1,720,981 research outputs found
Determining the optimal stacking fault energy for achieving high ductility in ultrafine-grained Cu-Zn alloys
No full textBulk ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) often have low ductility. A previous study demonstrated the possibility of lowering the stacking fault energy to simultaneously increase the strength and ductility. This paper demonstrates, there exists an optimal stacking fault energy for the best ductility in UFG Cu–Zn alloys processed by the same SPD processing. When the stacking fault energy is too low, the grain size lies below 15 nm after SPD processing and the stacking faults are saturated so that it is difficult to accumulate dislocations and deformation twins during the subsequent tensile testing. These results provide significant guidance for the future design of UFG and nanocrystalline alloys for achieving high ductilities
Influence of stacking fault energy on the minimum grain size achiieved in severe plastic deformation.
No full textDetermining the optimal stacking fault energy for achieving high ductility in ultrfine-grained Cu-Zn alloys
No full textInfluence of stacking fault energy on nanostructure formation under high pressure torsion
No full textCopper, bronze (Cu–10 wt.% Zn) and brass (Cu–30 wt.% Zn) were deformed by high pressure torsion (HPT) under a pressure of 6 GPa for five rotations. The stacking fault energies (SFEs) of copper, bronze and brass are 78, 35 and 14 mJ/m2, respectively, and their average grain sizes after the HPT processing were about 84, 54 and 17 nm, respectively. Deformation twins were found in all samples and their densities increased with decreasing SFE. This work demonstrates that under the same conditions of HPT a low SFE promotes the formation of nanostructures and deformation twins
The role of stacking faults and twin boundaries in grain refinement of a Cu–Zn alloy processed by high-pressure torsion
No full textA recent model developed to predict the smallest grain sizes obtainable by severe plastic deformation has worked well for materials with medium to high stacking fault energies (SFEs) but not for those with low SFEs. To probe this issue, experiments were conducted using a Cu–30 wt.% Zn alloy with a very low SFE of 7 mJ/m2 as the model material. High-pressure torsion was used as the grain refinement technique. The results indicate that stacking faults and twin boundaries play a key role in the grain refinement process such that the smallest achievable grain size is determined by the highest stacking fault and twin density that the system is able to produce. An amorphization of grain boundaries was also observed in the final structure. These observations are very different from those reported for materials having medium to high SFEs and they confirm the operation of a different grain refinement mechanism.<br/
Concurrent microstructural evolution of ferrite and austenite in a duplex stainless steel processed by high-pressure torsion
No full textA duplex stainless steel with approximately equal volume fractions of ferrite and austenite was processed by high-pressure torsion. Nano-indentation, electron backscatter diffraction and transmission electron microscopy were used to investigate the hardness and microstructure evolutions of the steel. Despite the different strain-hardening rates of individual ferrite and austenite, the microstructures of the two phases evolved concurrently in such a way that the neighbouring two phases always maintained similar hardness. While the plastic deformation and grain refinement of ferrite occurred mainly via dislocation activities, the plastic deformation and grain refinement process of austenite were more complicated and included deformation twinning and de-twinning in coarse grains, grain refinement by twinning and dislocation–twin interactions, de-twinning in ultrafine grains and twin boundary subdivision
Influence of equal-channel angular pressing on pPrecipitation kinetics in an Al-Zn-Mg-Cu alloy
No full textProcessing by equal-channel angular pressing (ECAP) affects the morphology of ? precipitates in an Al–Zn–Mg–Cu (Al-7136) alloy. It is shown by transmission electron microscopy that ECAP changes the orientation of precipitates and this influences the atomic configuration and the interfacial energy at the ?/?-Al interfaces. Consequently, ? precipitates adopt an isotropic growth mode and evolve into equiaxed particles. A three-dimensional atom probe analysis demonstrates that large ? precipitates formed in different numbers of ECAP passes are of similar composition. The coalescence of smaller precipitates, rather than the fragmentation of larger precipitates, dominates the precipitate evolution
The effect of dislocation density on the interactions between dislocations and twin boundaries in nanocrystalline materials
No full textThe interactions between dislocations and twinboundaries (TBs) are significantly affected by both intrinsic material properties and extrinsic factors, including stacking fault energy, the energy barriers for dislocation reactions at TBs, twin thickness and applied stress. In this study, dislocation–TB interactions in grains with different dislocationdensities were investigated and we conclude that the dislocationdensity also affects the dislocation–TB interactions. In a twinned grain with a low dislocationdensity, a dislocation may react with a TB to fully or partially penetrate the TB or to be absorbed by the TB via different dislocation reactions. Alternatively, in a twinned grain with a high dislocationdensity, dislocations tangle with each other and are pinned at the TBs, thereby making it unfavourable for further dislocation reactions to mediate dislocation penetration across the TB. This leads to an accumulation of dislocations at the TBs, raising the local strain energy, which, in turn, is released by the activation of secondary twins by partial dislocation emissions from the other side of the T
De-twinning via secondary twinning in face-centered cubic alloys
No full textWe report a de-twinning process via secondary twinning in face-centred cubic structures with low stacking fault energies. A duplex stainless steel was deformed using high-pressure torsion. Primary twins with an average twin boundary (TB) spacing of ?7 nm formed in the early stages of the deformation and this was followed by secondary twinning. The partial dislocations from the secondary twinning subsequently interacted with the primary TBs, leading to the de-twinning of the primary twins. As a result of the de-twinning process, the secondary twins with an average TB spacing of ?1.7 nm reached a maximum length of ?200 n
Grain boundary formation by remnant dislocations from the de-twinning of thin nano-twins
No full textWe report a grain boundary formation mechanism in face-centred cubic metals with low stacking fault energies. Severe plastic deformation produces primary nano-twins with a twin boundary spacing of several nanometres, followed by secondary twinning through the activation of Shockley partial dislocations. The partial dislocations interact with primary twin boundaries, resulting in de-twinning of the primary twins and producing very high densities of sessile dislocations. The accumulation of these dislocations produces new grain boundaries with neighbouring grains having similar orientations
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