Balanced strength-ductility combination and good recoverable strain of Ni50.7Ti49.3 alloy fabricated by high scanning velocity in selective laser melting

Abstract

Optimizing of process parameters such as high laser power combined with high scanning velocity during selective laser melting (SLM) is appropriate to the demand of high efficiency and high precision fabrication of NiTi alloys. However, the exploration in such process window is inexhaustive yet. In this work, SLM parameters of high laser power combined with high scanning velocity (180 W and 800–1400 mm/s) are adopted to manufacture defect-free Ni 50.7 Ti 49.3 alloy and the microstructure, martensitic transformation, mechanical and functional properties are studied systematically. The microstructure of SLM samples is composed of alternate coarse and fine columnar grains in different regions of molten pool. Unique square grain structure is formed in the top surface. Consequently, the prepared Ni 50.7 Ti 49.3 samples exhibit balanced strength-ductility combination with tensile strength of 804.6–870.0 MPa and ductility of 6.4–8.1%. Good recoverable strain of 3.4%–4.7% and recovery ratio of 83.1%–88.9% is achieved. Basically, the change in the recoverable strain for the prepared samples at different scanning velocities are discussed based on thermodynamics analysis. The findings in this work provide some insights into design and preparation of high-performance NiTi alloys by SLM. • A newly developed selective laser melting parameter window of high laser power combined with high scanning velocity was investigated. • Balanced strength-ductility combination with tensile strength of 804.6–870.0 MPa and ductility of 6.4–8.1% was achieved. • Alternate coarse and fine columnar grains in square grain structure postpone the crack propagation. • Strain recovery via superelasticity or shape memory effect was analyzed based on thermodynamics principle.