Wear properties of self-reinforced α-SiAlON ceramics produced by spark plasma sintering

Previous work had shown that in wear of composite SiAlON ceramics, materials with high fracture toughness (high β content) showed better wear resistance under high loads. However, under low loads single phase α materials showed better wear properties. This has led to a strategy of producing materials suitable for a range of wear conditions through developing self-reinforced microstructures consisting of elongated grains in single phase α-SiAlON. In this work, these new types of tough α-SiAlON ceramics have been produced by spark plasma sintering (SPS) and their wear properties assessed through block on ring wear tests under dry conditions. The microstructures of the samples were tailored through adjusting chemical compositions and/or exploiting the grain growth kinetics, and resulted in materials with microstructures ranging from equiaxed to coarse elongated α grains. The mechanical properties showed a slight decrease in hardness but around a doubling of fracture toughness with increasing grain size. Under high load wear conditions where mechanical wear occurs through the propagation of intergranular microcracks, the wear rate decreased with increasing grain size due to the higher fracture toughness helping to prevent crack propagation. Under low load wear tests, where tribochemical reactions are thought to play an important role in the wear mechanism, the samples all showed very similar wear rates. The results showed that the coarse grained elongated α material shows good wear properties over a wide range of loads.