Microstructural characterization of the matrix in the SiC fiber-reinforced Ti-15-3 composite
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ransverse cross section of the as-consolidated composite (gb: grain boundary).
Microstructural Characterization of the Matrix in the SiC Fiber-Reinforced Ti15-3 Composite S.Q. GUO and Y. KAGAWA SiC(SCS-6) fiber-reinforced Ti alloy matrix composites have received special attention because of their high specific stiffness and strength, and they are expected to be used in aerospace structural applications.[1–4] Studies have indicated that the mechanical properties of the composites depend significantly on the properties of fiber, matrix, and interface, which are associated with their microstructures. The microstructures of both the fiber and the interfaces have been studied extensively;[5–12] however, details of the microstructure of the matrix are not yet known. Some studies revealed that a b-depleted matrix zone existed around the fiber,[13] and a volume change occurred in the matrix by phase transformation during heat treatment of the composite.[14] In addition, the interface reaction behavior strongly depended on interdiffusion of both silicon and carbon from the SiC fiber to the matrix and of titanium in the opposite direction.[9–12] These behaviors have considerable effects on the mechanical performance of the composites. Thus, it is important to understand the details of the microstructure of the Ti matrix. The present study is focused on the investigation of the microstructure of the Ti matrix in the SiC(SCS-6) fiber-reinforced Ti-15-3 alloy matrix composite. The SiC(SCS-6), from Textron Co. (Lowell, MA), fiber was '140 mm in diameter continuous b-SiC fiber with an outermost coating layer of '3.6 mm, which reduced the
S.Q. GUO, Postdoctoral Research Fellow, and Y. KAGAWA, Associate Professor, are with the Institute of Industrial Science, The University of Tokyo, Tokyo 106, Japan. Manuscript submitted September 15, 1997. 702—VOLUME 29A, FEBRUARY 1998
Fig. 2—A TEM bright-field micrograph of the Ti-15-3 matrix (a phase: white part; and b 1 v phases: black part).
stress concentration of the SiC fiber.[5,15] The Ti-15-3 alloy is a metastable b-Ti (bcc) stabilized by vanadium.[16] The composite is a six-ply unidirectional SiC(SCS-6) fiber-reinforced Ti-15-3 composite with a thickness of '2 mm, and the composite was fabricated by Mitsubishi Heavy Industries Co., Ltd. (Tokyo) using a foil-fiber-foil consolidation technique. The composite, in which the nominal fiber volume fraction was '0.32, was fabricated by hot isostatic pressing at a temperature of 1153 K under a pressure of 100 MPa for 1.5 hours. Then, the composite was aged in air at 723 K for 16 hours. Chemical analysis of the Ti-15-3 matrix alloy after processing revealed that the chemical composition was 15.22 wt pct V, 3.26 wt pct Cr, 3.12 wt pct Al, 2.94 wt pct Sn, and the remainder Ti. Thin composite specimens were cut from the composite panel using a low-speed diamond saw; the thickness direction was parallel to the fiber axis. The sliced thin specimen was mechanically ground from both sides of the cut surface using a 1-mm diamond paste. Then the foil wa
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