Effect of the Ta addition on densification and mechanical properties of NbTi alloys prepared by SPS

Highlights: • Using SPS can prepare NbTi-xTa alloys with a density of more than 99%, which decreases with the increase of Ta content. • The added of Ta not only inhibits the grain growth but also suppresses the precipitation of HCP phase. • The grains size of NbTi-xTa alloys dropped from 57μm to 46 μm at the SPS state and from 94 μm to 76 μm after heat treatment. 2% Ta can make the solid solution phase change the preferred orientation growth of crystal face, from (110) to (211). -- Abstract: In this study, we have fabricated a highly compact NbTi-xTa (x = 0, 1, 2) alloy was fabricated by spark plasma sintering (SPS) using the NbTi powder produced by the plasma rotation electrode process (PREP) and Ta powder produced by the sodium reduction method. Afterward, the alloy samples were subjected to diffusion heat treatment. The microstructure and phase compositions of the NbTi-xTa (x = 0, 1, 2) alloys were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Furthermore, we assessed the microhardness and compression properties of the samples. The results showed that sintering temperature and the Ta content were the key factors that affected the densification. Moreover, with the Ta content increase, the compactness of the alloy slightly decreased, while the microhardness increased. It was also indicated that the Ta addition of suppressed the grain growth and changed the NbTi solid solution from the original (110) surface to the (211) surface after the heat treatment. The first-principles calculation also showed that the Ta addition further stabilized the BCC structure of the NbTi alloy, and it was challenging to prepare HCP precipitates, such as α-Ti.