Microstructure, Mechanical Properties, and Martensitic Transformation in NiTi Shape Memory Alloy Fabricated Using Electron Beam Additive Manufacturing Technique

Abstract The electron beam additive manufacturing (EBAM) method was applied in order to fabricate rectangular-shaped NiTi component. process performed using an welding system wire feeder inside the vacuum chamber. containing 50.97 at.% Ni and showing martensitic transformation near room temperature used. It allowed obtain a good quality material consisting of columnar grains elongated into built direction growing directly from substrate, which is related epitaxial grain growth mechanism. As manufactured showed reverse transformations diffused over range −10 44 °C, aging at 500° C moved higher temperatures peaks became sharper. highest recoverable strain about 3.5% obtained as-deposited sample deformed along deposition direction. In case deformation alloy aged 500 °C for 2h, formation martensite occurs significantly lower stress; however, 2.5% stress begins increase gradually only small shape recovery observed due temperature. situ SEM tensile perpendicular that began appear surface boundaries heterogeneous nucleation. studies determine following crystallographic relationships between B2 B19’ martensite: (100) ||(100) || (011) ; (011)B2|| (001) $${(011)}_{\mathrm{B}2}||{\left(11\bar{1 }\right)}_{\mathrm{B}1{9}^{\mathrm{^{\prime}}}}$$ (011)B2||111¯B19′ . Samples exhibited fully austenitic microstructure; with increasing degree deformation, observed. majority needles were tilted 45° respect direction, presence type I (11 $$\bar{1 }$$ xmlns:mml="http://www.w3.org/1998/Math/MathML">1¯ ) invariant twin degrees deformation.