Influence of LPBF Parameters and Post-Annealing Temperature on Martensitic Transformation and Superelasticity of Ni-Rich Ni51.9Ti48.1 Alloy

Laser powder bed fusion (LPBF) technology offers an effective approach for fabricating high-performance superelastic NiTi alloys. This study achieved Ni51.9Ti48.1 alloys with outstanding superelastic properties through a triple optimization design of the initial powder composition, printing process parameters, and post-processing. The phase transformation behavior and microstructure of the alloys were systematically investigated. The results indicate that as energy density increases, the size and quantity of pore defects in LPBF-fabricated Ni51.9Ti48.1 alloys increase, phase transformation temperatures rise, and hardness conversely decreases. Ni51.9Ti48.1 alloys produced at lower energy densities exhibit fewer dislocations. After annealing at 600 °C, Ni4Ti3 and R phases form internally, resulting in a maximum superelasticity of 6.64%. Conversely, Ni51.9Ti48.1 alloys produced at higher energy densities exhibited a large number of dislocations and formed subgrains after annealing at 600 °C. Additionally, due to the high void volume fraction, they demonstrated deteriorated superelasticity.