Fabrication and high-temperature tribological properties of self-lubricating NiCr-BaMoO4 composites

In the present work, NiCr-BaMoO4 self-lubricating composites have been fabricated by hot pressing to evaluate their tribological properties at elevated temperatures. Hydrothermal synthesis method has been used to prepare fine BaMoO4 spherical powders with a size of 500 nm by adjusting different technological parameters. The synthesized BaMoO4 powders have a good thermal stability in air after calcining up to 1100 °C for 5 h. The friction and wear properties of NiCr-BaMoO4 composites were investigated by using a ball-on-disk friction and wear tester in sliding against Si3N4 ball up to 600 °C. As contrasted with unmodified NiCr alloy, the composites incorporated with 10 wt% or 20 wt% BaMoO4 exhibit distinct improvements in effectively reducing friction and wear at elevated temperatures. NiCr-BaMoO4 composites have low friction coefficients of 0.26-0.30 and small wear rates in the order of magnitude of 10−5-10−6 mm3/Nm at elevated temperatures. A dense oxidized surface layer is formed on the worn surface of NiCr matrix composites incorporated with BaMoO4. Tribo-oxidation reaction during high temperature wear tests is responsible for the formation of dense oxidized surface layer containing BaMoO4, NiCr2O4, NiO and Cr2O3. The coupled Si3N4 ball is covered with a transfer layer containing BaMoO4, which effectively reduces the friction and wear.