Fracture toughness of advanced alumina ceramics and alumina matrix composites used for cutting tool edges

Purpose: Specific characteristics in fracture toughness measurements of advanced alumina ceramics and alumina matrix composites with particular reference to α-Al2O3, Al2O3-ZrO2, A2O3-ZrO2-TiC and AI2O3-Ti(C,N) has been presented. Design/methodology/approach: The present study reports fracture toughness obtained by means of the conventional method and direct measurements of the Vickers crack length (DCM method) of selected tool ceramics based on alumina: pure alumina, alumina-zirconia composite with unstabilized and stabilized zirconia, alumina-zirconia composite with addition of TiC and alumina-nitride-carbide titanium composite with 2wt% of zirconia. Specimens were prepared from submicro-scale trade powders. Vicker’s hardness (HV1), fracture toughness (KIC) at room temperature, the indentation fracture toughness, Young’s modulus and apparent density were also evaluated. The microstructure was observed by means of scanning electron microscopy (SEM). Findings: The lowest value of KIC is revealed by pure alumina ceramics. The addition of (10 wt%) unstabilized zirconia to alumina or a small amount (5 wt%) of TiC to alumina-zirconia composite improve fracture toughness of these ceramics in comparison to alumina ceramics. Alumina ceramics and alumina-zirconia ceramics reveal the pronounced character of R-curve because of an increasing dependence on crack growth resistance with crack extension as opposed to the titanium carbide-nitride reinforced composite based on alumina. R-curve has not been observed for this composite. Practical implications: The results show the method of fracture toughness improvement of alumina tool ceramics. Originality/value: Taking into account the values of fracture toughness a rational use of existing ceramic tools should be expected.