A study on commercial SiC-powders sintered by hot pressing
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Hot-pressing of a commercial silicon carbide powder was performed with 0, 5 and 10wt% added hexagonal boron nitride. Density, microstructural and compositional development has been studied ex situ with different holding times at sintering temperature. Although other authors have reported poor sinterability for this type of composite, hot-pressing was shown to result in >99% dense materials. Grain growth was restrained, and X-ray diffraction showed no other phases or compounds than BN and graphite with the additions. Hot-pressed SiC-BN composites are therefore promising as self-lubricating, high-performance ceramics, and should be mechanically tested.The microstructure of the sample containing the highest amount of boron nitride showed signs of exaggerated grain growth upon reaching the sintering temperature, with subsequent recrystallization. A boron-carbon exchange mechanism between SiC and BN is proposed, based on BNCx-regions detected in Si-B-C-N polymers. The mechanism is believed to assist vacancy formation in SiC, increasing the sinterability of SiC-BN composites. GDOES measurements and XRD scans support the existence of BNCx regions in the samples with 5 and 10 wt% BN.