Improved tribological performance of nickel based high temperature lubricating composites with addition of metallic oxides

NiCr–Mo–Bi₂O₃/TiO₂ composites were prepared by vacuum hot-press sintering technology. The oxides of Bi₄Ti₃O₁₂, Cr₂O₃ and Ti₂O₃ were formed by the reaction of Cr, Bi₂O₃ and TiO₂ during the sintering process. The intensity of Bi₄Ti₃O₁₂, Cr₂O₃ and Ti₂O₃ diffraction peaks became higher with the incremental content of Bi₂O₃ and TiO₂. Mo element was mainly distributed in the matrix, which had the effect of solid solution strengthen in the composites. The microhardness and yield strength improved with addition of Mo. With Bi₂O₃ and TiO₂ adding, the microhardness obviously increased. The microhardness of NiCr–10Mo–30Bi₂O₃/TiO₂ composite was the highest of 491.6 HV. Nevertheless, the yield strength and ultimate strength significantly decreased. It may be caused by cracks in the interface between metallic oxides and matrix, where stress concentration would occur. The NiCr–10Mo–20Bi₂O₃/TiO₂ composite had the lowest wear rate of 2.1 × 10⁻⁵ mm³/Nm, which was probably due to the oxidation layer was very dense and was very hard to shed in the process of friction. The composites after adding of Bi₂O₃ and TiO₂ presented the excellent tribology property due to the fact that the Bi₄Ti₃O₁₂ formed on the worn surfaces which had been proved to be an outstanding lubricant at high temperature.