Ideal Shear Texture Research Articles

Preparation of fine-grained/ultrafine-grained Nb521 alloy with superior mechanical property by friction stir processing

High strength-ductility synergy is difficult to achieve in Nb alloys. Although high strength has been achieved through severe plastic deformation (SPD) technology, led to low ductility in alloys. In this work, FSP technology was applied to treat Nb–5W–2Mo–1Zr-0.1C (Nb521) alloys in preparation of fine-grained (FG)/ultrafine-grained (UFG) Nb521 with excellent strength and ductility. The microstructure evolution and mechanical property improvement mechanism were systematically studied for Nb521 alloy through various characterization pathways. The research results indicated that UFG Nb521 alloy with a grain size of 0.63 ± 0.41 μm can be prepared using low shoulder plunge depth FSP (LPD-FSP), which is the first report of UFG Nb521 alloy. The main reason for the formation of onion rings structure in SZ is the periodic wear of the stirring tool, and the onion rings structure does not cause mechanical damage. The texture formed by Nb521 alloy under different processing parameters is off-axis shear texture, which matches the ideal shear texture of D2 (112‾)[111] after rotation. In addition, this study also elaborated on the refinement mechanism of the second phase particles (Nb, Zr) C in Nb521 alloy during FSP. This study also indicated that the increase in yield strength of FSP samples at room temperature is mainly determined by grain refinement. These findings provided new ideas for the development of high-performance niobium alloys.

Effect of Tool Geometry on the Microstructure of Friction Stir Welding of Copper and 316L Stainless Steel

The microstructure evolution during dissimilar friction stir welding of copper with stainless steel 316L is studied. The welding is performed in transparence configuration using tools of two different geometries. The joints are characterized by optical microscopy, scanning and transmission electron microscopy, electron backscattered diffraction, and microhardness. The microstructure and crystallographic texture of base metals are significantly affected. The joint produced using a shoulder of 8 mm in diameter is characterized by a copper nugget with refined grains. The texture of copper is dominated by component of the shear texture. The steel beneath the tool shows a grain refinement with grains of sub‐micron size and a texture which is close to the ideal simple shear texture. For the joint produced by the 16 mm diameter tool shoulder, the nugget consists of large grains of copper, while the steel beneath the tool shows small recrystallized grains of micrometer size. The texture in the steel is dominated by the component of the shear texture. The Cu/316L interface in both types of joint is of very good quality. In a detailed study of the interface, it is revealed that the welding of metals is achieved by mutual intense mechanical interlocking without formation of any intermetallic compounds.

Microstructure and texture evolution of friction stir lap welded dissimilar multi‑aluminum stack

This work investigates the microstructural evolution of a dissimilar multiple‑aluminum alloy stack (AA7055, AA7055, AA6022) produced by friction stir lap welding (FSLW). A through-thickness analyses of grain orientation map, grain size and distribution, strain distribution, and texture evolution by electron backscattered diffraction-based characterization technique were performed. Two different welding parameters (combination of tool rotation and traverse speed) were used to study the effects of the welding parameters on these microstructural characteristics. The study shows that higher welding speed and higher rotation speed of the FSLW tool yield finer grains. FSLW resulted in shear texture formation in the weld regions due to high welding speeds. This texture development in the nugget zone is consistent with shear deformation, and (111) pole figures show ideal shear texture components. The Stir Zone (SZ) exhibits shear texture (A/A ̅ and B/B ̅ components), consistent with other shear-assisted processes. Recrystallization mechanisms observed are CDRX in SZ and DDRX in TMAZ (Thermo-Mechanically Affected Zone). Interface analysis reveals the presence of oxide layers between different aluminum sheets, affecting joint mechanical performance. The mechanical property of the lap welded joints was presented in terms of microhardness distribution across the weld cross section. Slightly higher hardness in higher speed welding setup was observed throughout the SZ and AA6022 layer, indicating greater grain refinement and uniform grain structure distribution.

