Interdiffusion in Co-Mn alloys

Abstract

Interdiffusion coefficient\(\tilde D\) in cobalt-manganese alloys has been determined by Matano's method in the temperature range between 1133 and 1423 K on (pure Co)-(Co-30.28 at. pct Mn alloy) and (pure Co)-(Co-51.76 at. pct Mn alloy) couples. This, ∼D, has been found to increase with the increase of manganese content. However, the activation energy (∼Q) and frequency factor (\(\tilde D\)0) show a maximum at about 10 at. pct Mn. The concentration dependence of\(\tilde D\) and\(\tilde Q\) has been discussed taking into account the thermodynamic properties of the alloy. The difference in\(\tilde Q\) between the ferro- and paramagnetic phases in Co-5 at. pct Mn alloy has been found to be 24 kJ/mol, which is larger, than that for the diffusion of Mn54 in this alloy. Further it has been found that the Kirkendall marker moves toward manganese-rich side, showing that manganese atoms diffuse faster than cobalt atoms. From the marker shift, the intrinsic diffusion coefficients,DCo andDMn, at 33 at. pct Mn have been determined as follows:DCo=0.22×10−4 exp(−263 kJ mol−1/RT) m2/s, andDMn=0.98×10−4 exp(−229 kJ mol−1/RT) m2/s.