Effect of Annealing on the Shape Memory Effect and Mechanical Properties of Laser Powder Bed Fusion NiTi Alloy

The emergence of additive manufacturing technology, particularly laser powder bed fusion, has revitalized NiTi alloy production. However, challenges arise regarding its mechanical properties and diminishing shape memory effect, which hinder its widespread application. Heat treatment has been identified as a method to enhance the performance of metallic materials in the realm of additive manufacturing. This process eliminates residual stress and enhances performance through precipitation strengthening. This study conducted a comprehensive annealing investigation on NiTi alloys to explore the impact of annealing time and temperature on the phase transformation behavior and shape memory performance. The mechanism underlying the performance enhancement was analyzed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and transmission electron microscopy. The findings revealed that different annealing conditions resulted in multistep phase transformation behavior, with the 500 ℃–5 h sample exhibiting the best mechanical properties owing to the formation of nanoscale dispersed precipitates like Ni 4 Ti 3 . However, higher temperatures led to larger precipitates, significantly weakening the properties of the NiTi alloy. Additionally, the annealing treatment did not have a notable impact on the grain size, texture strength, or direction. This study provides valuable insights for optimizing the heat treatment process of LPBF-NiTi alloys.