Towards enhancing the ductility of AZ31 Mg alloys by controlling twin orientation at various shear strain levels

In this work, a novel texture control strategy, shear strain-induced twin orientation regulation (SITOR), was employed to fabricate the Mg–3Al–1Zn (AZ31) alloy with significantly improved ductility. The SITOR-1P sample processed at 250 °C exhibited a homogeneous microstructure and an almost ideal shear texture (c-axes of grains tilted 45° from the extrusion direction to the transverse direction), which resulted in an enhanced fracture elongation from 14.3% to 30.6% owing to the high activity of basal slip when compared with as-extruded Mg alloys. With increasing shear strain, the concentration of shear texture components in the SITOR-4P sample increased, leading to further improvement in its mechanical performance. While specimens produced by the conventional shear strain-induced orientation regulation (SIOR) method also underwent the same 4 passes of shear deformation, both their texture deflection and performance enhancement remained limited. The current investigation proposes a viable way to largely activate basal slip via the SITOR scheme, therefore offering a fresh perspective for addressing the poor plasticity of Mg.

Rolling-sliding contact fatigue failure and associated evolutions of microstructure, crystallographic orientation and residual stress of AISI 9310 gear steel

In the present study, rolling-sliding contact fatigue (RSCF) failures of AISI 9310 gear steel were analyzed systematically, in terms of characterizing the fatigue life, evolution of microstructure and crystallographic orientation, and variation of microhardness and residual stress distributions. The RSCF experiments were conducted using a twin rollers fatigue test rig. The RSCF life of AISI 9310 steel roller decreased continuously with increasing the maximum Hertzian contact pressure, however, it could be effectively improved by additional shot peening process owing to the enhanced microhardness and compressive residual stress near the roller surface. The main fatigue damage characteristics near the roller surface were consisted of inclined cracks, micropitting, spallation and plastic deformation. Although the compressive residual stress was reduced by RSCF, there was an obvious increase in the microhardness which should be attributed to the refined microstructure, increased dislocation density as well as phase transformation from retained austenite to martensite. In addition, the accumulated plastic strain during RSCF resulted into development of several preferred crystallographic orientations corresponding to ideal shear texture components of body-centered cubic (BCC) materials that has been seldom reported.

Microstructure and mechanical properties of ultrafine grained 5052 Al alloy fabricated by multi-pass differential speed rolling

This study examined the microstructural evolution and mechanical properties of an ultrafine grained (UFG) Al alloy processed by multi-pass differential speed rolling (DSR). For DSR operations with a thickness reduction of 30% in each pass and a roll speed ratio of 1:4 for the lower and upper rolls, respectively, plastic strain was imparted to the samples that were rotated 180° along the longitudinal axis between the adjacent passes. As the number of operations increased, the deformed microstructure developed gradually from a band-like structure, which was observed after a single pass, to one consisting of nearly equiaxed ultrafine grains (≈0.7 μm) divided by high angle grain boundaries (GB) after four-pass DSR. A close microstructural observation using high resolution transmission electron microscopy showed that the GBs of the UFG Al sample were curved and wavy. Based on microstructural observations, the grain refinement mechanism occurring in the Al sample during multi-pass DSR was found to be governed by geometric dynamic recrystallization and continuous dynamic recrystallization. In addition, the deformation texture of the DSR-treated samples developed into the ideal shear texture consisting of a rotated Cube {001}<110> orientation and γ-fiber (<111>//ND) with increasing number of operations. The tensile test results showed that the strength of the deformed samples increased with decreasing grain size while its tensile ductility was sacrificed. Moreover, the contribution of the strengthening mechanisms, such as solid solution, precipitation, grain size and dislocation strengthening, were discussed.

Influence of asymmetric rolling on the microstructure, texture evolution and mechanical properties of Al–Mg–Si alloy

