On the anisotropy of thick-walled wire arc additive manufactured NiTi alloy part

Bulk NiTi alloy was fabricated via cold metal transfer-based wire arc additive manufacturing (CMT-WAAM) process. This study investigates the microstructure evolution and reveals the correlation between microstructural features and mechanical properties. The results show that B2 austenite elongated columnar grains grow epitaxially parallel to the deposition direction in the center region of NiTi alloy melt pool, columnar grains grow alternately perpendicular to the fusion line in the overlapping region, and equiaxed grains are observed in the top region. Ti-rich NiTi precipitates and Ti₂Ni precipitates are clustered and randomly distributed respectively. The texture intensity of 45° plane crystal is 18.23, and it has strong Cube texture. The average Schmid Factor (SF) value in {011} < 100 > slip system is 0.28. The microhardness value of NiTi alloy bulk along the deposition direction increases with the deposition layer height and tends to be stable, with an average value of about 368.60 HV. The average microhardness along the normal direction is 367.11 HV. The hardness, elastic modulus and indentation recovery rate of the characteristic region near the fusion line are similar. The H0 and D45 samples exhibit high strength and low plasticity, while the V90 sample exhibits low strength and high plasticity.