Interfacial phenomena and formation of nano-particles in porous ZrB2-40Â vol% B4C UHTC

The micro/nanostructural development, sintering process and its controlling mechanisms as well as the interfaces between ZrB2 and B4C particles were investigated using high resolution SEM, XRD and TEM analyses in a hot pressed ZrB2-40 vol% B4C ceramic composite. Two types of porosities (open and closed) were observed in the microstructure of fabricated porous composite, which were caused by different factors. The results showed that the sintering process was encouraged by the formation of liquid phases at the interfaces, elimination of oxide impurities from the surfaces of ZrB2 particles (due to the chemical reactions with B4C particles and their free carbon), plastic deformation of ZrB2 grains and the diffusion of carbon and/or boron atoms from B4C toward ZrB2 particles. A mixture of nano-particles and nano-porosities at the submicron thickness amorphous ZrB2/B4C interfaces is detected and discussed in detail.