共查询到20条相似文献,搜索用时 14 毫秒
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The effect of strain reversal on hardening due to high pressure torsion (HPT) was investigated using commercially pure aluminium. Hardening is lower for cyclic HPT (c-HPT) as compared to monotonic HPT (m-HPT). When using a cycle consisting of a rotation of 90° per half cycle, there is only a small increase in hardness if the total amount of turns is increased from 1 to 16. Single reversal HPT (sr-HPT) processing involves torsion in one direction followed by a (smaller) torsion in the opposite direction. It is shown that a small reversal of 0.25 turn (90°) reduces hardness drastically, and that decrease is most marked for the centre region. These behaviours and other effects are interpreted in terms of the average density of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs). A model is presented that describes the experimental results well. A key element of the model is the assumption that at the very high strains developed in severe plastic deformation processes such as HPT, the dislocation density reaches a saturation value. The model indicates that the strength/hardness is predominantly due to GNDs and SSDs. 相似文献
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Using Post‐Deformation Annealing to Optimize the Properties of a ZK60 Magnesium Alloy Processed by High‐Pressure Torsion 下载免费PDF全文
Seyed A. Torbati‐Sarraf Shima Sabbaghianrad Terence G. Langdon 《Advanced Engineering Materials》2018,20(2)
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Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion 下载免费PDF全文
Saleh N. Alhajeri Abdulla I. Almazrouee Khaled J. Al‐Fadhalah Terence G. Langdon 《Advanced Engineering Materials》2018,20(1)
The effect of the initial annealing temperature on the evolution of microstructure and microhardness in high purity OFHC Cu is investigated after processing by HPT. Disks of Cu are annealed for 1 h at two different annealing temperatures, 400 and 800 °C, and then processed by HPT at room temperature under a pressure of 6.0 GPa for 1/4, 1/2, 1, 5, and 10 turns. Samples are stored for 6 months after HPT processing to examine the self‐annealing effects. Electron backscattered diffraction (EBSD) measurements are recorded for each disk at three positions: center, mid‐radius, and near edge. Microhardness measurements are also recorded along the diameters of each disk. Both alloys show rapid hardening and then strain softening in the very early stages of straining due to self‐annealing with a clear delay in the onset of softening in the alloy initially annealed at 800 °C. This delay is due to the relatively larger initial grain size compared to the alloy initially annealed at 400 °C. The final microstructures consist of homogeneous fine grains having average sizes of ≈0.28 and ≈0.34 µm for the alloys initially annealed at 400 and 800 °C, respectively. A new model is proposed to describe the behavior of the hardness evolution by HPT in high purity OFHC Cu. 相似文献
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Introduction of Planar High Pressure Torsion (P‐HPT) for Fabrication of Nanostructured Sheets 下载免费PDF全文
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Ultrafine-grained alloys fabricated by severe plastic deformation (SPD) have high strength but often poor uniform ductility.SPD via high-ratio differential speed rolling (HRDSR) followed by an annealing treatment was applied to Al0.5CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be achieved.The optimized microstructure was composed of an ultrafine-grained FCC matrix (1.7-2 μm) with a high fraction of high-angle grain boundaries (61 %-66 %) and ultrafine BCC particles (with a size of 0.6-1 μm and a volume fraction of 8 %-9.3 %) distributed uniformly at the grain boundaries of the FCC matrix.In the severely plastically deformed microstructure,the nucleation kinetics of the BCC phase was accelerated.Continuous static recrystallization (CSRX) took place during the annealing process at 1273 K.Precipitation of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC grains.The precipitation of the hard and brittle σ phase was,however,suppressed.The annealed sample processed by HRDSR with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14 %-20 %.These tensile properties are comparable to those of transformation-induced plasticity steel.Strengthening mechanisms of the severely plastically deformed alloy before and after annealing were identified,and each strengthening mechanism contribution was estimated.The calculated results matched well with the experimental results. 相似文献