The migration of Ni in martensites with 0 to 30wt%Ni was studied between 300 and 700C by using electron microprobe techniques. Homogeneous austenite samples were quenched in order to obtain martensite. The diffusion coefficients were found by comparing the measured concentration profiles with those calculated from simulations. At temperatures greater than 410C, the diffusivities (table 141) could be described by:

D (cm2/s) = 4.25 x 10-3 exp[-49.0(kcal/mol)/RT]

At temperatures below 410C, the diffusivity was described by:

D (cm2/s) = 2.27 x 10-15 exp[-10.60(kcal/mol)/RT]

The discontinuous nature of the Ni diffusion in these martensites was attributed to a high dislocation density. Thus, at temperatures greater than 410C, lattice diffusion was deduced to be the predominant mechanism. At temperatures below 410C, dislocation pipe diffusion predominated.

A.D.Romig, J.I.Goldstein: Metallurgical Transactions A, 1981, 12[2], 243-9