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Fundamentals of the physics of strength and plasticity of metals
Published in V.M. Greshnov, Physico-Mathematical Theory of High Irreversible Strains in Metals, 2019
A separate type of creep is diffusion creep, at which the mass transfer is carried out by individual atoms, i.e., as a result of diffusion in the stress field. In this case, diffusion of vacancies and a counterflow of atoms can occur both in the volume of grains and along their boundaries. In the latter case, the activation energy is much smaller.
Time-dependent deformations and failures
Published in M.L. Jeremic, Rock Mechanics in Salt Mining, 2020
With a decrease in the deformation rate or temperature the diffusion creep dominates. According to some investigations at high temperature a diffusion creep does not occur. On the basis of experimental data the diffusion creep in function of temperature could occur for stress values between 0.1 and 0.5 MPa.
A micropolar continuum model of diffusion creep
Published in Philosophical Magazine, 2021
At high temperatures, solid polycrystalline materials can deform by diffusion creep, where defects within the crystalline lattice move by diffusion. At scales much larger than the grain scale the material behaves as if it were a Newtonian viscous fluid, with an effective shear viscosity which depends on the grain size [1–4]. At the microscale individual grains can be considered as rigid bodies, which interact by the plating out or removal of material at grain boundaries, leading to a macroscale strain. Rigid bodies have both translational (velocity) and rotational (angular velocity) degrees of freedom to describe their motion. However, when a material is treated as a Newtonian viscous fluid at the macroscale, the microscale rotational degrees of freedom are lost, as the classical Cauchy continuum is based on point particles with only translational degrees of freedom.
Acceleration of nickel diffusion by high tensile stress in cold-worked type 316 stainless steel at 450°C
Published in Philosophical Magazine, 2018
Koji Arioka, Yoshiaki Iijima, Motoki Miyamoto
The creep deformation of metallic materials at high temperatures is one of the diffusional phenomena occurring under tensile stress. Nabarro [17] and Herring [18] proposed the well-known model of diffusion creep mechanism under tensile stress conditions at high temperatures and introduced a creep rate equation. The basic concept of the model is the formation of vacancies at grain boundaries perpendicular to the tensile stress and the migration to the direction of tensile stress and finally the annihilation of the vacancies at other grain boundaries. On the other hand, Kimura [19] proposed another mechanism which was based on the decrease of migration energy of a vacancy for the jump parallel to the direction of tensile stress. The final expression of the creep rate is similar to that given by the Nabarro–Herring model [17,18], although the formation energy of the vacancy is interchanged with its migration energy. It is well recognised that the activation energy for creep rate at high temperatures is nearly equal to the activation energy for self-diffusion. However, the creep phenomenon at high temperatures is not concerned with the enhanced diffusion of the present case, because the direction of the main high tensile stress is perpendicular to the diffusion direction, while the tensile stress along the diffusion direction is very low, being about 30 MPa, as described previously.