Study on Microstructural Evolution and Compression Performances of Selective Laser Melting NiTi Alloy

Selective laser melting (SLM) technology was adopted to manufacture dense NiTi alloys with different energy densities.The influence rules of the microstrcture characteristics of the matrix phase and precipitation phase on the quasi-static compression and high-stress super-elasticity were studied.The results show that high-quality deposition surface is acquired at 55.56-66.67 J/mm³, and the surface roughness is gradually improved with the energy density increasing. The as-deposited microstructure is characterized by coarse columnar B2 austenite containing dense needle-like B19' martensite. Besides, nano-sized Ti₂Ni phases are precipitated at the martensitic grain boundaries and the grain interiors.The enhanced compression stress is ensured due to the combined strengthening mechanisms of grain refinement and phase precipitation.The compression failure behavior is regarded as rapid shear fracture mode. The excellent super-elasticity performance is acquired, which is attributed to both elastic rebound and martensitic rebound during the unloading period. Conclusively, the excellent microstructural and compressive stability of SLM NiTi parts is ensured within the appropriate processing window.