Comparisons of self-annealing behaviour of HPT-processed high purity Cu and a Pb–Sn alloy.

Early published results have demonstrated that high purity Cu and a Pb–62% Sn alloy exhibit very different behaviour during high-pressure torsion (HPT) processing at room temperature and subsequent room temperature storage. High purity Cu showed strain hardening behaviour with a refined grain structure during HPT processing whereas a Pb–62% Sn alloy displayed a strain weakening behaviour because the hardness values after HPT processing were significantly lower than in the initial as-cast condition even though the grain size was reduced. During room temperature storage after HPT processing, high purity Cu with lower numbers of rotations softened with the time of storage due to local recrystallization and abnormal grain growth whereas the Pb–62% Sn alloy hardened with the time of storage accompanied by grain growth. Through comparisons and analysis, it is shown that the low absolute melting point and the high homologous temperature at room temperature in the Pb–62% Sn alloy contribute to the increase in hardness with coarsening grain size during room temperature storage

Evaluating the Paradox of Strength and Ductility in Ultrafine-Grained Oxygen-free Copper Processed by ECAP at Room Temperature

Oxygen-free copper of >99.95% purity was processed by equal-channel angular pressing at room temperature (RT) for up to 24 passes and then pulled to failure at RT using strain rates from 10-4 to 10-2 s-1. The results show that the microstrain increases with strain at the lower numbers of passes but decreases between 16 and 24 passes. Similar trends were found also for the dislocation density, the Vickers microhardness and the values of the measured yield stresses in tensile testing. X-ray diffraction measurements showed a minor increase in the crystallite size at the high strain imposed by processing through 24 passes. These results demonstrate the occurrence of dynamic recovery at the highest strain. In tensile testing at a strain rate of 10-3 s-1 the results gave a yield stress of ~391 MPa and an elongation to failure of 52% which is consistent with an earlier report using Cu of much higher purity but not consistent with an earlier report using Cu of the same purity

The stability of oxygen-free copper processed by high-pressure torsion after room temperature storage for 12 months.

Ultrafine-grained copper samples produced by high-pressure torsion were stored at room temperature for 12 months to investigate microstructural stability and the self-annealing phenomena. The results show that samples processed by low numbers of turns exhibit less thermal stability after storage for 12 months by comparison with samples processed by high numbers of turns. A significant decrease in the hardness was recorded near the edges of the discs processed by 1/4, 1/2 and 1 turn due to recrystallization and grain growth whereas a minor drop in hardness values was observed in the samples processed by 3, 5 and 10 turns. This drop in hardness was related to a recovery mechanism

Characteristics of grain refinement in oxygen-free copper processed by equal-channel angular pressing and dynamic testing.

Oxygen-free copper was processed by equal-channel angular pressing (ECAP) at room temperature for 1, 4 and 8 passes and then the ECAP specimens were further deformed by dynamic testing at 298 K using a strain rate of 10 s-1. Experiments were conducted to investigate the influence of the initial microstructures induced by ECAP on the subsequent grain refinement and mechanical properties after dynamic testing. The results show the strength of copper increased with increasing numbers of ECAP passes and a significant additional grain refinement was produced in the ECAP specimens through the dynamic testing. Thus, the initial grain sizes after ECAP for 1, 4 and 8 passes were ~16, ~4.4 and ~2.9 µm, respectively, and these values were reduced to ~400, ~330 and ~300 nm by dynamic testing, The grains were refined by conventional dislocation processes in the 1-pass specimen but there was evidence for dynamic recrystallization in the specimen processed by 8 passes

Solid-State Recycling of Light Metal Reinforced Inclusions by Equal Channel Angular Pressing: A Review

Solid-state recycling of light metals reinforced inclusions through hot Equal Channel Angular Pressing (ECAP) is performed to directly recycle metal scraps and reduce cost of material in engineering applications. The ECAP is one of the most important method in severe plastic deformation (SPD) that can convert light metals into finished products. This paper reviews several experimental and numerical works that have been done to investigate the effects of the ECAP parameters such as die angles, material properties, outer corner angle, friction coefficient, temperature, size of chips, pressing force, ram speed and direct effects of number of passes on the strain distributions. It also includes the performance enhancement of aluminium matrix composite reinforced ceramic-based particles that derived from direct recycled aluminium chips for sustainable manufacturing practices

Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg

© 2018, The Author(s). High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing