High temperature reaction zone growth in tungsten fiber reinforced superalloy composites: Part II. Matrix chemistry effe
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I. I N T R O D U C T I O N
IN Part
I of this work, the use of the moving boundary equations, coupled with the interdiffusional experiments and phase equilibrium rationalization, showed that reaction zone growth in Tungsten Fiber Reinforced Superalloy composites is rate-controlled by interdiffusion across the reaction zone. Further, the composition of the reaction zone phase was related to the stability of the intermetallic phases that form in the Co-W, Fe-W, and Ni-W binary systems. It was suggested that Co and Fe form a more stable reaction zone phase than does Ni in TFRS composites. In this paper, the kinetics of reaction zone growth are correlated to matrix chemistry by experimentally determining the interdiffusion coefficients of the reaction zone phase for various metal matrix/W-fiber composites. The matrix chemistries were chosen with various amounts of Co, Fe, and Ni present, such that reaction zone phase stability discussed in Part I could be related to reaction zone kinetics.
II. E X P E R I M E N T A L P R O C E D U R E AND RESULTS The various metal matrix/W-fiber composites examined in this work have matrix components consisting of stainless steel 316, Fe-Cr-AI-Y, INCOLOY* 907, I N C O L O Y 903, and W A S P A L O Y . * Table I is a listing *INCOLOY is a trademark of the INCO family of companies. *WASPALOY Corporation.
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of the chemistries of each matrix studied. The composite
J.K. TIEN is Henry Marion Howe Professor of Materials Science and Director at the Center for Strategic Materials, Henry Krumb School of Mines, Columbia University, New York, NY 10027. T. CAULFIELD, formerly Postdoctoral Research Scientist at Columbia University, is a Senior M e m b e r of Research Staff at Philips Laboratories, Briarcliff Manor, NY 10510. Y.P. W U is a Graduate Research Assistant at the Center for Strategic Materials, Columbia University, New York, NY 10027. Manuscript submitted November 6, 1987. METALLURGICAl. TRANSACTIONS A
geometry of these metal matrix/W-fiber systems is similar to that of I N C O L O Y 903 and W-modified 903 TFRS composites discussed in Part 1. The only difference is that the initial fiber spacing of these composites is approximately 200 /xm, twice that of the I N C O L O Y 903 and W-modified I N C O L O Y 903 composites. Figure 1 contains photomicrographs of representative crosssections of the as-received metal matrix/W-fiber composites. The photomicrographs reveal that, for certain matrix compositions, a substantial reaction zone exists. This initial reaction zone is a result of the thermal exposure associated with composite fabrication. The metal matrix composites were vacuum annealed at 1093 ~ for various times ranging from 10 to 100 hours. The as-annealed composites were sectioned, mounted, and metallographically prepared for optical and SEM analysis. The reaction zone boundaries were measured for each annealing time (see Part I for additional experimental details). Figure 2 contains photomicrographs of cross-sections of the various meta
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