Coble Creep, Involving Grain-Boundary Diffusion

5 Coble Creep, Involving Grain-Boundary Diffusion 

For steady-state creep, where Fick s law applies, the flux at the 60° boundary is  

Other expressions are given for Coble s creep, the difference being in the coefficient representing the assumptions in each case (in Coble and Guerard [37] it 

by writing the coefficient as a constant, the common expression is  

The subscripts refer to the grain boundaries, Q is the atomic volume (of a vacancy), S is the grain-boundary width and 1 is the grain size. (In Nabarro-Herring, grain size was denoted by d). The Ds in Eqs. (6.47) and (6.48) is replaced, in Coble s equation, by Dgb. Factor 1/1 represents the density of the cross-section 

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