Diffusion processes at the MnSi1.75/Cr contact

Diffusion processes between chromium and the higher manganese silicide MnSi1.75 in MnSi1.75/Cr and MnSi1.75/Cr/Ni contact regions are studied by microstructural analysis and x-ray microanalysis. The results demonstrate that, at elevated temperatures, the composition and sequence of layers in the diffusion zone between MnSi1.75 and Cr are consistent with the phase equilibria in the Cr-Mn-Si system. In MnSi1.75/Cr/Ni samples, a larger portion of the diffusion zone between MnSi1.75 and Cr consists of several Mn-Ni-Si phases and only one Cr-Mn-Si phase. The intermetallic phases forming in the diffusion zones exhibit metallic conduction and high thermal conductivity, which makes it possible to reduce energy losses in the hot Junctions of thermoelements at the interface between an MnSi1.75-based thermoelectric material and metal. It is shown that the use of chromium as a diffusion-impervious layer in MnSi1.75/Cr/Ni contacts not only slows down Ni diffusion in MnSi1.75 but also improves the mechanical properties of the contact.