Tribological behaviour of Al2O3/ZrO2-ZrO2 laminated composites

Laminated composites were prepared in the system Al2O3-ZrO2. Starting from sheets produced by tape casting a symmetric structure was obtained by superimposing alternated layers of Al2O3/ZrO2 composite and ZrO2. Due to the different thermal expansion coefficients and shrinkage of the two materials the alumina/zirconia external layers of the samples exhibit a compressive residual stress which leads to an improved apparent surface toughness. The value of this stress was determined by indentation technique. The tribological behaviour of the laminated composites and of a stress free material, with the same composition of the external layers, was assessed by Pin-on-Disc method at different loads and sliding speeds. The effect of differences in properties and microstructural features among the different materials on wear and friction were determined and discussed. Possible wear mechanisms are proposed. In spite of the increased surface toughness in the range of the experimental conditions considered, the presence of compressive residual stresses at the surface does not lead to an improvement of wear resistance in the laminated structure.