Deformation mechanism and load transfer in an in-situ NiTi-Nb composite

In this study, the cyclic deformation behaviours of an in-situ Nb nanowire reinforced NiTi shape memory alloy composite were studied by in-situ synchrotron X-ray diffraction measurements. Localized hardening in Nb nanowire and the corresponding localized relaxation in NiTi matrix were detected in the Luders band front upon stress-induced martensitic transformation, indicating a phase load transfer from the transformed NiTi to Nb nanowire. Based on the load transfer, a self-propagating transformation process performing under an average phase stress lower than the critical transformation stress was proposed, which should be responsible for the Luders-like deformation of the composite. The change of deformation mode from Luders-like localized defor-mation to homogeneous deformation after the first tensile cycle was attributed to the plastic deformation in Nb nanowire and the formation of internal stress gradient field in NiTi upon pseudoelastic cycling.

Automated summary

In this study, the cyclic deformation behaviors of an in-situ Nb nanowire reinforced NiTi shape memory alloy composite were analyzed. The results showed localized hardening in the Nb nanowire and corresponding relaxation in the NiTi matrix during stress-induced martensitic transformation. This indicated a phase load transfer from the transformed NiTi to the Nb nanowire. The study also proposed a self-propagating transformation process that occurs under an average phase stress lower than the critical transformation stress, which may be responsible for the Luders-like deformation of the composite. The change in deformation mode from localized deformation to homogeneous deformation after the first tensile cycle was attributed to plastic deformation in the Nb nanowire and the formation of an internal stress gradient field in the NiTi during pseudoelastic cycling.