Diffusion in Metals, Intermetallics, Silicides, Quasicrystals and Metallic Glasses
Diffusion in Ni-Mn and Ni-Pt Alloys
Nickel-manganese and platinum-manganese alloys are of technological interest due to their antiferromagnetic
properties and due to their applications in thin-film GMR storage devices. Their diffusion behaviour was
completely unknown, when we started this project. So far self-diffusion of nickel and manganese has been
investigated by the radiotracer technique in Ni50Mn50 alloys over a wide
temperature range. Experiments were performed on disordered fcc, B2 and L10 structure phases
of the equiatomic alloy at high, intermediate, and low temperatures, respectively. The diffusivity of
manganese was found to be significantly faster (factor 3 to 5) than that of nickel in the fcc and
B2 phases. More than one order of magnitude diffusivity increase was observed upon the transition from
the higher temperature fcc to the intermediate temperature B2 phase. The activation enthalpy of nickel
self-diffusion in the disordered fcc phase is higher than the corresponding value for manganese. In the
B2 phase there is only a slight difference between the activation enthalpies of the components, which
indicates a coupled diffusion mechanism of the two components. A comparison of the present tracer
self-diffusion data with literature data on interdiffusion in the Ni-Mn system permits to estimate thermodynamic
factors by using the Darken-Manning equation. The thermodynamic factor varies from 3 to 5 depending
onthe structure.
