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

Abstract

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.