Interdiffusion in Co–Pd Alloys

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Abstract
Interdiffusion in Co–Pd alloys has been studied in the temperature range between 880 and 1193°C, using diffusion couples of pure cobalt and pure palladium. Balluffi’s method has been employed to determine the interdiffusion coefficient, \ ildeD, as a function of concentration. It has been found that the value of \ ildeD increases as the melting temperature of this binary system decreases and shows a maximum at the composition about 62 at% Pd. From the Arrhenius relationship, the activation energy \ ildeQ and the frequency factor \ ildeD0 for interdiffusion have been calculated for each concentration. The influence of the magnetic transformation on interdiffusion is clearly detected. In the alloys containing 10 and 20 at% Pd, Δ\ ildeQ=\ ildeQ(ferromagnetic region)−\ ildeQ(paramagnetic region) has been shown to be 2.5 and 0.3 kcal/mol, respectively. Using the thermodynamic data by Bidwell et al., the thermodynamic factor in Darken’s equation has been calculated, and the contribution of it to the apparent activation energy above and below the Curie temperature has heen estimated. Further, it has been shown that the influence of the magnetic transformation on the activation energy for interdiffusion is smaller than that for self-diffusion. Movement of the Kirkendall markers toward the cobalt side and formation of voids on the cobalt side have been detected. The calculated values of the intrinsic diffusion coefficients at the marker composition (22.5 at% Pd) show that cobalt atoms diffuse much faster than palladium atoms in this alloy.

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