Dependence on Temperature
Diffusion is governed by an Arrhenius equation:
Since all mechanisms of steady-state creep are in some way dependent on diffusion, we expect that creep rate will have this exponential dependence on temperature
Creep occurs faster at higher temperatures. However, what constitutes a high temperature is different for different metals. When considering creep, the concept of an homologous temperature is useful.
The homologous temperature is the actual temperature divided by the melting point of the metal, with both being expressed in K. In general, creep tends to occur at a significant rate when the homologous temperatures is 0.4 or higher.
Dependence on stress
The applied stress provides a driving force for dislocation movement and diffusion of atoms. As the stress is increased, the rate of deformation also increases. In general, it is found that
where n is termed the stress exponent. Prediction of the value of n from first principles is not easy, but its value does depend on which mechanism of creep is operating. For example, for diffusion creep its value is approximately 1, while for dislocation creep it is usually in the range 3-8.
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