Micro-alloying effects of yttrium on the microstructure and strength of silicon carbide joint brazed with chromium-silicon eutectic alloy

With the purpose of increasing the joint strength by refining the grain size of CrSi2 and increasing the fraction of Si-CrSi2 eutectic, the authors studied the effect of yttrium (Y) on the microstructure and mechanical property of SiC joints brazed with Si-29 wt% Cr eutectic alloy with varying Y contents (0-1.0 wt% Y). It was found that adding of appropriate content of Y (<0.1 wt%) could refine the grain size of CrSi2 phase and increase the fraction of eutectic region. However, excess addition of 0.5 or 1.0 wt% Y caused the coarsening of CrSi2 phase with the formation of irregular shape Y-Si-rich silicide. The SiC joint brazed with alloy added with 0.1 wt% Y exhibited high shear strength, which was improved approximately 20% in comparison with that without Y. Both the fine size of CrSi2 phase and high fraction of Si-CrSi2 eutectic contributed to the high strength of SiC joint. Interface between the SiC and brazing alloy exhibited a good chemical adhesion without detectable interdiffusion or the formation of reaction phases.