Crystallographic Texture Control of Niti Alloy by Adjusting the Thermal Gradient of Laser Powder Bed Melting

Abstract

Developing a favorable texture can improve the recoverable strain in polycrystalline NiTi shape memory alloys. Nevertheless, the regulation of the texture in NiTi alloys prepared via additive manufacturing presents a more intricate challenge compared to alloys prepared using conventional thermomechanical method. In this study, a robust <001> texture is developed in NiTi alloys by adjust ing the thermal gradient through the precise control of hatching space and energy density in Laser Powder Bed Fusion (LPBF) parameters. Alloys with this texture manifest a stable and fully recoverable strain of 4.82%. Optimal processing parameters, including a hatching spacing of 24 μm, a forming angle of 90°, and a volume energy density of 139 J/mm3, were obtained. A comprehensive microstructural mechanism is proposed to explain the texture development during the LPBF manufacturing process under varying thermal gradients.

Keywords: Laser powder bed melting, NiTi alloy, martensitic transformation, Shape memory alloys, Texture