Effect of fiber spacing on interfacial damage in a metal matrix composite

The nature and the location of cracking in a Ti-V-Cr-Al-Sn/SiC composite (Ti-15V-3Cr-3Al-3Sn, in wt pct, reinforced by 33 vol pct of continuous unidirectional SCS-6SiC fibers) before and after unconstrained thermal cycling were investigated. The material was subjected to 10,000 thermal cycles between 300 and 550 C and samples were examined for cracks in the fiber, the matrix, and the fiber-matrix interface, using a back-scattered SEM. The Ti-based metal matrix composite was found to have a substantial amount of interfacial damage in the form of radial cracks, which formed first in the C-rich coating of the SiC fiber and then in the fiber-matrix reaction zone. The cracking was related to the fiber distribution, with consistently more cracking found between the more closely-spaced fibers within a given row, and more radial cracking in the outside fiber rows.