Diffusional Creep of Two-Dimensional Polycrystals

A representative model is a two-dimensional polycrystal composed of equiaxed hexagonal grains. In a dense polycrystal, diffusion is complicated by the necessity 

9 Different growth-law exponents are obtained for other dominant transport mechanisms. Coblenz et al. present corresponding neck-growth laws for the vapor transport, grain-boundary diffusion, and crystal-diffusion mechanisms [10]. 

VZLA - V3Lb = -SA - SB +2SC Also, the volume must remain constant. Therefore, 

To show that boundary sliding must participate in the diffusional creep to maintain compatibility, suppose that all of the SA, SB, and Sc sliding displacements are zero. Equations 16.44 require that the LA, LB, and Lc must also vanish. Therefore, nonzero Sl s (sliding) are required to produce nonzero grain-center normal displacements. 

This result can be demonstrated similarly by solving for the strain, s, along the applied tensile stress axis shown in Fig. 16.4 in terms of only the L1 s or only the S1 s  

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