Measurements of bulk-to-surface segregation of impurities in electrodeposited NiCr alloys by auger electron spectroscopy

Auger Electron Spectroscopy (AES) measurements of the non-equilibrium segregation of K to the surface of an electrodeposited NiCr alloy of 20%Ni-80%Cr composition are reported. It is shown that a surface enrichment of K takes place on the surface to a maximum of 8% coverage in the temperature range 400–550°C. The process is initially diffusion-connrolled, with an activation energy of 17 ± 3 kJ/mol. An electrodeposited alloy of approximately 80%Ni-20%Cr composition showed a considerable C-enrichment at the surface in the temperature range 300 to 600°C. A cast alloy of the same composition showed a similar C-enrichment in the temperature range 300 to 455°C. The electrodeposited alloy of 20%Ni-80%Cr showed no such C-enrichment, due to the segregation of both K and Cr to the surface in the range 300 to 600°C and the formation of chromium carbide precipitates.