1,720,962 research outputs found
Evolution of microstructural homogeneity in copper processed by high-pressure torsion
No full textDisks of coarse-grained pure Cu were processed by high-pressure torsion (HPT) and the microhardness and microstructural parameters were used to reveal the evolution of homogeneity. It is shown that the microstructures at the centers of the disks are significantly refined by HPT and an essentially homogeneous microstructure is achieved at strains above 15. An analysis demonstrates that microstructural homogeneity is achieved most readily in materials having either high or low, rather than intermediate, stacking fault energies.<br/
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
Twinning via the motion of incoherent twin boundaries nucleated at grain boundaries in a nanocrystalline Cu alloy
No full textDirect observations of microstructural evolution in a two-phase Cu–Ag alloy processed by high-pressure torsion
No full textDisks of a coarse-grained Cu–28 wt.% Ag alloy were processed by high-pressure torsion, and the decorative eutectic regions were used to reveal the evolution of deformation. It is shown that the deformation starts at the peripheries of the disks in the form of local vortices and then spreads inwards with increasing the number of revolutions. The experimental evidence confirms that the center of the disk also experiences a strain after five revolutions.<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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Formation of fivefold deformation twins in an ultrafine-grained copper alloy processed by high-pressure torsion
No full textFivefold deformation twins (DTs) are formed in an ultrafine grain, with a size of 100 nm, of a Cu–16 at.% Al alloy processed by high-pressure torsion. Formation occurs through the sequential emission of partial dislocations from grain boundaries and other multiple twin boundaries. These observations confirm the emission of partial dislocations from multiple-fold nodes which can be attributed to increased twinnability via the introduction of Al atoms which lower the driving force for partial emission.<br/
Significance of stacking fault energy on microstructural evolution in Cu and Cu-Al alloys processed by high-pressure torsion
No full textDisks of pure Cu and several Cu–Al alloys were processed by high-pressure torsion (HPT) at room temperature through different numbers of turns to systematically investigate the influence of the stacking fault energy (SFE) on the evolution of microstructural homogeneity. The results show there is initially an inhomogeneous microhardness distribution but this inhomogneity decreases with increasing numbers of turns and the saturationmicrohardness increases with increasing Al concentration. Uniform microstructures are more readily achieved in materials with high or low SFE than in materials with medium SFE, because there are different mechanisms governing the microstructural evolution. Specifically, recovery processes are dominant in high or medium SFE materials, whereas twin fragmentation is dominant in materials having low SFE. The limiting minimum grain size (dmin) of metals processed by HPT decreases withdecreasing SFE and there is additional evidence suggesting that the dependence of dmin on the SFE decreases when the severity of the external loading conditions is increased
Enhanced strength–ductility synergy in nanostructured Cu and Cu–Al alloys processed by high-pressure torsion and subsequent annealing
No full textNanostructured Cu and Cu–Al alloys processed by high-pressure torsion were isochronally annealed to investigate the effects of the stacking fault energy (SFE) on strength and ductility. All metals exhibit a similar general trend that the strength decreases and the ductility improves with increasing annealing temperatures, and a notable enhancement of ductility was achieved only when the volume fraction of recrystallized grains exceeded ~80%. The strength–ductility synergy improves significantly with decreasing SF
- …
