A study of the reaction zone in an SiC fiber-reinforced titanium alloy composite

Results on several aspects of a SiC fiber-reinforced IMI-829 (α-titanium alloy) metal matrix composite (MMC) are presented. Scanning Auger microscopy (SAM) of SiC fibers reveals a high concentration of oxygen which varies across the diameter of the fibers. It also shows that composition of SiC changes across the diameter and, for the most part, is carbon-rich nonstoichiometric SiC. Transmission electron microscopy (TEM) of thin MMC foils shows the presence of TiC and TiSi₂ in the reaction zone. Postfabrication thermal exposures of MMC s at 975 °C lead to void formation in the reaction zone. Concentration profiles of various elements across the reaction zone reveal a buildup of Zr, Nb, and Si and a decrease of Ti, Al, and Sn in the matrix around the reaction zone. Void formation in the reaction zone has been explained by the relatively high flow of Si atoms to the matrix leading to an accumulation of vacancies in the reaction zone which condense to form voids. In addition, an enhancement of hardness in the matrix around the reaction zone has been attributed to a strengthening of the matrix by solid solution and precipitation hardening, together with a contribution from residual stresses. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee.