Formation mechanism of inherent spatial heterogeneity of microstructure and mechanical properties of NiTi SMA prepared by laser directed energy deposition

Abstract Ni 51 Ti 49 at.% bulk was additively manufactured by laser-directed energy deposition (DED) to reveal the microstructure evolution, phase distribution, and mechanical properties. It is found that localized remelting, reheating, heat accumulation during DED leads spatial heterogeneous distribution of columnar crystal equiaxed crystal, a gradient 4 3 precipitates along building direction, preferential formation in zone. The austenite transformation finish temperature ( A f ) varies from −12.65 °C Z = 33 mm) 60.35 10 mm), corresponding tensile yield strength σ 0.2 changed 120 ± 30 MPa 570 20 MPa, functional properties shape memory effect superelasticity at room temperature. sample 20.4 mm height has best plasticity 9.6% recoverable strain 4.2%. This work provided insights guidelines for characterization DEDed NiTi.