A Mossbauer study of local atomic order in AuFe alloys

Abstract

The first atomic order parameter, alpha 1, has been determined for a series of Au100-xFex alloys (x=5, 10, 15 and 20) from an analysis of room-temperature Mossbauer spectra. All alloys in the as-rolled state exhibit positive values of alpha 1, indicative of clustering of Fe atoms within the Au matrix. Changes in atomic order are introduced with heat treatment. At low annealing temperatures, negligible change is observed in the values of alpha 1, due to the slow diffusion rates, but with increasing aging temperature the value of alpha 1 decreases and finally becomes negative, indicative of atomic short-range order. The lack of change of alpha 1 with heat treatment at aging temperatures greater than about 200 degrees C and about 330 degrees C, respectively, in Au95Fe5 and Au90Fe10 is due to the limitation imposed by the quench time with substantial reordering occurring during the quench. The metallurgical state of AuFe alloys annealed at high temperatures is therefore primarily dependent on the quench time. The diffusion process in AuFe alloys is shown to be predominantly via a single-vacancy diffusion mechanism.