Influence of Substrate Temperature on Structure and Functional Properties of NiTi Walls Produced by WAAM

The ten-layered NiTi walls were manufactured by wire arc additive manufacturing (WAAM) on Ti substrate pre-heated at 20 °C, 200 °C, 300 °C or 400 °C. It was found that an increase in the substrate temperature increased the sharpness of [001] texture and led to smooth variation in the Ni concentration in the NiTi phase on sample height that affected the martensitic transformation parameters. Annealing at 500 °C for six hours aligned the Ni distribution in the NiTi phase and decreased its concentration due to the formation of Ni4Ti3 precipitates. As a result, starting in the fifth layer, the martensitic transformation temperatures became independent of the distance from the substrate and the substrate temperature. In annealed samples, the substrate temperature affected the shape memory and superelastic behaviour. The recoverable and irreversible strain decreased upon an increase in substrate temperature because they were affected by the texture that was not destroyed by annealing.