The influence of asymmetric rolling on the microstructure, texture and mechanical properties of Al–Mg–Si alloy was investigated comprehensively through finite element simulation (FEM), microstructure and texture characterization, and tensile testing. Cold rolling was applied by imposing different velocity ratios (from 1 to 1.75) between the upper and lower rolls. The results show that asymmetric rolling has some effects on the shear strain, microstructure, texture and mechanical properties. The shear strain always exhibits a non-uniform distribution throughout the sheet thickness, and it is closely related to the velocity ratio; improving the velocity ratio could result in a larger shear strain in the surface contacting the roll with a higher velocity. As the velocity ratio increases, the cold rolled alloy sheet contains an increasing number of fine equiaxed grains, and the solution-treated recrystallization grain structure gradually becomes fine. Unlike symmetric rolling, asymmetric rolling can result in the development of TD-rotated β fiber, and the rotation angle is largely dependent on the velocity ratio. Although no ideal shear texture E {111}<110> and F{111}<112> orientations were developed, the shear texture H{001}<110> orientation appears by applying a sufficient velocity ratio. After solution treatment, the velocity ratio has no influence on the texture component, but improving the velocity ratio can reduce the texture volume fraction. Asymmetric rolling plays a positive role in improving mechanical property. As the velocity ratio increases, there are increases in the strength, elongation and plastic strain ratio R, and a decrease in the planar anisotropy ΔR, which is likely attributable to the weak texture.

On the enhanced hardening ability and plasticity mechanisms in a novel Mn-added CoCrNi medium entropy alloy during high-pressure torsion

Microstructure and texture evolution during high-pressure torsion (HPT) of a novel Mn-added CoCrNi medium entropy alloy (Co33Ni33Cr19Mn15) is investigated for the first time. The alloy exhibited a rapid rise in hardness at relatively low shear strains (γ≤20). It is attributed to an extensive dislocation activity to achieve saturation in dislocation density of ~1016 m−2, combined TWIP and TRIP effects and microstructural refinement. At higher shear strain, hardness increased at much reduced rates owing to saturation of dislocation density, twin fault probability and the TRIP effect, besides continued grain refinement for severe nano-structuring led to subsequent strengthening. The FCC phase showed remarkable stability except a small degree of initial deformation-induced HCP martensitic transformation in an early stage of HPT. The ideal shear texture components were observed at low shear strain, and these continued to evolve up to 5 turns of HPT processing. For similar HPT processing conditions, the studied alloy showed superior hardness (~650 Hv) compared to a wide spectrum of FCC materials, which is ascribed to a combination of the strengthening mechanisms of Taylor hardening, the TRIP and TWIP effects and Hall-Petch strengthening resulting from the nano-structured grains having an average size of ~35 nm.

Effect of dislocation characteristics on electrical conductivity and mechanical properties of AA 6201 wires

Abstract Aluminum 6201 alloys (AA 6201) exhibit high electrical conductivity and are lightweight, thus suitable for substituting Cu alloys. However, studies on the mechanical properties of and texture evolution in these alloys are few. To determine the relationship between the mechanical and electrical properties of these alloys, their properties and drawing processes were analyzed at room temperature; for this purpose, annealing was performed at 350 °C. The dislocation behavior caused by annealing was investigated by electron backscattered diffraction (EBSD) and X-ray diffraction line profile analysis. EBSD was also used for observing the texture evolution caused by deformation and annealing. An increase in the strain led to the formation of an ideal shear texture, in line with the drawing processes. It is well known that hardness is inversely proportional to electrical conductivity. However, when the hardness of the deformed alloy with a strain of 1.38 was maintained even after annealing for a long time, the electrical conductivity gradually decreased. In other words, as the recrystallized grains were coarsened by reducing the dislocation density, the dislocations were more randomly arranged, resulting in a decrease in the electrical conductivity. Furthermore, a highly strained alloy has more randomly oriented grains, and thus, the evolution of texture changes. The direct relationship between texture evolution and electrical properties could not be determined, but it seems to be a composite effect of dislocation characteristics, texture evolution, and grain size. As noted, the dislocation characteristics and texture evolution affect the mechanical properties.

Grain Structure, Crystallographic Texture, and Hardening Behavior of Dissimilar Friction Stir Welded AA5083-O and AA5754-H14

