Evaluation of reaction barrier compensating coatings on SCS-6 fibers in Ti-24Al-11Nb(at%) composites

Abstract

The objective of the present study is to determine the influence of surface coatings prepared by sol-gel techniques on microstructure and residual stress distribution in SCS-6/Ti-24AI-11Nb composites. The approach taken was to apply two different oxide coatings with varying thermal expansion coefficients and elastic moduli to the surface of the SCS-6 fibers. Yttrium oxide and magnesium oxide were chosen since each were reportedly compatible with titanium matrices. Layers of two different thicknesses (approximately 0.1 μm and 0.5 μm for the magnesia and 0.5μm and 1.0 μm for the yttria) were applied to the fibers for comparison. The fibers were then placed in the matrix foil and vacuum hot pressed to final consolidation. The integrity of the various coatings, their stability with respect to the fiber and matrix, how they influence the β-depleted region, and their effect on residual stresses, matrix cracking and interfacial strength was studied after exposure to elevated temperatures for different periods of time.