Abstract
Nickel-alumina alloys have been made by powder metallurgy and rolled out to thin sheets. The diffusion rates of 63Ni in these alloys have been measured by the surface decrease method and the enhancement of diffusion has been shown to be due to the grain boundaries. Autoradiography, and microprobe analysis on nickel-alumina/cobalt diffusion couples, have confirmed this view. The diffusion rate for temperatures between 820 and 1220°C can be expressed by the equation: D = 1.8 exp(-65800/RT) exp ((140.9/T-0. 0893)B) where B = grain boundary density (mm-1) At temperatures above 900°C with fine grain sizes the following equation is more suitable. D = 1.8 exp(-65800/RT) + 2.14 x 10-6B exp (-40000/RT) An approximate calculation of the grain boundary diffusion coefficient from the same results yields the following equation: D = 2.14 exp (-40000/RT).