%, but the high tensile recovery strain was presented in the 100 W series. This study provided a new-fangled insight for how process parameters modulate phase transformations and mechanical properties in the SLM fabricated NiTi, which can be conducted to target mechanical properties for different applications.