Interdiffusion in Low-Al Fe–Cr–Al Alloys at 1000 °C

Abstract

Interdiffusion coefficients in low-Al Fe–Cr–Al alloys at 1000 °C were experimentally determined by using a diffusion-couple method, and the effects of Cr on the interdiffusion flux of Al were evaluated. The main-term interdiffusion coefficients, ${\widetilde{D}}_{\text{AlAl}}^{\text{Fe}}$ and ${\widetilde{D}}_{\text{CrCr}}^{\text{Fe}}$, decreased with increasing Cr content, and the ${\widetilde{D}}_{\text{AlAl}}^{\text{Fe}}$ values were two to three times greater than the ${\widetilde{D}}_{\text{CrCr}}^{\text{Fe}}$ values. The cross-term interdiffusion coefficient, ${\widetilde{D}}_{\text{AlCr}}^{\text{Fe}}$, was positive, indicating a positive chemical interaction between Cr and Al in the Fe–Cr–Al alloys. ${\widetilde{D}}_{\text{AlCr}}^{\text{Fe}}$ was one order of magnitude smaller than ${\widetilde{D}}_{\text{AlAl}}^{\text{Fe}}$ and decreased with increasing Cr content. Because of the positive ${\widetilde{D}}_{\text{AlCr}}^{\text{Fe}}$ value, when the concentration gradients of Al and Cr had the same sign, the Al interdiffusion flux was increased by Cr and increased with increasing Cr content due to the steeper Cr concentration gradient.