Fabrication and properties of Si−Hf alloy melt-infiltrated Tyranno ZMI fiber/SiC-based matrix composites

The fabrication of Tyranno ZMI fiber/SiC-based matrix composites by a melt infiltration (MI) process using Si−8.5 at%Hf alloy was investigated. The Si−Hf alloy was utilized instead of pure Si for MI processing in order to lower the MI temperature to below 1400 °C as well as to inhibit the thermal degradation of amorphous SiC fibers. Microstructural characterization revealed that the composite fabricated by Si−8.5 at%Hf alloy MI at 1375 °C had a highly dense matrix comprising reaction-formed SiC and unreacted Si−HfSi2 phases. The Si−Hf alloy melt-infiltrated composite exhibited approximately 35% higher bending strength than a conventional Si melt-infiltrated composite fabricated at 1450 °C. Further, it was confirmed that Si−Hf alloy melt-infiltrated composite maintained its strength up to 1200 °C in an Ar atmosphere. These results clearly demonstrated that the Si−8.5 at%Hf alloy offers sufficient infiltration ability and reactivity to form a dense SiC-based matrix at 1375 °C.