Effects of microstructure on the strength and fatigue behavior of a silicon carbide fiber-reinforced titanium matrix com
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I.
INTRODUCTION
THE strong interest in the development of improved transonic and hypersonic aerospace vehicles has stimulated considerable research on the development of light weight, high temperature materials, with the potential to replace existing nickel- and titanium-base alloys.[1,2] Some of this effort has led to the identification of fiber-reinforced titanium matrix composites as candidate materials for applications in the intermediate temperature regime between 500 7C and 6507C. Titanium matrix composites (TMCs) have been considered mainly as a result of their attractive combinations of high temperature strength and stiffness, as well as their creep resistance in the potential service temperature regime. Unfortunately, however, fiber-reinforced TMCs have been shown to have only limited fatigue[3–14] and fracture[15,16,17] resistance. Also, many of the TMCs have inherently anisotropic properties and worse mechanical properties than their matrix alloys, especially in the transverse orientation. This is in spite of the significant levels of crack-tip shielding that have been shown to occur in W.O. SOBOYEJO, Associate Professor, and Y. LI, Postdoctoral Research Fellow, Department of Materials Science and Engineering, and S.I. ROKHLIN, Professor, Department of Industrial, Welding and Systems Engineering, The Ohio State University, Columbus, OH 43210-1179. B.M. RABEEH, formerly Graduate Research Assistant, Department of Materials Science and Engineering, The Ohio State University, is Department Head, The Military Technical College, Cairo, Egypt. Y.C. CHU, formerly Graduate Research Associate, Department of Industrial, Welding and Systems Engineering, is Research Engineer, Philips Taiwan Division, Taipei, Taiwan, People’s Republic of China. A. LAVRENTENYEV, formerly Graduate Research Associate, Department of Industrial, Welding and Systems Engineering, The Ohio State University, is Scientist, United Technologies Research Center, East Hartford, CT 06108. Manuscript submitted November 1, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
TMCs.[12,13] There is, therefore, a need for an improvement in the basic understanding of failure mechanisms in TMCs. Previous studies conducted on TMCs with various architectures have revealed that a complex sequence of damage is associated with failure under monotonic[15,16,17] and cyclic[13,14] loading. In particular, recent high resolution transmission electron microscopy studies[18,19] have shown that the layered interfacial microstructure that exists between the fiber and the matrix has a highly complex structure. This layered interface, which consists predominantly of titanium carbides (TiC and Ti2C), has also been shown to promote early nucleation of fatigue damage at the fiber/matrix interface.[14] Furthermore, although many of the TMC systems under consideration have metastable beta titanium matrices that may undergo phase transformations in the anticipated service temperature regime, the effects of microstructure on the mechanical properties of TMCs are not fully underst
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