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

The effect of the interaction between SrO and SrAl 4 O 7 with monoclinic and/or orthorhombic structures on the tribological performance of NiCr-Al 2 O 3 composites was evaluated over a wide temperature range. The results indicated that the formation of SrO and SrAl 4 O 7 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-SrAl 4 O 7 , SrO and oxides (NiCr 2 O 4 , NiO, and Cr 2 O 3 ) endowed the sintered composites with low friction coefficient and wear rate. When the temperature was above 600 °C, the tribolayer containing monoclinic-SrAl 4 O 7 , orthorhombic-SrAl 4 O 7 and oxides exhibited better tribological properties than the tribofilm consisting of monoclinic-SrAl 4 O 7 , SrAl 12 O 19 and oxides. Furthermore, at 800 °C, the appearance of orthorhombic-SrAl 4 O 7 on the worn surface led to a low friction coefficient and wear rate.