Microstructure and tribological properties evolution of Ni–Mo–SrSO4 composites as a function of Mo contents at different temperatures

Abstract

Ni–Mo–SrSO4 composites with different Mo amount were prepared by hot pressing in a vacuum. The oxygen-deficient environment derived from the degradation of SrSO4 during fabrication process led to the formation of SrMoO4, Sr2NiMoO6, and SrO in the sintered composites. With the increment in the contents of Mo, excessive dissolved Mo atoms accelerated the oxidation of Ni in the oxygen-deficient environment, which eradicated SrMoO4 phase. As compared to sintered material containing Sr2NiMoO6 and SrO, the appearance of SrMoO4 led to a distinct decrease in the density and microhardness. To reveal the effect of SrMoO4 on the wear mechanism, the tribological properties of the sintered composites against Al2O3 ball were investigated at different temperatures. The result indicated that the in-situ composite consisting of 80.75 wt.% Ni, 14.25 wt.% Mo, and 5 wt.% SrSO4 exhibited good friction and wear properties at room temperature (RT) and 800 °C, which was attributed to the development of the intact tribofilm with grooves consisting of SrMoO4, Sr2NiMoO6, NiO, and h-MoO3 at RT and the synergistic lubricating effect of SrMoO4, Sr2NiMoO6, and oxides (NiO, α-MoO3, SrMoO4, α-NiMoO4, and β-NiMoO4) at 800 °C.