Mechanical and functional properties of HfH2-decorated NiTi shape memory alloy fabricated by laser powder-bed fusion

Laser powder-bed fusion has been widely utilized to produce complex NiTi devices because of relatively better surface finish and geometrical accuracy. However, NiTi alloys fabricated by laser powder-bed fusion suffer from strength degradation and unstable shape recovery behavior induced by the formation of pore defects and the variation of martensitic transformation, respectively. In this work, the mechanical and functional properties of HfH2-decorated NiTi shape memory alloy fabricated by laser powder-bed fusion have been investigated. Through careful clarification of the effects of microstructure characteristics on mechanical and functional properties, it is concluded that the addition of Hf (<5 at%) efficiently strengthens the NiTi matrix and thus eliminates strength degradation induced by pore defect formation. Moreover, the addition of Hf (<5 at%) into the NiTi matrix weakens martensitic transformation variation through improvement of the critical stress to induce martensitic transformation, resulting in stability enhancement of shape recovery behavior.