MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF CR3C2 PARTICULATE-REINFORCED AL2O3 MATRIX COMPOSITES

Al2O3 matrix with three grades of Cr3C2 particle size (0.5, 1.5 and 7.5 mum) composites were fabricated by a hot-pressing technique. Fully dense compacts with Cr3C2 content up to 40 vol% can be acquired at 1400-degrees-C under 30 MPa pressure for 1 h. The flexural strength increases from 595 to 785 Mpa for fine Cr3C2 particle (0.5 mum) reinforced Al2O3 matrix composites. The fracture strength is significantly dependent on the fracture modes of matrix (intergranular or transgranular). The transgranular fracture with a compressive residual stress gives a high fracture strength of composites. At the same time, the fracture toughness increases from 5.2 MPa m1/2 (10 vol% Cr3C2) to 8.0 MPa m1/2 (30 vol% Cr3C2) for the coarse Cr3C2 particle (7.5 mum) reinforced Al2O3 matrix composites. The toughening effects of incorporating Cr3C2 particles into Al2O3 matrix originate from crack bridging and deflection. The electrical conductivity and the possibility of electrical discharge machining of these composites were also investigated.