Multi-scale pseudoelasticity of NiTi alloys fabricated by laser additive manufacturing

Pseudoelasticity behaviors have been found in the NiTi alloys fabricated by laser additive manufacturing (LAM) processes. Reported investigations of pseudoelasticity in LAM fabricated NiTi alloys mainly focus on the effects of laser input energy and post-heat treatments on phase transformation behaviors. The pseudoelasticity behaviors can be affected by the significantly different load-contact conditions in various industrial applications. However, there are no reported investigations of pseudoelasticity behaviors of NiTi alloys fabricated by LAM in different load-contact conditions. For the first time, multi-scale indentation tests at three scales (nanoscale, microscale, and macroscale) are conducted to evaluate and compare the pseudoelasticity behaviors of the NiTi alloys fabricated by LAM in this investigation. In addition, the effects of microstructural features and phase constituents on pseudoelasticity are discussed. Overall, pseudoelasticity at the nanoscale is the best in terms of the smallest remnant depth ratios, followed by that at the macroscale and that at the microscale. Moreover, pseudoelasticity at the nanoscale improves with the increase of load or the number of cycles. As a comparison, pseudoelasticity at the microscale stays steady with the increase of load and decreases with cycling, and pseudoelasticity at the macroscale stays steady with the increase of load or the number of cycles. It is also found that the improvement in pseudoelasticity leads to decreases in apparent hardness and Young's modulus.