NI SELF-DIFFUSION IN ALLOYED NI3AL

Volume, grain boundary and phase boundary Ni self-diffusion in Ni3Al-b ased alloys with Cr, Mo, Hf, Ta and with B has been studied over a wid e temperature range (750-1100 degrees C). The sectioning technique fol lowed by autoradiography has been used for determination of the concen tration profiles. The diffusion data obtained prove that in the temper ature range of 750-950 degrees C, intercrystalline boundaries make a d ominant contribution to the overall diffusion flow. Grain boundary dif fusion coefficients are 4-5 orders higher than the volume ones, the ac tivation energy is 25-30% lower. Phase boundary diffusion coefficients are 3-4 orders higher than volume ones, the activation energy is 10%, lower. Increase of the aluminium content results in a decrease of dif fusion permeability of both grain and phase boundaries. Copyright (C) 1996 Elsevier Science Limited