ABSTRACT
Nabarro-Herring creep When material is subjected to differential stress, the differential stress sets up a vacancy concentration gradient at the scale of grain-size, which causes spatial distribution of vacancy. Therefore, vacancy flux will occur, producing creep. Creep caused by motions of vacancies through a self-diffusion mechanism is called Nabarro-Herring creep, which was first proposed by Nabarro in 1948 and improved by Herring in 1950. NabarroHerring creep is described in the form of
ε = αDSD d2
σ
kT
where T is temperature, DSD is the coefficient of self-diffusion, σ is the differential stress, d is the grain size, is the atomic volume, k is Boltzmann’s constant, and α is a numerical coefficient depending on the grain shape and the boundary conditions for σ . It is a linear rheology (n = 1, n is the stress sensitivity of creep rate at steady-state stage) with a high sensitivity to grain-size (the strain rate depends on the grain size as ε ∝ 1/d2).
