Abstract
Reaction is caused at the interface between fiber and metal-matrix in a composite at an elevated temperature. The reaction affects greatly on the strength of the composite. In this work, SiC fiber reinforced Ti alloy composites were fabricated by diffusion bonding. The reaction products were examined after heat-treatment of the composites. Effect of the reaction products on the strength of the composites was studied.
SiC fiber was used as the reinforcement material. Ti, Ti-6A-4V or Ti-8Mo/Ti-6A-4V was used as the matrix. The heat-treatment was carried out at a temperature 1073 or 1123 K for 32.4-360 ks. The strengths of heat-treated composites were measured at a room temperature.
In the case of Ti matrix, the strength of composites decreased to 60% with increasing temperature and time of the heat-treatment. The decreasing of the strength of composites was little in the cases of the alloy matrices except at 1123 K for 360 ks.
The reaction products were TiC and Ti5Si3 in every matrices of this work. TiC was formed on the surface of the SiC fiber and Ti5Si3 was formed outer for TiC.
From these results, the alloying elements were effective to decrease the reaction at the interface. The abrupt decrease of the strength of the composites was due to increasing of defects between SiC and the reaction products.
A small pit was often observed at the periphery of the fiber in fracture surface. The morphology of the fracture surface showed the pit was the initiation of the crack propagation. This means the deterioration of the fiber depends not on the thickness of the reaction zone but on the pit, especially in the case of serious degradation. Then the deterioration of the fiber was often rather serious even though the thickness of the reaction zone was small.
