Interdiffusion in Co–Pt Alloys

Abstract

Interdiffusion coefficients (\ ildeD) in cobalt-platinum alloys have been determined by Matano’s method in the temperature range between 1271 and 1673 K using couples of pure cobalt and platinum. It was found that at all temperatures, \ ildeD increases with platinum content up to about 40 at% and decreases gradually with a further increase of platinum. However, both the activation energy (\ ildeQ) and the frequency factor (\ ildeD₀) have a maximum value at about 10 at%Pt. The logarithm of the ratio of the interdiffusion coefficient at the melting temperature to the thermodynamic factor for interdiffusion, ln(\ ildeD_Tm⁄m), has been found to be proportional to the concentration of platinum. This relationship is found to be valid for other cobalt alloy as well as nickel alloy systems. The shift of Kirkendall markers toward the cobalt-rich side and the formation of voids in the diffusion zone corresponding to the concentration range of 5 to 10 at%Pt have been observed. From the interdiffusion coefficient and the velocity of markers, the following equations have been obtained for the intrinsic diffusion coefficients, D_Co and D_Pt, in Co–21 at%Pt alloy:
D_Co=2.25×10⁻⁴exp(−278kJ mol⁻¹⁄RT)m²⁄s
and
D_Pt=8.09×10⁻⁴exp(−291kJ mol⁻¹⁄RT)m²⁄s.