A variant selection model for predicting the transformation texture of deformed austenite

The occurrence of variant selection during the transformation of deformed austenite is examined, together with its effect on the product texture. A new prediction method is proposed based on the morphology of the austenite grains, on slip activity, and on the residual stresses remaining in the material after rolling. The aspect ratio of pancaked grains is demonstrated to play an important role in favoring selection of the transformed copper ({311}〈011〉 and {211}〈011〉) components. The extent of shear on active slip planes during prior rolling is shown to promote the formation of the transformed brass ({332}〈113〉 and {211}〈113〉) components. Finally, the residual stresses remaining in the material after rolling play an essential part by preventing growth of the {110}〈110〉 and {100}〈uvw〉 orientations selected by the grain shape and slip activity rules. With the aid of these three variant selection criteria combined, it is possible to reproduce all the features of the transformation textures observed experimentally. The criteria also explain why the intensities of the transformed copper components are sensitive to the pancaking strain, while those of the transformed brass are a function of the cooling rate employed after hot rolling.     

A Theoretical examination of the plastic deformation of ionic crystals: II. analysis of uniaxial deformation and axisymmetric flow for slip on {110} 〈110〉 and {110} 〈110〉 systems

Numerical calculations of the Taylor factor and of lattice rotation have been performed for composite slip on {110} 〈110〉 and {110} 〈110〉 slip systems. Two types of deformation were considered: uniaxial deformation which requires single slip only, and axisymmetric flow which requires the activation of five independent slip systems. For lattice rotation, calculations were made for both tension and compression. A variable in these calculations is the ratio of the critical resolved shear stress for slip between the two slip modes. The implications of the theoretical results to deformation texture development and texture hardening in polycrystalline ionic materials are discussed.     

Calculation of the taylor factor and lattice rotations for bcc metals deforming by pencil glide

Values of the Taylor factorM and the corresponding lattice rotations for tension or compression have been computed for grains of various orientations postulated to slip on arbitrary planes in 〈111〉 directions. The stresses in each grain were first obtained by numerically maximizing the work expression subject to the constraints of the pencil-glide yield expressions. The derived value of M_ave = 2.733 is slightly lower than in the case of mixed {110}, {112}, and {l23} 〈111〉 slip and the computed rotations are in reasonable agreement with experiments on iron. In compression, 26 pct of the grains are predicted to rotate toward 〈100〉, although the 〈111〉 texture component develops faster. The computational method used can easily be applied to the determination of the mechanics of texture generation for arbitrary deformations. Formerly a summer Undergraduate Research Scholar at Carnegie-Mellon University, Pittsburgh, Pa.     

Observation of cold-rolling texture and partially recrystallized texture in polycrystalline 3 pct Si-Fe by high-resolution electron backscattered diffraction

Cold-rolling texture and partially recrystallized texture of polycrystalline 3 pct Si-Fe were investigated using high-resolution electron backscattered diffraction (EBSD) method. From the measurement on a deformed grain with {211}〈011〉∼{111}〈011〉 orientations, deformation bands with {12 4 1}〈014〉 orientation were found. It turned out that the orientation rotation relationship between deformation bands and surrounding deformed grain can be explained by the activation of the slip system, which has a common slip plane with an adjacent grain. Oriented nucleation of recrystallized grains with {12 4 1}〈014〉 orientation was observed in a deformed grain with {211}〈011〉∼{111}〈011〉 orientation. Exactly the same orientation relationship that was observed between deformed grain and the deformation bands was also observed between the deformed grain and the recrystallized grain. A hypothesis that recrystallization nuclei are generated directly from the deformation bands formed by an activation of the slip system that has a common slip plane of neighboring deformed grains was proposed from the present experimental results.     

A theoretical examination of the plastic deformation of ionic crystals: III. Mixed {110}, {100}, {111} 〈110〉 slip and approximate 〈110〉 pencil glide

