Powder metallurgical processing of Ni–Ti–Zr alloys undergoing martensitic transformation: part I

Ni–Ti–Zr materials with Zr 12–25 at.% and Ni 42–50 at.% have been produced by powder metallurgy. Suitable temperatures for sintering in Ar-atmosphere Ni–Ti–Zr compacts are within the range 900–1000 °C. Sintering at temperatures above 1000 °C causes melting of the compacts with high Zr content. The presence of ZrC, ZrO2, Zr3O, TiO2 and TiO of different modifications, complex oxides such as Ni5TiO7, Ti0.5Zr0.5O0.2 and equilibrium phases after sintering at temperatures above 1000 °C in alloys with low Zr-content was derived from X-ray diffractometry. During sintering at temperatures below 1000 °C the phases belonging to the binary Ti–Ni and Ti–Zr systems were formed. Long-term sintering and slow furnace cooling allowed the precipitation of Ni4Ti3 and Ni2Ti. The process of sintering is controlled by the diffusion of Ni in Ti and Zr particles during the early stages of sintering. Slow diffusion of Zr atoms in Ti2Ni, Ti–Ni and diffusion of Ti atoms in Zr2Ni, Ni–Zr controls the later stages of sintering.