The bulk diffusion coefficients were determined by using the serial sectioning technique and 64Cu tracer at 1070 to 1570K. Grain boundary diffusion was studied at 700 to 1100K. It was found that the bulk diffusivities (table 189) could be described by:

D(m2/s) = 0.000288 exp[-270.8(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 (table 190) could be described by:

D(m2/s) = 0.000113 exp[-165.8(kJ/mol)/RT]

Autoradiographic methods were also used to study segregation of the tracers. 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

Table 181

Bulk Diffusivity of 51Cr in Ni-16.49Cr-7.40Fe-0.015wt%C