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

Abstract

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 500nm by adjusting different technological parameters. The synthesized BaMoO4 powders have a good thermal stability in air after calcining up to 1100°C for 5h. 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 10wt% or 20wt% 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 10−5–10−6mm3/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.