Microstructure and mechanical properties of in situ NiAl-Mo2C nanocomposites prepared by hot-pressing sintering

NiAl-based nanocomposites reinforced by in situ Mo2C ceramic precipitates were successfully fabricated by mechanical alloying and hot-pressing sintering. The microstructure and mechanical properties of NiAl-based nanocomposites reinforced by in situ Mo2C ceramic precipitates were investigated. The results showed that the nanostructured powder particles with the average size below 30 nm were successfully obtained by mechanical alloying. After sintering, the composites were constituted of B2-ordered NiAl and in situ Mo2C ceramic precipitates, and the crystallite size of NiAl phase was below 200 nm and Mo2C ceramic precipitates were evenly dispersed in the NiAl-matrix. Mo2C precipitates were formed by the solid-state reaction of C and metallic Mo element during the hot-pressing sintering process. The relative density, hardness and compressive strength of high-density nanostructured NiAl materials increased with increasing Mo content, which can be attributed to the second phase hardening effect of Mo2C ceramic particulates and fine grain strengthening of nanocrystalline NiAl phase. The wear test results showed that the friction coefficient of NiAl-Mo2C nanocomposites at 700 °C (0.35) was significantly lower than that of NiAl alloy (0.48). The improvement of high temperature tribological properties could be attributed to the formation of molybdenum trioxide tribofilm and the second phase hardening effect of Mo2C ceramic particulates.