Experimental evidence for anomalous grain boundary diffusion of Fe in Cu and Cu-Fe alloys

Abstract Fe grain boundary diffusion is measured in 99.995 wt.% pure Cu and the Cu-Fe alloys with iron contents of 0.18, 0.45, 0.6 and 0.8 wt. % using the radiotracer technique and applying the 59Fe isotope. A series of isothermal experiments at 1000 K reveal that the triple product of iron grain boundary diffusion is almost independent on the iron content excepting the alloy containing 0.8 wt. % of Fe where the triple product is increased by three orders of magnitude. Additional experiments at 1100, 900 and 717 K using this alloy confirm the anomaly observed at 1000 K, namely the triple product is continuously increasing following the Arrhenius dependence from 717 to 1100 K except the temperature of 1000 K, where the triple product is anomalously high. The observed experimental results are explained by the analysis of thermodynamic equilibrium and solubility of Fe and S in Cu.