Bulk diffusion of 57Co in polycrystalline gold near the lower homologous temperature of traditional investigations of bulk diffusion in polycrystals : Two components of the bulk diffusion flux in the 57Co(Au) system

Diffusion of 57 Co in polycrystalline gold was investigated at temperatures of 966 and 873 K by two methods. Atomic-probe diffusion profiles were obtained by the traditional layer-by-layer method (division of the diffusion zone into layers and measuring layer concentrations using a single-channel spectrometer equipped with a scintillation detector with a well). The intensities of two components of 57 Co radiation were also measured in the remainder of the sample (using a spectrometer with a HPGe detector with high resolution in energy) after the removal of layers of various thicknesses. The profiles obtained consist of three parts: two parts are primarily due to bulk diffusion with two different diffusion coefficients, and one part is mainly due to grain-boundary diffusion. The slow component of bulk diffusion in this system is due to atomic probes in the paramagnetic state. The enthalpy of activation for slow diffusion of 57 Co in gold (Q bulk ) p = 236 kJ/mol agrees with the parabolic charge dependence of the difference Q 21 between the enthalpies of activation for bulk diffusion of impurity (Q 2 ) and host (Q 1 ) atomic probes. The fast component of bulk diffusion in this system is due to 57 Co atomic probes in the ferromagnetic state. The magnetic moments of the 57 Co atomic probes that contribute to the fast component of the flux of bulk diffusion become stabilized by the vacancy enhancement of the local magnetic moment of cobalt atoms, which form vacancy-residual impurity iron complexes during diffusion.