Microstructure, phase transformation behavior and tensile superelasticity of NiTi shape memory alloys fabricated by the wire-based vacuum additive manufacturing

In this work, NiTi shape memory alloys with tensile superelasticity are fabricated by thetechnology of wire-based vacuum additive manufacturing and post heat treatment. This work comprehensively investigates the microstructure, phase transformation behavior and tensile superelasticity, which are all found to be dependent of building height. The as-built NiTi part demonstrates columnar crystals and strong [001] texture along the building direction. For as-built NiTi part, the top region shows lower phase transformation temperatures and better superelasticity, while the middle and bottom regions exhibit higher phase transformation temperatures and poor superelasticity. After heat treatment, the transformation behavior and superelasticity on the building height can be adjusted to be uniform. The results show that wire-based vacuum additive manufacturing is very promising to produce dense and pure NiTi functional structures with good working condition adaptability.