An ultra-high purity oxygen free high conductivity (OFHC) Cu was investigated to determine the evolution of microstructure and microhardness during processing by high-pressure torsion (HPT). Disks were processed at ambient temperature, the microstructures were observed at the center, mid-radius and near-edge positions and the Vickers microhardness was recorded along radial directions. At low strains, Sigma 3 twin boundaries are formed due to dynamic recrystallization before microstructural refinement and ultimately a stabilized ultrafine grain structure is formed in the near-edge position with an average grain size of similar to 280 nm after 10 turns. Measurements show the microhardness initially increases to similar to 150 Hv at an equivalent strain of similar to 2, then falls to about similar to 80 Hv during dynamic recrystallization up to a strain of similar to 8 and thereafter increases again to a saturated value of similar to 150 Hv at strains above similar to 22. The delay in microstructure and microhardness homogeneity by dynamic recrystallization is attributed to the high purity of Cu that enhances dislocation mobility and causes dynamic softening during the early stages of straining. (C) 2015 Elsevier B.V. All rights reserved.

The Pb-Sn alloy has a wide use in the electronic, energy storage and nuclear industries and a fine-grained Pb-Sn alloy may open up new possibilities for applications in these industries. In order to understand the behavior of grain refinement, a Pb-62% Sn eutectic alloy was processed by high-pressure torsion (HPT), stored at room temperature (RT) and then the microstructures of the alloy after HPT were repeatedly investigated during the course of self-annealing using electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is demonstrated that there is a large fraction of twin boundaries with a twin relationship of 62.8 degrees <100> in the microstructure of the initial as-cast condition. Due to the presence of the high imposed pressure, the mobility of Sigma 21 boundaries at 71 degrees is greatly favoured during processing by HPT. After the high pressure is removed, the mobility of dislocation-twin boundaries near 62.8 degrees<100> is then favoured. Processing by HPT significantly increases the solubility of Sn in the Pb phase. The supersaturated state of Sn in Pb is not stable during self-annealing at RT and instead a decomposition of Sn from the Pb-rich phase is observed after storage for 16 days. The main mechanism for this decomposition is lattice diffusion.

A supersaturated Al-Zn-Mg alloy was processed by dynamic plastic deformation (DPD) using a Split-Hopkinson pressure bar (SHPB) facility with strain range from 0.5 to 1.5 and then subjected to compressive testing at strain rates of 1 x 10(-3) -4 x 10(3) s(-1). The results show that there is concurrent occurrence of grain refinement, increase in dislocation density and precipitation of fine precipitates in different morphologies during DPD at strain over 1. This enhances the yield strength of the Al alloy after DPD over the as-received material in peak-aging state (T6). Grains are refined through the formation of low angle grain boundaries (LAGBs) by rearrangement of dislocations which leads to the subdivision of original grains. Heterogeneous coarse precipitates mainly of T (Al20Cu2Mn3) and E (Al18Mg3Cr2) phases distribute along dislocations and grain boundaries after DPD. Dynamic precipitation of very fine eta' and eta during DPD occurs where the volume fraction of precipitates increases with increasing the number of presses. The influence of precipitates on the strain rate sensitivity is also discussed.

Experiments were conducted to measure the extent of slippage occurring when thin disks are processed by high-pressure torsion. Separate tests were conducted on aluminum, copper and iron. The results show the extent of slippage varies between these three materials such that there is very little slippage in aluminum, slightly more slippage in copper and significant slippage when using iron. For all materials, the extent of slippage increases at both faster rotational speeds and lower imposed pressures. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

This review addresses new developments in the processing and properties of ultrafine-grained (UFG) materials. These materials are produced through the application of severe plastic deformation to conventional coarse-grained metals and typically they have grain sizes within the submicrometer or even the nanometer range. Although several techniques are now available for achieving excellent homogeneity and high fractions of high-angle grain boundaries, this review concentrates on the major procedures of equal-channel angular pressing and high-pressure torsion. It is shown that UFG materials exhibit both excellent strength at ambient temperature and, if the grains are reasonably stable, outstanding superplastic properties at elevated temperatures. These materials also have a high innovation potential for use in commercial applications.

Experiments were conducted to examine the effects of prior cold rolling and subsequent heat treatment on the microstructure, phase evolution and mechanical properties of an Fe-10Ni-7Mn martensitic steel. The results show that 70% cold rolling leads to deformation-induced austenite formation in the microstructure and reduces the size of the martensite blocks. Prior cold rolling increases the reversed austenite volume fraction under post-deformation intercritical annealing (PDIA) at 600 degrees C compared with the solution annealed condition. Electron back scattering diffraction and dilatometric studies showed that under PDIA there is a reverse transformation of martensite to austenite through a sequential combination of martensitic and diffusional mechanisms. There is also a precipitation of theta-NiMn particles in the PDIA specimen after subsequent ageing leading to an increase in the ultimate tensile strength in tensile testing. Cyclic tensile testing revealed pseudoelastic behavior in the cold-rolled specimen but this disappeared after PDIA and appeared again after subsequent ageing.