Core-rim structure, bi-solubility and a hierarchical phase relationship in hot-pressed ZrB2-SiC-MC ceramics (M=Nb, Hf, Ta, W)

Core-rim structures were identified as a common feature in hot-pressed ZrB2-SiC-MC ceramics (M = Nb, Hf, Ta and W) by a combination of X-ray diffraction, scanning and transmission electron microscopies. Quantitative analyses associate them with the bi-solubility of M in ZrB2 phase, in which transition of solubility across the core/rim boundary is abrupted, signifying their creation via dissolution-reprecipitation process facilitated by transient liquid-phase. The cores were retained from starting powder after surface melting and the rims were grown from the liquid-phase to incorporate more solutes, leaving the residual liquid to turn into ZrC phase with higher solubility of M. We propose g-point scheme in the ZrB2-MB2 diagrams to combine the bi-solubility and the core-rim structures into an intra-phase relationship created by sintering, leading further to a hierarchical phase relationship. The temperature dependence of flexural strength in the ZrB2-SiC-MC ceramics varies with MC additions, which can be respectively strengthened by the strain energy created in the core-rim structures and metal segregation to grain boundaries. (C) 2020 The Chinese Ceramic Society. Production and hosting by Elsevier B.V.

Automated summary

The core-rim structures were identified as common features in hot-pressed ZrB2-SiC-MC ceramics, formed by a dissolution-reprecipitation process facilitated by a transient liquid-phase. These structures, with bi-solubility, strengthen the material and affect the temperature-dependent flexural strength variations in the ceramics.