Abstract
In this study, pressureless sintering of silicon nitride via the addition of chromium oxide was investigated. Silicon nitride samples containing additives from the Cr–Cr2O3–SiO2 system were sintered under different conditions. The phase transformation, the degree of densification and the in situ reactions between Si3N4 and chromium compounds were investigated and the reactions were validated thermodynamically. It was found that Si3N4 reacts with Cr2O3 and Cr and these in situ reactions lead to Si3N4 decomposition and consequently formation of a series of chromium silicides including Cr3Si, Cr5Si, and CrSi2. Due to the presence of chromium silicides as liquid phases during sintering, the α‐Si3N4 to β‐Si3N4 phase transformation started around 1400°C and was completed around 1800°C. On the other hand, densification of Si3N4 samples with chromium oxide addition was not observed. The participation of Cr2O3 in these in situ reactions prevents sufficient formation of chromium silicate and leads to insufficient liquid phase with poor wettability during sintering, resulting in poor densification.
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