[1] Diffusion creep results in plastic deformation rather than brittle failure of the material.
Some sites of atoms in the crystal lattice can be occupied by point defects, such as "alien" particles or vacancies.
Vacancies can actually be thought of as chemical species themselves (or part of a compound species/component) that may then be treated using heterogeneous phase equilibria.
The vacancies will start moving in the direction of crystal planes perpendicular to the maximal stress.
This means a crystalline material can deform under a differential stress, by the flow of vacancies.
Highly mobile chemical components substituting for other species in the lattice can also cause a net differential mass transfer (i.e. segregation) of chemical species inside the crystal itself, often promoting shortening of the rheologically more difficult substance and enhancing deformation.
Another way in which vacancies can move is along the grain boundaries, a mechanism called Coble creep.
Pressure solution is, like Coble creep, a mechanism in which material moves along grain boundaries.
) depends on the differential stress (σ or σD), the grain size (d) and an activation value in the form of an Arrhenius equation:[5]
It is difficult to find clear microscale evidence for diffusion creep in a crystalline material, since few structures have been identified as definite proof.
[6] In materials that were deformed under very high temperatures, lobate grain boundaries may be taken as evidence for diffusion creep.
Larger grain sizes can be a sign that diffusion creep was more effective in a crystalline material.