Synthesis and tribological properties of ultrafine Cr<sub>2</sub>AlC MAX phase

A microwave hybrid heating method was used for the synthesis of Cr2AlC powder using two carbon sources of graphite and Cr3C2, and tribological behaviour of Cr2AlC powders was investigated. The purity of Cr2AlC is sensitive to the synthesis temperature and the starting materials used. For a Cr/Al/C system, Cr2AlC with a small amount of Cr7C3 was synthesised at 1100°C for 3 min. For Cr/Al/Cr3C2 system, high purity Cr2AlC was synthesized at 1050°C for 3 min. Ultrafine Cr2AlC powder with a grain diameter of less than 500 nm (denoted by u-Cr2AlC) could be prepared by ball-milling and ultrasonic treatment. The tribological properties of as-synthesised and ultrafine Cr2AlC powders as an additive in 150SN base oil were evaluated by an MMW-1A four-ball friction and wear tester. The results show that the base oil containing 2 wt % Cr2AlC presented good tribological performance under a load of 300 N. In addition, the particle size plays an important role in the tribological performance. Ultrafine Cr2AlC powder shows a better tribological performance than MoS2 and as-synthesised Cr2AlC. The improved tribological properties of the u-Cr2AlC sample could be attributed to the formation of a tribo-film under friction.