Effects of laser processing on the transformation characteristics of NiTi: A contribute to additive manufacturing

Laser additive manufacturing of NiTi generates complex microstructural features not fully understood yet. Thermal similarities between laser microjoining and laser additive manufacturing, enables correlating the effect of the laser on the material in both processes. To clarify them, a simplified yet accurate approach was employed: in-situ X-ray diffraction was used to determine the local transformation temperatures along the thermally affected regions in a laser processed NiTi thin sheet. The observed gradient of transformation temperatures is related to local chemical compositional changes through Ni depletion and residual stresses, explaining the peculiar microstructural and mechanical features observed in additive manufacturing of NiTi.