Diffusion of chromium and aluminum in Ni-20Cr and TDNiCr (Ni-20Cr-2ThO₂)

Abstract

Diffusion coefficients have been measured for⁵¹Cr in fine- and coarse-grained TDNiCr (Ni-20Cr-2ThO₂) and in fine-grained Ni-20Cr in the temperature range of 1038° to 1200°C. Selective diffusivities have also been determined for specimens of these alloys which were aluminized to give an initial surface concentration of 5.8 wt pct Al. Finally, diffusion coefficients for interdiffusion of aluminum in TDNiCr and Ni-20Cr have been obtained from electron probe microanalysis of the aluminized specimens. For a given grain size and temperature there is no difference in diffusivities for chromium diffusion in TDNiCr or Ni-20Cr. Diffusion coefficients increase with decreasing grain size for both alloys. Comparison of aluminum diffusion data obtained from electron microprobe profiles with radiotracer chromium diffusivities suggests that aluminum diffuses approximately three times faster than chromium in TDNiCr and Ni-20Cr.