Synthesis, microstructure and mechanical properties of Cr2AlC/Al2O3 in situ composites by reactive hot pressing

Al2O3 particle-reinforced Cr2AlC in situ composites were successfully fabricated from powder mixtures of Cr3C2, Cr, Al, and Cr2O3 by a reactive hot-pressing method at 1400 °C. A possible synthesis mechanism was proposed to explain the formation of the composites in which Al2O3 was formed by the aluminothermic reaction between Al and Cr2O3, meanwhile, Cr3C2, Al, together with Cr reacted to form Cr2AlC in a shortened reaction route. The effect of Al2O3 addition on the microstructure and mechanical properties of Cr2AlC/Al2O3 composites was investigated. The results indicated that the as-sintered products consisted of Cr2AlC matrix and Al2O3 reinforcement, and the in situ formed fine Al2O3 particles dispersed at the matrix grain boundaries. The flexural strength and Vickers hardness of the composites increased gradually with increasing Al2O3 content. But the fracture toughness peaked at 6.0 MPa m1/2 when the Al2O3 content reached 11 vol.%. The strengthening and toughening mechanism was also discussed.