Use of infrared thermography for inspection of tensile deformation of Ti-25Nb-0.5O and Ti-25Nb-0.5N shape memory alloys

This work concerns thermomechanical behavior of two Ni-free Ti-based shape memory alloys (SMAs) doped with nitrogen and oxygen subjected to tensile loading at strain rate of around
0.02 1/s. During the experiments, an infrared camara was used to investigate thermal effects accompanying deformation of the Ti–25Nb–0.5O and Ti–25Nb–0.5N SMAs. Simultaneously, digital image correlation (DIC) served to determine kinematic fields of these alloys in tension. The stress or temperature-induced martensitic transformation from the cubic β phase to the orthorhombic α″ phase is responsible for superelasticity or shape memory effect in the Ni-free Ti-based SMAs [1]. However, the addition of the oxygen and nitrogen interstitials changes tensile characteristics of these SMAs. For instance, the Ti–25Nb SMA exhibits shape memory effect and a Lüders-type deformation [2]. However, stress-strain plots of the Ti–25Nb–0.5O and Ti–25Nb–0.5N SMAs show hysteretic behaviors characterized by superelasticity combined with an increased transformation stress. Our results show that infrared thermography is a useful tool to locally track peculiar temperature changes of these Ni-free Ti-based SMAs. The temperature fields captured at selected stages of loading revealed heat sources associated with the dissipative processes. The thermal effects were discussed in view of the kinematic characteristics obtained using DIC as well as microstructural features and phase content analyses of the SMAs.