Interpretation of high temperature plastic deformation in terms of measured effective stresses

Abstract

The microdynamics of elevated temperature deformation in single and polycrystalline Fe-3 % Si is examined in terms of measured minimum effective stresses. Effective stresses are obtained through the use of a new experimental technique based upon the response of dislocations to the internal and applied stresses. Primary and steady state creep are examined with respect to the measured minimum effective stresses. Modified stress relaxation and strain rate sensitivity techniques are used to study dislocation velocities at elevated temperatures. Dislocation density measurements are made in both steady state creep and stress relaxation experiments and are related to measured effective stresses. Results indicate that the effective stress dependence of the steady state strain rate can be described by e ̇ g3 s ∝ σ min ∗2 where σ min ∗ is the minimum effective stress. Measurements of the tota within the subgrains yielded, p m ∝ σ min ∗ under the assumption that a constant fraction of the total dislocation density within the subgrains is mobile. The indirect measurements of dislocation velocity indicate that at elevated temperatures both the internal stress and mobile dislocation density change reversibly as a unique function of the effective stresses during stress relaxation and strain rate sensitivity tests. Comparison of steady state strain rates with measured dislocation densities supports the assumption of a linear dislocation velocity-effective stress relation.