Effect of Stress on Mobilities

Consider again the diffusion of small interstitial atoms among the interstices between large host atoms in an isothermal unstressed crystal as in Section 3.1.4. According to Eqs. 3.35 and 3.42, the flux is given by 

The diffusion is isotropic and the mobility, M, is a scalar, as assumed previously. 

16When the stress is nonuniform and stress gradients exist, the stress will exert a force, as discussed in the following section. 

17The tensor nature of the diffusivity (mobility) in anisotropic materials is discussed in Section 4.5. 

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