Wear properties of Y-α/β composite sialon ceramics

The tribological properties of yttrium containing alpha/beta composite sialon ceramics have been studied under non-lubricated conditions by means of block-on-ring and ball-on-disk type experiments against a commercial silicon nitride material. The sialon ceramics were produced by hot pressing powder mixtures Of Si(3)N(4), AlN, Al(2)O(3) and Y(2)O(3), resulting in composite ceramics containing different amounts of the alpha/beta phases. The effects of microstructural differences on the mechanical properties of the ceramics, and their wear characteristics under a range of testing conditions have been assessed. It was found that Vickers hardness decreased whilst both fracture toughness and bending strength increased with increasing amount of beta phase in the composite. Under mild testing conditions, material removal was considered to occur by polishing of the surface, and in this case the high alpha-sialon composites exhibited the highest wear resistance, reflecting their higher hardness. Under severe testing conditions, the wear behaviour was characterised as microcracking caused by the higher Hertzian stress levels, and resulted in grain removal or "dropping" from the surface of the materials. Under these conditions, the elongated microstructure and higher fracture toughness of the low alpha-sialon composites hinder the crack propagation and result in better wear characteristics when compared to the fine equiaxed alpha-sialon materials. (C) 2003 Elsevier Science Ltd. All rights reserved.