Significance of hot pressing parameters on the microstructure and densification behavior of zirconium diboride

In this study, microstructure-densification relations were investigated for zirconium diboride ceramics. Billets of ZrB₂ were densified by hot pressing at 1700, 1775 or 1850 °C for 30, 60 or 90 min under 8, 12 or 16 MPa. SEM micrographs of polished and fracture surfaces as well as density and porosity measurements were used to study the influences of hot pressing parameters (temperature, dwell time and applied pressure) on the final microstructure and densification behavior of ZrB₂. A design of experiment approach, Taguchi methodology, was used to optimize the hot pressing of ZrB₂. In this way, an L9 orthogonal array procedure, which comprises the signal to noise ratio and the analysis of variance, was employed. The significances of temperature, dwell time, pressure as well as unknown parameters, affecting the mean ZrB₂ grain size, were recognized about 56, 33, 1.5 and 9.5%, respectively. The controlling densification mechanisms were shown to vary from ZrB₂ particles rearrangement to diffusion-based mechanisms with increasing hot pressing factors. In addition, by approaching the optimal hot pressing conditions, the fracture surfaces of the samples changed from intergranular to transgranular state, dominantly.