Effect of Nb content in the microstructural and thermal characteristics of NiTiNb shape memory alloys

The influence of Nb content variation on the microstructural and thermal characteristics of NiTiNb alloys was evaluated since these aspects are relevant to the control and adequacy of its shape memory properties for application purposes. The aim of this study was to observe how the Nb content acts in the formation of Nb-rich precipitates and the eutectic structures, which can make this alloys more complex. Microstructural characterization of the alloys was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microanalysis by energy-dispersive X-ray spectroscopy (EDS), besides the thermal characterization by differential scanning calorimetry (DSC), and the comparison between the Nb alloys and the NiTi binary alloy. The results demonstrated a proportional dependence between the amount of β-Nb phase in the microstructures and the amount of Nb dissolved in the NiTi matrix with the Nb content. Although it was found that the increase in the Nb content causes the decrease of the martensitic (Mi) and reverse (Ai) transformation temperatures, the magnitude of thermal hysteresis was not significantly changed. (author)