Tribological Properties of In Situ-Fabricated NiCr-Al₂O₃ Composites with SrAl₄O₇ and SrO at Elevated Temperatures

The effect of the interaction between SrO and SrAl₄O₇ with monoclinic and/or orthorhombic structures on the tribological performance of NiCr-Al₂O₃ composites was evaluated over a wide temperature range. The results indicated that the formation of SrO and SrAl₄O₇ with monoclinic and/or orthorhombic structures was effective in improving the friction and wear properties of the sintered composites at elevated temperatures. At 400 °C, the monoclinic-SrAl₄O₇, SrO and oxides (NiCr₂O₄, NiO, and Cr₂O₃) endowed the sintered composites with low friction coefficient and wear rate. When the temperature was above 600 °C, the tribolayer containing monoclinic-SrAl₄O₇, orthorhombic-SrAl₄O₇ and oxides exhibited better tribological properties than the tribofilm consisting of monoclinic-SrAl₄O₇, SrAl₁₂O₁₉ and oxides. Furthermore, at 800 °C, the appearance of orthorhombic-SrAl₄O₇ on the worn surface led to a low friction coefficient and wear rate.