Index of content:
Volume 34, Issue 8, August 2008
- LOW-TEMPERATURE PHYSICS OF PLASTICITY AND STRENGTH
34(2008); http://dx.doi.org/10.1063/1.2967513View Description Hide Description
The microstructure and mechanical properties of ultrafine-grain (UFG) commercial-grade Al obtained by equichannel angular pressing (ECAP) are study in the temperature range . Transmission electron microscopy and x-ray diffraction methods are used to show that as the number of passes increases, the grain size decreases, the grain shape becomes increasingly equiaxial, and the dislocation density inside a grain and the character of the intergrain boundaries change. An increase of the coherent scattering region and a decrease of the level of microdeformations indicate that pressing decreases the total density of imperfections of the crystal structure inside grains. As temperature decreases, the yield stress, plasticity, and strain hardening rate of UFG and coarse-grain polycrystals increase substantially. The deformation of UFG polycrystals at becomes unstable (abrupt). The temperature dependences of the yield stress of UFG and coarse-grain polycrystals, where the form of these dependences is characteristic for thermally activated detachment of dislocations from short-range potential barriers, are studied. The differences observed in the dependences for UFG polycrystals are explained by a change in the nature of such barriers and the mechanism by which glide dislocations overcome them. The dependences of the yield stress and the coefficient of strain hardening on the grain size are obtained. It is determined that the Hall–Petch relation describes the function in the temperature interval . The Hall–Petch coefficient increases as temperature decreases. The function is monotonically decreasing at 295 and but is independent of at . The experimental data are discussed within the framework of existing notions about the influence of the microstructure produced by ECAP on the evolution of the dislocation density during subsequent deformation.