Reactive hot pressing of ZrB2-based composites with changes in ZrO2/SiC ratio and sintering conditions. Part II: Mechanical behavior

ZrB2-based ultra-high temperature composites reinforced with SiC and nano-ZrO2 particles were hot pressed. Taguchi method was used in order to investigate the effect of ZrO2/SiC volume ratio as well as the hot pressing parameters on the mechanical behavior of the composites. The significance of each parameter over the relative density and Vickers hardness of the hot pressed composites and also, optimum conditions to get a composite with maximum relative density and hardness were estimated according to the statistical analyses. The highest Vickers hardness of ~15.4 GPa was achieved for the composite with ZrO2/SiC ratio of 0.2 hot pressed at 1850 °C for 90 min under 12 MPa. Mentioned parameters were found to be the optimum condition for the Vickers hardness proposed by Taguchi method. A fracture toughness of 6.7 MPa m2 was also measured for the mentioned composite which was nearly fully densified (98% relative density) at optimum conditions. Crack deflection, crack branching, microcracking and crack arresting were found to be the dominant toughening mechanisms contributing in the fracture toughness enhancement.