Determination of residual stresses in thin sheet titanium aluminide composites

Abstract

Residual stresses in Ti3Al/SiC composites have been measured using two methods. The compressive residual stresses in the fibers were inferred from measurements of the change in their length when the matrix was entirely removed by etching. The stresses were found to vary substantially from fiber to fiber. The longitudinal and transverse stresses in the matrix were measured by X-ray diffraction. Repeated measurements were made as the outer layer of alloy was removed by electropolishing as far as the first row of fibers. In one composite of lower fiber volume fraction, the matrix stresses were thus found to be approximately uniform throughout the specimen. In a higher volume fraction material, on the other hand, the matrix stresses increased significantly with depth from the outer surface: the longitudinal matrix stresses among the fibers were found to be about 60 pct larger than they were on the specimen surface. The implications of these measurements for processing and reliability of thin sheet titanium aluminide composites are discussed.