Influence of the nickel contents and sintering pressure on microstructure and tribological properties of NiTi alloy prepared by Spark Plasma Sintering

Abstract:

In this investigation, NiTi alloys were prepared by high-energy milling and spark plasma sintering (SPS) at 1000℃. The effects of the Ni content and sintering pressure on the density, microstructure, microhardness and tribological properties of NiTi alloys were also investigated. The experimental results showed that the particle sizes of the powders were decreased after high-energy ball milling, and the diffraction peaks of Ni phase were shifted to the high angle with the increase of nickel contents. As the sintering pressure increased, the relative densities of NiTi alloys were increased. At the sintering pressure of 5MPa, the relative densities of NiTi alloys were decreased from 94.7% to 84.6% with the increase of nickel contents. When the sintering pressure was higher than 5MPa, the relative densities of NiTi alloys were firstly increased and then decreased as nickel content increased. However, the lowest value of the relative density of NiTi alloys was happened at nickel content of 45 wt.%. NiTi phase, NiTi2 phase and Ni3Ti phase were presented in the microstructures of NiTi alloys. The microhardness of the alloy were firstly increased and then decreased as the nickel contents increased from 0 wt.% to 65 wt.%. The microhardness of the NiTi alloy has the biggest value at nickel content of 45 wt.%. The wear rates of NiTi alloys were reduced as the nickel content and sintering pressure increased and the wear resistance of the alloys were significantly improved. The wear mechanisms of NiTi alloys at room temperature were mainly abrasive wear and adhesive wear.

Key words:Nickel content; sintering pressure; NiTi alloy; microstructure; tribological properties