This work investigated the effect of friction stir welding (FSW) tool rotation rate and welding speed on the grain structure evolution in the nugget zone through the thickness of the 10 mm thick AA5083/AA5754 weldments. Three joints were produced at different combinations of FSW parameters. The grain structure and texture were investigated using electron backscattering diffraction (EBSD). In addition, both the hardness and tensile properties were investigated. It was found that the grain size varied through the thickness in the nugget (NG), which was reduced from the top to the base in all welds. Reducing the rotation rate from 600 rpm to 400 rpm at a constant welding speed of 60 mm/min reduced the average grain size from 33 µm to 25 µm at the top and from 19 µm to 12 µm at the base. On the other hand, the increase of the welding speed from 20 mm/min to 60 mm/min had no obvious effect on the average grain size. This implied that the rotation rate was more effective in grain size reduction than the welding speed. The texture was the mainly simple shear texture that required some rotations to obtain the ideal simple shear texture. The hardness distribution, mapped for the nugget zone, and the parent alloys indicated a diffused softened welding zone. The heating effect of the pressure and rotation of the pin shoulder and the heat input parameter (ω/v) on the hardness value of the nugget zone were dominating. Tensile stress-strain curves of the base alloys and that of the FSWed joints were evaluated and presented. Moreover, the true stress-true strain curves were determined and described by the empirical formula after Ludwik, and then the materials strengthening parameters were determined. The tensile specimens of the welded joint at a revolution speed of 400 rpm and travel speed of 60 mm/min possessed the highest strain hardening parameter (n = 0.494).

Analysis of Deformation Behaviour and Residual Stress in Rotary Swaged Cu/Al Clad Composite Wires.

Both copper and aluminum are widely applicable throughout a variety of industrial and commercial branches, however, joining them in a composite provides the possibility of combining all their advantageous properties in one material. This study investigates uniquely sequenced copper–aluminum clad composite wires, fabricated via rotary swaging technology. The composites were processed at 20 °C and 250 °C to a diameter of 5 mm. Structural observations and the determination of residual stress within both elements of the swaged wires were performed via electron microscopy; the experimental results were correlated with numerical predictions. As shown in the results, both the applied swaging force and temperature affected the plastic flow, which had a direct influence on residual stress and texture development; the Alsheath elements exhibited ideal rolling textures, whereas the Cuwires elements featured ideal shear texture orientation. The grains within both the Alsheath elements of the 5 mm composite wire were refined down to sub-micron size. Structural restoration also had a positive influence on residual stress.

Texture evolution of an Al-8Zn alloy during ECAP and post-ECAP isothermal annealing

In this work, the texture evolution of an Al-8 wt% Zn alloy during equal channel angular pressing (ECAP) and post-ECAP isothermal annealing was systematically investigated by electron backscatter diffraction (EBSD). Special attention is paid to the influence of static recovery and recrystallization on ECAP texture. After 1 pass of ECAP, the sample shows a texture similar to the ideal shear texture. During further deformation, the less deformed coarse grains rotate towards ideal ECAP texture orientations. After 5 passes of ECAP, the main texture component can still be depicted by fibers f1-f3. However, the f1, f2 and f3 fibers become less completed, indicating the fading of f1-f3 fibers. The weakening of ECAP texture with increasing deformation strains is attributed to continuous dynamic recrystallization (CDRX). Isothermal annealing treatments of the as-ECAPed 5P samples at 200 °C and 350 °C show that the static recovery and recrystallization do not change orientations of the major ECAP texture components. Instead, a full recrystallization and subsequent grain growth lead to a slight increase in the maximum intensity of ECAP texture.

Evolution of Microstructure and Crystallographic Texture During Dissimilar Friction Stir Welding of Duplex Stainless Steel to Low Carbon-Manganese Structural Steel

Electron backscattered diffraction (EBSD) was used to analyze the evolution of microstructure and crystallographic texture during friction stir welding of dissimilar type 2205 duplex stainless steel (DSS) to type S275 low carbon-manganese structural steel. The results of microstructural analyses show that the temperature in the center of stirred zone reached temperatures between Ac1 and Ac3 during welding, resulting in a minor ferrite-to-austenite phase transformation in the S275 steel, and no changes in the fractions of ferrite and austenite in the DSS. Temperatures in the thermomechanically affected and shoulder-affected zones of both materials, in particular toward the root of the weld, did not exceed the Ac1 of S275 steel. The shear generated by the friction between the material and the rotating probe occurred in austenitic/ferritic phase field of the S275 and DSS. In the former, the transformed austenite regions of the microstructure were transformed to acicular ferrite, on cooling, while the dual-phase austenitic/ferritic structure of the latter was retained. Studying the development of crystallographic textures with regard to shear flow lines generated by the probe tool showed the dominance of simple shear components across the whole weld in both materials. The ferrite texture in S275 steel was dominated by D1, D2, E, bar{E} , and F, where the fraction of acicular ferrite formed on cooling showed a negligible deviation from the texture for the ideal shear texture components of bcc metals. The ferrite texture in DSS was dominated by D1, D2, I, bar{I} , and F, and that of austenite was dominated by the A, bar{A} , B, and bar{B} of the ideal shear texture components for bcc and fcc metals, respectively. While D1, D2, and F components of the ideal shear texture are common between the ferrite in S275 steel and that of dual-phase DSS, the preferential partitioning of strain into the ferrite phase of DSS led to the development of I and bar{I} components in DSS, as opposed to E and bar{E} in the S275 steel. The formations of fine and ultrafine equiaxed grains were observed in different regions of both materials that are believed to be due to strain-induced continuous dynamic recrystallization (CDRX) in ferrite of both DSS and S275 steel, and discontinuous dynamic recrystallization (DDRX) in austenite phase of DSS.

