Diffusion studies in the beta (B-2), beta ' (Bcc), and gamma (Fcc) Fe-Ni-Al alloys at 1000 degrees C
Abbreviated Journal Title
Metall. Mater. Trans. A-Phys. Metall. Mater. Sci.
ZERO-FLUX PLANES; INTERDIFFUSION COEFFICIENTS; MULTIPHASE DIFFUSION; MULTICOMPONENT DIFFUSION; TERNARY DIFFUSION; COUPLES; SYSTEM; REVERSALS; INTERFACE; PHASE; Materials Science, Multidisciplinary; Metallurgy & Metallurgical; Engineering
Diffusion studies were carried out in the Fe-Ni-Al system at 1000 degreesC with solid-solid diffusion couples assembled with beta (beta(2)), beta' (bcc), and gamma (fcc) single-phase alloys for the development of diffusion structures, diffusion paths, and for the determination of interdiffusion and intrinsic diffusion coefficients. The diffusion structures were examined by optical and scanning electron microscopy, and the concentration profiles were determined by electron microprobe analysis. Diffusion couples included several series of beta vs gamma and beta' vs gamma diffusion couples characterized by a common terminal alloy bonded to several terminal alloys with varying compositions. The development of planar and nonplanar interfaces, as well as two-phase layers, as observed in various couples, were related to the diffusion paths. The interdiffusion fluxes of individual components were calculated directly from the experimental concentration profiles, and the diffusional interactions among components were examined in the light of zero-flux planes (ZFPs) and flux reversals, which were identified in several couples. Ternary interdiffusion coefficients ((F) over tilde (Fe)(i,j) (i, j = Al, Ni)), with Fe considered as the dependent concentration variable, were evaluated at composition points of the intersection of diffusion paths. of single-phase couples and of multiphase couples that developed planar interfaces. The interdiffusion coefficients were the largest in magnitude for the beta' alloys, especially near the beta/beta' miscibility gap, and decreased for the beta and gamma alloys. In the beta and gamma phases, the main interdiffusion coefficient for Al was larger than those for Ni and Fe. Also, Fe interdiffused faster than Ni in the Fe-rich beta and beta' phases. The cross-interdiffusion coefficients ((D) over tilde (Fe)(AlNi) and (D) over tilde NiAlFe) were negative in all three phases. In general, the (D) over tilde (Fe)(AlNi) coefficients were larger in magnitude than the (D) over tilde (Fe)(NiAl) coefficients; however, the magnitude of (D) over tilde (Fe)(NiAl) was greater than that of (D) over tilde (Fe)(AlNi) near the beta/(beta + gamma) phase boundary on the ternary isotherm. In the beta phase, the magnitude of (D) over tilde (Fe)(ij) (i, j = Al, Ni) coefficients increased over 1 to 2 orders of magnitude with a decrease in the Al concentration and increase in the Fe/Ni concentration ratio. Interdiffusion coefficients, extrapolated from the ternary coefficients for binary alloys, were consistent with those in literature. Intrinsic diffusion coefficients were also determined at selected compositions. In addition, tracer diffusion coefficients were estimated for the binary Fe-Al and Ni-Al alloys at selected compositions, from an extrapolation of ternary interdiffusion coefficients.
Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
"Diffusion studies in the beta (B-2), beta ' (Bcc), and gamma (Fcc) Fe-Ni-Al alloys at 1000 degrees C" (2002). Faculty Bibliography 2000s. 3482.