Deformation mechanism of defect-free Ni50Ti50 alloys via laser powder bed fusion

Abstract

To fully utilize the functionality of shape memory alloys (SMAs), laser powder bed fusion (LPBF) has gradually become the most dominant preparation method for NiTi SMAs owing to its high geometric adaptability. However, due to the unique microstructure of LPBF parts, the shape memory effect (SME) of SMAs prepared by this method is significantly lower than that of other preparation processes. Improving SME has become a recognized difficult problem. This study investigates that dislocation slip and stable martensite during deformation are the main causes of irreversible strain. Furthermore, for the first time, it was found that the hindering effect of nanoprecipitates relative to dislocation movement in LPBF NiTi SMAs can inhibit the formation of slip bands. This hinders the formation of stable martensite and significantly improves SME (with a maximum tensile strength of 922 MPa, maximum elongation of 10.18%, and recoverable strain of 6.8% after applying 8% strain). These results provide a theoretical basis for enhancing the SME of LPBF-SMAs and offer the possibility for preparing NiTi SMAs smart actuators.