Texture evolution of a dilute aluminum alloy subjected to tube channel pressing

Although a significant grain refinement of dilute aluminum alloys subjected to tube channel pressing has been acknowledged, evolution of texture of these alloys through abovementioned process has been remained less considered. The aim of this study is to investigate the evolution of texture of a dilute aluminum alloy subjected to tube channel pressing. For this purpose, electron backscattering diffraction analysis is applied after imposition of 0, 1, 3 and 5 passes of the process. Results show that a relatively strong texture is developed during the process whereas 〈1 0 0〉 and 〈1 1 0〉 orientations of grains are nearly aligned to Z and R directions of tube, respectively. Although appearance of this texture can be explained by development of shear texture inside FCC metals, there is a little difference between the TCP developed texture and the ideal shear texture. This difference is due to imposition of multi-directional shear strains besides peripheral strains through the process which cause deviation of the developed texture from the ideal shear texture.

Crystallographic Texture Investigation of Thick Section Friction Stir Welded AA6082 and AA5083 Using EBSD

In the present work, a FEI Sirion FEG-SEM equipped with a Nordlys CCD camera controlled by HKL Channel 5 software has been used to characterize the crystallographic texture of 20mm thick friction stir welded AA6082-T651 and AA5083-O. The crystallogaphic texture has been nvestigated near the top surface of the weld nugget at the shoulder affected region and near the base of the nugget in the probe affected region. The crystallographic texture in the shoulder affected region is complex in terms of determing the local reference frame of deformation and it requires complicated rotations to resemble the ideal simple shear texture. This implies the complex deformation histroy experinced in this region. However, the crystallographic texture in the probe-dominated region is simple shear texture. This implies that the deformation conditions across the whole weld nugget in this region are mianly dominated by the shear deformation generated by the probe rotation with the forward motion of the tool only playing a minor role in determining the local deformation gradient. Alternating bands between (+)and (C) was observed in the NG region of FSWed AA6082. The existence of A component is observed with an existence of strong C texture component which implies that when the C component is strong it can be associated with the A texture components.The crystallographic texture of AA5083 at both the shoulder and the probe dominated region is weak relative to that of the AA6082 .

The Correlation of Stir Zone Texture Development with Base Metal Texture and Tool-Induced Deformation in Friction Stir Processing of Severely Deformed Aluminum

The texture development during friction stir processing (FSP) of 1050 aluminum severely deformed at the strain magnitude of 2.32 was comprehensively discussed. It was observed that the component \( \bar{B} \) of the ideal shear texture along with the cube texture was developed in the severely deformed base metal. The effects of base metal texture on the texture development of stir zone, thermo-mechanically affected zone, and heat-affected zone during FSP were examined. Also, the developed texture components in the vicinity of the FSP tool and the stir zone were correlated to the deformation induced by the rotating tool which consisted of pin and shoulder. The observed texture components in the longitudinal section of the stir zone were found coincided with the ideal shear ones, but different from those observed in the severely deformed base metal. It could be responsible for the fact that the material beneath the FSP tool is predominantly deformed and stirred by the shoulder rather than the pin. The independency of texture development in the stir zone from pin-induced deformation was also consistent with the observation associated with the stir zone geometry which was independent of the pin geometry. Microstructural evolutions in the regions located ahead of the FSP tool manifested the incident of static recovery and recrystallization as a result of the stored strain in the severely deformed base metal. These led to the development of almost random texture and the deterioration of base metal texture in this region. This suggested the independency of texture development in the stir zone from the texture of severely deformed base metal.

