Fabrication and Mechanical Properties of Al ₂ O ₃ ‐WC‐Co Composites by Vacuum Hot Pressing

Abstract

Al 2 O 3 ‐WC‐Co composites were fabricated by vacuum hot‐pressing mixtures of Al 2 O 3 , WC, and cobalt powders. The phases formed with WC additions of up to 40 wt% were α‐Al 2 O 3 , WC, Co 3 W 3 C, and small amounts of f‐Co (face‐centered cubic cobalt) and carbon (graphite); no cobalt or carbon phases formed at >40 wt% WC. A more‐uniformly distributed and connected WC matrix formed as the WC content increased. The 10Al 2 O 3 ‐80WC‐10Co (in wt%) composite exhibited high bending strength (1250 MPa), fracture toughness (9 MPam 1/2 ), and hardness (20.6 ± 0.5 GPa) simultaneously. The high bending strength was mainly attributed to fewer fracture origins due to the uniformly distributed and connected WC matrix together with a lower porosity. Increased fracture toughness was caused mainly by crack deflection and crack bridging in a uniformly connected WC matrix. High hardness resulted from finer WC metallic compounds and Co 3 W 3 C precipitation in almost all ranges.