Laser modified microstructures in ZrB_2 ZrB_2/SiC and ZrC

摘要

Microstructural evolution of spark plasma sintered ZrB_2,ZrB_2/20 vol.% SiC (ZS20) and ZrC ultra high temperature ceramics (UHTCs) duringlaser heating has been investigated. Laser heating at temperatures between 2000 and 3750℃ for up to 300 s, in air or vacuum, resulted in extensivebubble and crater formation on the surfaces of 10 mm diameter samples. However, even after exposure to ultra high temperatures, samples didnot disintegrate. X-ray diffraction of exposed faces of ZrB_2 and ZS20 samples laser heated in air up to 2700 detected only crystalline zirconia.A wide, range of morphologies, including nodules, needles, nanofibres and lamella, were observed. The surface of ZrC samples, laser heated invacuum up to 3750℃, were characterised by dendritic and eutectic morphologies. Other features associated with melting, such as solidificationcracks and trapped porosity, were also observed. A complex array of mechanisms involving solid, liquid and vapour phases led to formation ofthese various morphologies inclg melting, oxidation, volatilisation and liquid flow.