Ni-Ti-Zr ternary alloy with high transition temperature fabricated by laser powder bed fusion

Abstract

Nitinol alloys have recently drawn significant attention and interest in a broad range of applications, due to their excellent shape memory properties, super elasticity and corrosion resistance. However, the low phase transition temperature of the binary Ni-Ti alloy is difficult to meet the high temperature performance requirements, while adding a third alloying element can dramatically improve the phase transition temperature. Additive manufacturing is an effective means for preparing complex shape memory alloy parts, and laser powder bed fusion (LPBF) technology is the most widely used technology. This paper mainly studies the LPBF process optimization process of Ni-Ti-Zr ternary alloy, and reveals the evolution of microscopic defects, microstructure, phase transformation behavior and mechanical properties in LPBF-formed Ni-Ti-based shape memory alloy through the characterization of microstructure and properties. The optimized process window range is 45–80 J/mm3 with the highest relative density of 98.89% under laser power of 250 W, scanning speed of 1000 mm/s, and the preheat temperature of 200 ℃. The average compressive fracture strength is measured to be 1955.77 MPa, and the average elastic recovery strains under pre-compression deformation of 3%, 6%, and 9% are 2.41%, 4.06%, and 6.56%, respectively. Furthermore, the average peak temperature of B19'→B2 is 99.19 ℃, and that of B2→B19' is 28.99 ℃. Compared with the LPBF-made binary Ni-Ti alloys, the phase transformation temperature and thermal hysteresis of Ni-Ti-Zr alloy have been significantly increased by the addition of Zr. It is expected to broaden the application of nickel-titanium alloys under high-temperature conditions, and provide a theoretical reference for LPBF forming of high-performance nickel-titanium-based shape memory alloys.