Influence of magnesium AZ80 friction stir weld texture on tensile strain localisation

Synchrotron diffraction was used to construct the first 2D texture maps of entire magnesium AZ80 friction stir welds and showed that basal slip is favoured along most of the advancing side interface, and to a lesser extent on the retreating side interface. Zones of grains optimally oriented for basal slip are known to be a major contributor to strain localisation leading to failure during transverse tensile tests. Profilometry results confirm that the basal plane orientation dominates strain localisation. Microtexture maps traversing the weld interfaces were used to describe the material flow within the weld using scatter from the ideal shear texture fibre. The current results are highly applicable to modelling the strength and ductility of these joints under transverse loading.

Microstructural characterization and mechanical performance of an AA2024 aluminium alloy — Pure copper joint obtained by linear friction welding

The present work deals with the microstructural and mechanical characterization of an AA2024 – pure Cu linear friction weld. A thorough study of the microstructural features in close contact with the interface led to propose a phenomenological mechanism of material flow. The interface is covered by a discontinuous layer of intermetallic compounds. Al2Cu, AlCu, Al2Cu3 and more particularly Al4Cu9 were detected. Two metastable phases, i.e. an Al3Cu2 compound and an out-of-equilibrium Al solid solution containing 13at.% Cu, were also identified at the interface and on the Al side, respectively. In accordance with the applied strain state during welding, ideal shear texture components were formed on both sides of the joint. Due to the formation of large intermetallic compounds, the mechanical resistance of the joint remains to be improved.

Texture and Lattice Distortion Study of an Al-6061-T6 Alloy Produced by ECAP

Equal channel angular pressing (ECAP) is a severe plastic deformation (SPD) technique that produces nanostructured materials. Based on a remarkable grain size reduction, this process has led to improve mechanical properties, such as yield strength, fatigue, UTS, etc. In this work the characterization of the microstructure of the aluminum 6061-T6 alloy; plastically deformed up to ¾ µ 6, by the ECAP process, following route Bc, is presented. For this purpose, the ECAP processed samples were characterized by means of X-ray diffraction (for texture and line pro fi le analysis) and transmission electron microscopy. The initial crystallographic texture vanished after one ECAP pass and a new, well de fi ned, shear texture C a was generated. For the subsequent ECAP passes, more shear components: A 1 a , B a and B a were also developed. From the orientation distribution function analysis, a shift (generally less than 15°) between some experimental maxima and the reported ideal shear texture positions was observed. From these results, it was found that the microstructure generated with this process was stabilized after the 5th ECAP pass. Finally, the micro-strain analyses, in addition to the texture and transmission electron microscopy, contributed to the understanding of the effec t of the physical and mechanical processes that were activated during the SPD-ECAP techniques

Analysis of shear deformation by slip and twinning in low and high/medium stacking fault energy fcc metals using the [formula omitted]-model

Experimental tests involving shear stresses allow material to be deformed to very high plastic strain by overcoming localization phenomena. The simple shear texture development, which is also common near the surface of rolled parts, is important to study since it is directly connected to the metal anisotropy. Crystal plasticity models are used to simulate large deformation plasticity and texture evolution. The main insufficiency of most existing models is that they are, in certain cases, unable to predict all type of experimentally observed textures as well as texture transitions. In this paper, we show that the polycrystalline ϕ-model can be used to compute simple shear crystallographic texture transition for face-centered cubic metals (fcc) at large strains. This model takes into account the grains interaction effects but without the Eshelby inclusion theory. Predicted results are compared to experimental shear textures for medium stacking fault energy (SFE) metals (i.e. copper) and low SFE metals (i.e. silver). We show that the ϕ-model is able to predict a clear shear texture transition characterizing a range of fcc metals having high/medium to low SFE. The twinning mechanism is included in the ϕ-model in order to improve the predicted shear textures for low SFE metals. The effect of twinning on the ideal shear texture components is shown and is consistent with experimental results from the literature.