Shi Ding Wu

The formation of PSB-like shear bands in cyclically deformed ultrafine grained copper processed by ECAP

Cyclic deformation was performed on ultrafine grained copper processed by ECAP. Shear bands (SBs) and adjacent microstructures were investigated using electron channeling contrast in scanning electron microscope. The possible formation mechanism of SB was discussed based on the characteristic distribution of defects introduced by ECAP

Mechanical properties of a two-phase alloy Mg–8%Li–1%Al processed by equal channel angular pressing

The microstructural evolution and room temperature tensile properties of Mg-8%Li-1%Al alloy processed by equal channel angular pressing (ECAP) at 403 K were investigated. It was found that the strength could be improved pass by pass. The elongation-to-failure decreased dramatically after the first ECAP pass, but could be improved pass by pass during the subsequent ECAP procedure. The microstructure analysis gave the explanations for these phenomena

Microstructure, texture, grain boundaries in recrystallization regions in pure Cu ECAE samples

By means of equal channel angular extrusion (ECAE), pure Cu single crystal samples were processed down to the submicron scale. In some parts of the samples, recrystallization occurs at room temperature. The recrystallization mechanism was analyzed by SEM-EBSP and SEM-ECC techniques. The grain boundary character distribution (GBCD) and orientation distribution function (ODF) of the regions undergoing recrystallization were computed. The results show that the nuclei can be formed at the intersections of two different shear bands, and the microstructures and the grain boundary characters in these locations contribute to growth of recrystallized nuclei. The recrystallized grains had grown according to the Felthams mechanism

Scanning electron microscopy-electron channelling contrast investigation of recrystallization during cyclic deformation of ultrafine grained copper processed by equal channel angular pressing

Cyclic deformation has been performed at ambient temperature on ultrafine-grained copper processed by equal channel angular pressing. Observations by electron channelling contrast in a scanning electron microscope revealed that pronounced recrystallization occurred and several distinct dislocation configurations such as dislocation walls and labyrinth structures were found within the recrystallized regions. A model is proposed to account for the evolution of recrystallization, emphasizing that its development results from an interaction between the cyclic deformation and the growth of recrystallized regions. The formation of recrystallized regions of different sizes is discussed.

Microstructural Characterizations of Cu Processed by ECAP from 4 to 24 Passes

The microstructures of pure Cu processed by equal channel angular pressing (ECAP) from 4 to 24 passes were investigated. It was found that the microstructures of Cu samples with a small number of ECAP passes (4-8) were not inhomogeneous and the fraction of high-angle grain boundary (HAGB) was low (25~43%). While for the samples with many number of ECAP passes (12-24), the grains became more equiaxed-like and the GB misorientations exhibited double-peak distribution with high fraction (51~64%) of HAGB. It was dislocation cells formed in large grains of the few-pass samples, but subgrains in the many-pass samples. These characterizations suggested that ultrafine-grained (UFG) microstructures in the few-pass samples were not fully accomplished, while it was obtained after many passes (>12). It is believed that dynamic recovery during processing for many passes was attributed to the formation of UFG microstructures.

On the Stability of Defects and Grain Size in Ultrafine-Grained Copper during Cyclic Deformation and Subsequent Ageing at Room Temperature

Ultrafine-grained (UFG) pure Cu processed by equal channel angular pressing (ECAP) was subjected to cyclic deformation and subsequent ageing treatment at room temperature (RT) in order to investigate the stability of defects and grain size. Cyclic deformation for 1000 cycles at RT leads to a large decrease of internal stress. X-ray diffraction (XRD) shows that the stability of defects and grain size at RT in as-cyclic deformed sample is lower than that in as-processed sample and that a reduction of internal stress takes place prior to grain growth. TEM observations show that the microstructural evolution during ageing is characterized by normal grain growth accompanied with recovery within grain interior.

Orientation Evolution during Equal Angular Channel Extrusion of Copper Single Crystal

The orientation evolution in Copper single crystal during ECAE (in Route C) has been investigated experimentally for 90° die angle by X-ray diffraction and TEM-OIM. It is shown that after the previous three passes of ECAE, orientation evolutes with similar mechanism to the simple shear deformation. The grain subdivision occurs with the appearance of many low angle grain boundaries. After four times extrusions the ED of the samples remains stable, their ND rotates around the ED by about 20°. After five times extrusions the main texture component remains stable.

Influence of Stacking Fault Energy on the Microstructures and Grain Refinement in the Cu-Al Alloys during Equal-Channel Angular Pressing

The microstructural evolution and grain refinement of Cu-Al alloys with different stacking fault energies (SFEs) processed by equal-channel angular pressing (ECAP) were investigated. The grain refinement mechanism was gradually transformed from dislocation subdivision to twin fragmentation with tailoring the SFE of Cu-Al alloys. Concurrent with the transition of grain refinement mechanism, the grain size can be refined into from ultrafine region (1 m~100 nm) to the nanoscale (<100 nm) and then it is found that the minimum equilibrium grain size decreases in a roughly linear way with lowering the SFE. Moreover, in combination with the previous results, it is proposed that the formation of a uniform ultrafine microstructure can be formed more readily in the materials with high SFE due to their high recovery rate of dislocations and in the materials with low SFE due to the easy formation of a homogeneously-twinned microstructure.

A dramatic decrease of the dislocation velocity in Ni3Al single crystals under the influence of hydrogen

Abstract The effect of hydrogen on the average dislocation velocities in Ni 3 Al single crystals has been investigated by the etch-pit technique. It is found that the velocity is dramatically decreased by the charged high content of hydrogen and that the tension/compression asymmetry of the dislocation velocity is reversed. Detailed observation of the dislocation structure indicates that the motion of edge superkinks is seriously inhibited by hydrogen solutes. These results serve as a strong evidence for the mechanism of hydrogen strengthening in metals. The interaction between the solute H and the edge dislocations also throws a sidelight on the role of kinks in the flow stress anomaly in Ni 3 Al.

Superplasticity of Magnesium Alloy ZK40 Processed by Equal Channel Angular Pressing

The superplasticity and microstructure of magnesium alloy ZK40 processed by ECAP for 1 and 4 passes were investigated. Tensile experiments at 523 K showed that the elongation of ZK40 was improved with the increasing passes. The elongation-to-failure of ZK40 processed by ECAP for 4 passes tested at 523 K and strain rate of 1×10-4s-1 was 660%. The microstructural analyses explained these results.