Strain Rate Contribution due to Dynamic Recovery of Ultrafine-Grained Cu–Zr as Evidenced by Load Reductions during Quasi-Stationary Deformation at 0.5 Tm
Abstract
:1. Introduction
- demonstrate that the transient response to load changes can be studied in standard tensile creep machines with load control,
- show that the transient behavior of an ufg material is qualitatively the same as that of cg materials, including an initial period of strain mainly due to recovery,
- discuss the mechanism of dynamic recovery in qs and transient deformation with special regard to the influence of internal stresses.
2. Experimental Details
3. Results
3.1. Transients as Function of Time
3.2. Transients as Function of Strain
4. Discussion
4.1. Strain Related with Storage of Defects
4.2. Strain Related with Recovery of Defects
4.3. Comparison of Stress Dependences of and at Constant Structure
5. Summary
- In ufg Cu–Zr at recovery–strain connected with dynamic recovery of strain-induced crystal defects was found in tests with perturbation of the quasi-stationary (qs) state by load reductions. adds to the strain connected with dislocation generation and storage.
- The stress dependence of yields an activation volume consistent with the classical theory of thermally activated glide.
- The recovery–strain rate contributes 10% to 30% to the quasi-stationary strain rate . This fraction for ufg Cu–Zr with high volume fraction of HABs is similar to the one commonly reported for cg materials with high volume fraction of LABs. That could mean that boundaries play qualitatively similar roles in mediating dynamic recovery independent of their misorientation.
- The values of (at constant structure) and (at quasi-stationary structure) are relatively similar for large load reductions, even though the microstructures, in particular the dislocation structures, should differ significantly. This becomes understandable, if promotion of recovery by internal forward stresses is taken into account.
- Combining the rates of recovery–strain in the qs state and after perturbation of monotonic flow seems promising to better understand the mechanism of dynamic recovery of crystal defects, limiting the deformation strength under monotonic as well as cyclic loading conditions.
Author Contributions
Conflicts of Interest
Abbreviations
qs | quasi-stationary |
ECAP | equal channel angular pressing |
cg | coarse-grained |
ufg | ultrafine-grained |
LAB | low-angle boundary |
HAB | high-angle boundary |
Appendix A. Determination of Inelastic Strain
Appendix B. Activation Volume of Dislocation Glide
- is set equal to the expected spacing of free dislocations, , and
- is approximated by b,
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Blum, W.; Dvořák, J.; Král, P.; Eisenlohr, P.; Sklenička, V. Strain Rate Contribution due to Dynamic Recovery of Ultrafine-Grained Cu–Zr as Evidenced by Load Reductions during Quasi-Stationary Deformation at 0.5 Tm. Metals 2019, 9, 1150. https://doi.org/10.3390/met9111150
Blum W, Dvořák J, Král P, Eisenlohr P, Sklenička V. Strain Rate Contribution due to Dynamic Recovery of Ultrafine-Grained Cu–Zr as Evidenced by Load Reductions during Quasi-Stationary Deformation at 0.5 Tm. Metals. 2019; 9(11):1150. https://doi.org/10.3390/met9111150
Chicago/Turabian StyleBlum, Wolfgang, Jiři Dvořák, Petr Král, Philip Eisenlohr, and Vaclav Sklenička. 2019. "Strain Rate Contribution due to Dynamic Recovery of Ultrafine-Grained Cu–Zr as Evidenced by Load Reductions during Quasi-Stationary Deformation at 0.5 Tm" Metals 9, no. 11: 1150. https://doi.org/10.3390/met9111150