Influence of carbon sources on nitriding process,microstructures and mechanical properties of Si3N4 bonded SiC refractories

The incomplete nitriding and heterogeneity structure of large-size Si₃N₄-bonded SiC refractories limited its application in refractories industry. The objective of this work was to provide a way that adding carbon in matrix with the expectations of carbon could reacted with free-Si and transformed into SiC after nitridation. The effects of carbon sources on the bonded morphologies and nitridation process of Si₃N₄ bonded SiC refractories were investigated. Results indicated the strength and Young’s-modulus of specimen with carbon black increased to 39.4 MPa and 103.89 GPa from 29.8 MPa and 73.43 GPa, respectively. The residual Young’s-modulus also improved from 44.13 GPa to 62.9 GPa after 9-quenching cycles. For specimen with graphite, residual graphite after nitridation resulted in a definite strength decline, but residual strength after quenching was improved. Moreover, analysis results on N-elements indicated surprisingly improvement in the nitriding degree for specimen with carbon black. The microstructure evolution and mechanism associating with the enhanced nitriding process was discussed.