Functional Properties of the Multilayer NiTi Alloy Produced by Wire Arc Additive Manufacturing

The paper is aimed to study the functional properties in the layered NiTi sample produced by wire arc additive manufacturing (WAAM). The experimental studies were carried out using two types of samples: including the Ti–rich and Ni-rich layers or including Ni-rich layers only. The obtained results showed that the existence of the Ti–rich NiTi layer affected the two-way shape memory effect, which was two times higher than the sample including the Ni-rich NiTi layers only. This was due to the additional internal stress formed during preliminary deformation on the border between the Ti–rich and Ni-rich NiTi layers. It was found that the existence of the Ti–rich NiTi layer suppressed the initiation of superelastic response because the stress-induced martensite remained stable on unloading. It was observed that excluding the Ti–rich NiTi layer from the deformation allowed to reveal the superelasticity effect. It was also noticed that the value of the maximum recoverable strain did not exceed 4%, which was 2–2.5 times less than in the NiTi samples produced by conventional technologies. It was assumed that a small recoverable stain was caused by the texture and a small strain up to failure.