Role of boron on the Spark Plasma Sintering of an α-SiC powder

This study deals with the role of non-oxide sintering aids such as boron carbide (B4C) or – free boron (B) plus free carbon (C) – on the Spark Plasma Sintering treatment of silicon carbide. The results so obtained clearly show that free boron plus free carbon additions lead to the higher densification rates. This favourable behaviour with regards to the densification kinetics is accompanied by the absence of any abnormal grain growth. At the opposite, boron carbide additions do not significantly raise the densification kinetic after SPS treatment of SiC in comparison to pure silicon carbide. In this case, TEM investigations point out the formation of a borosilicate vitreous phase due to the dissolution process of B4C in contact with a native superficial silica layer surrounding the SiC grains. The resulting liquid phase leads to an abnormal grain growth coupled with undensifying process.