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

• Microstructure–processing correlations were studied for hot pressed ZrB2 ceramics.
• Significances of temperature and time on grain size were 56 and 33%, respectively.
• Controlling densification mechanisms varied with increasing the hot pressing factors.
• By approaching the optimal state, the fracture surface changed to transgranular mode.

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.