Significance of hot pressing parameters and reinforcement size on sinterability and mechanical properties of ZrB₂-25 vol% SiC UHTCs

Abstract The influences of hot pressing parameters and SiC particle size on the bulk density, the average ZrB₂ grain size and Vickers hardness of ZrB₂-25 vol% SiC ultrahigh temperature ceramic composites were investigated. In this paper, the Taguchi methodology (An L9 orthogonal array) was used to specify the contributions of four parameters: the hot pressing temperature, holding time, applied pressure and SiC particle size. The experimental procedure included nine tests for four parameters with three levels which were employed to optimize the process parameters. The statistical analyses recognized the hot pressing pressure and temperature as the most consequential parameters affecting the density and hardness of ZrB₂-SiC composites. The SiC particle size and holding time were specified as the most effective parameters on the average ZrB₂ grain size. The bulk density, average ZrB₂ grain size, Vickers hardness and fracture toughness of the sample, hot pressed at optimal conditions (1850°C, 90 min, 16 MPa and 200 nm), reached about 5.36 g/cm³, 10.03 μm, ∼17.1 GPa and 5.9 MPa m^1/2, respectively. The confirmation test, carried out under optimum conditions, showed that the experimental results were relatively equal to the predicted values from the Taguchi prediction model. Finally, the mechanisms of enhanced fracture toughness of the hot pressed ZrB₂-SiC ceramic composites were discussed.