文摘
A type of Al2O3-based composite ceramic tool material simultaneously reinforced with micro-scale and nano-scale TiC particles was fabricated by the hot-pressing technology with different contents of cobalt additive. The experimental results showed that the Al2O3/TiC micro-nano-composite containing 3 vol % Co, which was sintered under a pressure of 32 MPa at 1650 ¡ãC in vacuum for 20 min, had optimal mechanical properties. Its flexural strength, fracture toughness and hardness were 916 MPa, 8.3 MPa m1/2 and 18 GPa, respectively. The relationships between the mechanical properties and microstructure were discussed. The mechanical properties of the composites increased and then decreased with the increase of the cobalt content. Low content of cobalt led to a poor relative density and excess cobalt caused micro-cracks at the grain boundaries, which decreased the mechanical properties of the composites. The existence of interphase cobalt could effectively decrease the stress concentration and the value of tensile stress in Al2O3 matrix. Both the micro-scale and nano-scale TiC particles contributed to the improvement of the flexural strength and fracture toughness of the composites. The intragranular nano-scale TiC particles influenced the ratio of grain boundary toughness to the grain toughness, leading to an appropriate percentage of transgranular fracture grains. The micro-scale TiC particles could not only enhance the ultimate damage stress of Al2O3 matrix, but also deflect and bridge the cracks.
