Experimental measurement and micromechanical modelling of the creep deformation behaviour of AISI type 310 stainless steel and pure polycrystalline magnesium

Experimental creep measurements on an AISI type 310 stainless steel and high purity polycrystalline magnesium have been conducted within the test temperature and applied stress ranges of 650;The experimental results are discussed in terms of dislocation network models for creep and the internal and effective stresses. The analysis indicates that the high value for F at low temperatures and/or low stresses is in agreement with the predictions of exhaustion theories where multiplication is not taking place and easily-moved dislocations are eventually exhausted. The low value measured for the apparent activation energy for creep upon loading (creep strain ;Examination of the experimental results lends support to the theoretical models based on dislocation link length distribution (dislocation network) models for recovery creep. This analysis gives the stress dependence of the steady-state creep rate, ;Micromechanical modelling was carried out for three aspects of creep, namely (i) the grain size effect in the creep and superplastic deformation of polycrystalline materials; (ii) simulation of the experimental creep results for a 310 stainless steel using the Ostrom-Lagneborg creep model; and (iii) a dislocation link length statistics model for the plastic deformation of crystalline materials. It is shown that: (i) during superplastic deformation, a solid polycrystalline material can be visualized as a two "phase" mixture, one flowing according to Newtonian viscous flow and the other deforming by power law creep; (ii) the simulation results for the 310 stainless steel obtained using the Ostrom-Lagneborg creep model are in good agreement with the experimental results and other independent studies on dislocation network models for creep; and (iii) the dislocation link length statistics model produces reasonable values for the strain-hardening coefficient and the recovery rate during a constant stress creep test, and for a strain rate change during a constant strain rate tensile test. (Abstract shortened by UMI.).