Status of, and prospects for, the development of titanium metal-matrix composites

Increasing demands for high performance structural components have driven existing materials to the limits of their performance. Materials with higher strength, stiffness, adequate fatigue and fracture resistance and high temperature capabilities are needed to meet the challenge. Titanium alloys offers considerable scope in certain critical demand areas. Although the new high temperature titanium alloys -- IM1829 and IM1834 -- have been developed with broad property capabilities up to 650 degree C, they lack the microstructural, environmental and thermal stability required to withstand prolonged exposure at this temperature. The further development of Ti-alloys capable of operating up to 900 degree C has focused attention on the possible exploitation of Ti based metal-matrix composites (MMCs) utilizing SiC fibers. Thus, the development of fiber technology has been slow; the choice of suitable high temperature Ti-alloy matrices is still limited; but, most significantly, undesirable fiber/matrix interfacial interaction may be promoted by the materials' inherent non-equilibrium state under these demanding conditions. Preliminary experimental diffusional studies relating to Ti, TiN and FeCr alloy-coated SiC fibers intended for use within Ti-alloy MMC's, and kinetic data concerning the high temperature oxidation/sulfidation behavior of TiN diffusion barrier layers obtained by the Ion Bond technique are described. SIMS data indicated a considerably greater degree of interdiffusion in the cases of Ti and FeCr alloy-coated SiC fibers in comparison with the TiN/SiC system. Corrosion studies of TiN-coated Co20Cr and Mo substrates in air and S2/O2 (pS210-1Pa/pO210-1 Pa) environments at 500--1000 degree C revealed the generally beneficial effects of the TiN cover relative to the Co20Cr and Mo control samples