EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The present work highlights a promising manufacturing route of equiatomic NiTi alloys which is characterized by a short duration mechanical alloying (MA) step (25.0 min at 300 rpm) followed by a spark plasma sintering (SPS) step (750 ºC for 2.5 and 7.5 min, using a pressure of 51 MPa). The processed materials were characterized by X-ray diffraction, scanning electron microscopy, density, and porosity. The results will be discussed regarding to the structural and microstructural modifications observed during the different processing steps and, more specifically, to the formation of the austenitic phase (B2). The short MA step allowed to minimize contamination issues and resulted in high powder yield levels (~79%) with the powder particles having already a layered Ni-Ti microstructure. The high reactivity of the MA powder was responsible by the formation of B2 immediately after SPS. Furthermore, the increase in the SPS holding time from 2.5 min to 7.5 mm induced a decrease in porosity and an increase in the densification. It was also observed an increase in the homogeneity with the apparent reduction of the fraction of NixTiy intermetallics in favor to the NiTi associated with the B2 phase. Such results represent an improvement in the synthesis process of equiatomic NiTi alloys by powder metallurgy.