The bulk diffusion coefficients were determined by using the serial sectioning technique and 60Co tracer at 1070 to 1570K. Grain boundary diffusion was studied at 700 to 1100K. It was found that the bulk diffusivities could be described by:

D(m2/s) = 0.000309 exp[-260.1(kJ/mol)/RT]

The grain boundary diffusivities were deduced by using the Whipple or Suzuoka method. Both techniques gave similar values. The grain boundary diffusion data could be described by:

D(m2/s) = 0.0000324 exp[-151.0(kJ/mol)/RT]

Autoradiographic methods were also used to study segregation of the tracer. It was found that, in the case of small-grained (0.2mm) specimens at above about 1000K, both volume and grain boundary diffusion processes contributed to the penetration of tracer atoms into the bulk. At temperatures below 960K, migration occurred mainly via the grain boundaries.

A.R.Paul, M.C.Naik, K.S.Venkateswarlu: Journal of Nuclear Materials, 1987, 149, 277-82