AN EXPERIMENTAL-STUDY OF RESIDUAL-STRESSES IN SIC-FIBER-REINFORCED TI-BASED COMPOSITES

Composites of two Ti-based alloys (Ti-14Al-21Nb and Ti-6Al-4V (weight per cent)) containing SCS-6 SiC fibers have been characterized microst ructurally and are used as model systems in which to study the influen ce of fiber volume fraction and post-consolidation deformation on resi dual axial fiber strains. The magnitude and extent of local chemical s trengthening of the matrix due to interstitial C diffusion have also b een measured. A novel matrix etching technique was used to measure the axial fiber residual stress in the composites, and analysis of electr on backscattered channeling patterns was employed as a qualitative mea ns of measuring the extent of the local plastic yielding in the matrix . The measured fiber residual strain was found to depend on fiber volu me fraction and was reduced significantly by the application of a mech anical load in excess of the matrix yield stress. Significant fiber-to -fiber variation in axial residual strain is measured in the (Ti-14Al- 21Nb)-SiC composite, and this variation is discussed with respect to c ontributions from variations in local fiber volume fractions (i.e. fib er spacing), matrix plasticity, and fiber bending resulting from the c ross-weave process. In general, measurements of elastic residual fiber strains are in good agreement with analytical model predictions.