Effect of whisker orientation on the friction and wear behaviour of Al2O3/TiB2/SiCω composites in sliding wear tests and in machining processes

Abstract

The use of various particle and whisker additions to ceramic matrices provides great improvements in the mechanical properties. The addition of TiB2 particles to an Al2O3 matrix improves the fracture toughness, hardness and strength over monolithic Al2O3, and of advantages with respect to the wear and fracture behaviour when used as a cutting tool material; further improvements in this composite have been made through additions of SiC whiskers. In this paper, sliding wear and cutting tests were employed to determine the effect of whisker orientation on the friction and wear behaviour of an Al2O3/TiB2/SiCω composite. It was found that the friction coefficient and wear rate of this composite varied on the surface with the direction angle θ normal to the hot-pressing direction when sliding against hardened steel. The maximum friction coefficient and wear rate were observed when a θ = 0° surface was used as the wear face at 25, 200, 400 and 600°C, and the minimum values were observed at θ = 90°. The mechanisms responsible were determined to be the strong atom bonding between SiC and Fe, and the whisker pullout from the matrix of the composite. The adhesive wear and whisker pullout were greatly reduced as the angle θ increased. The cutting test results agreed well with the results from the sliding wear tests. It is suggested that the surface with maximum wear resistance (θ = 90° surface) should be chosen as the wear surface in practical uses.