High temperature reaction zone growth in tungsten fiber reinforced superalloy composites: Part I. Application of the moving boundary equations

The nature, kinetics, and rate-controlling process for high temperature reaction zone growth in tungsten fiber reinforced superalloy (TFRS) composites are determined. The matrix alloys considered in this study are INCOLOY 903 and a W-modified INCOLOY 903. The kinetics and rate-controlling process for reaction zone growth are determined by direct application of the moving boundary equations. The results show that reaction zone growth is a results of longrange interdiffusion and that the rate-controlling process for reaction zone growth is interdiffusion across the reaction zone. Further, the results show that the interdiffusion coefficients of the reaction zone can be calculated from the parabolic rate constants for the reaction zone growth without directly considering the kinetics of diffusion in the matrix. The activation energy,Q, and the frequency factor,D _o, for the interdiffusion across the reaction zone in the INCOLOY 903 matrix composite are experimentally determined to be 268 kJ/mole and 0.22 cm²/s, respectively. Further, the relative chemical stability of the reaction zone is discussed with respect to reaction zone chemistry. T. CAULFIELD, formerly Postdoctoral Research Scientist at Columbia University, is Senior Member of Research Staff, Philips Laboratories, Briarcliff Manor, NY 10510. J. K. TIEN is Henry Marion Howe Professor and Director, Center for Strategic Materials, Henry Krumb School of Mines, Columbia University, New York, NY 10027.