Calculations have been made of the Taylor factorM and of the lattice rotation for crystals undergoing axisymmetric flow and deforming by approximate 〈110〉 pencil glide. Two types of approximate 〈110〉 pencil glide were considered: 1) mixed slip on {110}, {l00}, and {111} 〈110〉 systems and 2) slip on a set of equally spaced slip planes containing each (110) slip direction. The results indicate that the pencil glide mode tends to reduce the plastic anisotropy in axisymmetric flow in contrast to the 〈111〉 slip modes in bcc metals. The lattice rotation is such that the fiber axis tends toward 〈111〉 in tension (〈lOO〉minor tendency) and toward 〈110〉 in compression. This result is similar to that of {lll}〈110〉 slip in fcc metals. We have also calculated the Taylor factors for mixed {110}〈110〉 + {lll}〈110〉 slip and for mixed {l00}(110) + {lll}〈110〉 slip. These mixed modes, together with the {lll}〈110〉 and the mixed {l00}〈110〉 + {110}〈110〉 slip modes previously analyzed, constitute all possible slip modes among {lll}〈110〉, {l00}(110), and {ll0}〈110〉 systems accommodating an arbitrary shape change. The conditions governing the activation of the various mixed modes have also been determined.     

Evolution of Microstructure and Texture During Hot Compression of a Ni-Fe-Cr Superalloy

Superalloys are being employed in more extreme conditions requiring higher strength, which requires producers to forge products to finer grain sizes with less grain size variability. To assess grain size, crystallographic texture, and substructure as a function of forging conditions, frictionless uniaxial compression testing characteristic of hot working was performed on INCOLOY 945 (Special Metals Corporation, Huntington, WV), which is a newly developed hybrid of alloys 718 and 925, over a range of temperatures and strain rates. The microstructure and texture were investigated comprehensively using light optical microscopy, electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM) to provide detailed insight into microstructure evolution mechanisms. Dynamic recrystallization, nucleated by grain/twin boundary bulging with occasional subgrain rotation, was found to be a dominant mechanism for grain refinement in INCOLOY 945. At higher strain rates, static recrystallization occurred by grain boundary migration. During deformation, duplex slip along {111} planes occurred until a stable 〈110〉 fiber compression texture was established. Recrystallization textures were mostly random but shifted toward the compression texture with subsequent deformation. An exception occurred at 1423 K (1150 °C) and 0.001 seconds⁻¹, the condition with the largest fraction of recrystallized grains, where a 〈100〉 fiber texture developed, which may be indicative of preferential growth of specific grain orientations.     

Investigation of recrystallization and grain growth of copper and gold bonding wires

Copper bonding wires were characterized using electron backscatter diffraction (EBSD). During drawing, shear components are mainly located under the surface and 〈111〉 and 〈100〉 fiber texture components develop with similar volume fractions. Grain average misorientation (GAM) and scalar orientation spread (SOS) of the 〈100〉 component are lower than those of the 〈111〉 or other orientations. Also, 〈100〉 components grow into other texture orientations during recrystallization. Copper wires experience three stages of microstructure change during annealing. The first stage is subgrain growth to keep elongated grain shapes overall and to be varied in aspect ratio. The grain sizes of the 〈111〉 and 〈100〉 components increase. The volume fraction of the 〈100〉 component increases, whereas that of the 〈111〉 decreases. The second stage is recrystallization, during which equiaxed grains appear and coexist with elongated ones. The third stage is grain growth, which eliminates the elongated grains. The 〈111〉 and 〈100〉 grains compete with each other, and the 〈111〉 grains grow faster than the 〈100〉 grains during the third stage. Comparison of recrystallization and grain growth processes in copper and gold wires reveals many common microstructural features.     

Atmosphere change of vacuum to hydrogen and sharpness of {110}〈001〉 texture in thin-gaged 3 Pct Si-Fe alloy strips

Heating in vacuum finally resulted in a main {100}〈uvw〉 texture and a trace of {111}〈uvw〉 texture. However, the texture was changed to the {110}〈001〉 texture when the strip was heated in hydrogen or when the vaccuum was changed to hydrogen at a temperature T_c. As T_c increased, the sharpness of the {110}〈001〉 texture increased, resulting in the high magnetic induction. This can be understood in the light of surface segregation kinetics of sulfur.     

Microstructure and Texture Evolution of Cold-Drawn 〈111〉 Single-Crystal Copper

The evolution of microstructure and texture in drawn 〈111〉 single-crystal copper with strains from 0.28 to 4.12 was analyzed. The texture analysis shows that in drawn 〈111〉 single-crystal copper, grain subdivision takes place, and at high strains, fiber textures consist of 〈111〉 and 〈100〉. However, the distribution of fiber textures is inhomogeneous along the radial direction. 〈111〉 is located in the center of samples and 〈100〉 is near the surface. Comparison of the texture evolution of drawn 〈111〉 and 〈100〉 single-crystal coppers indicates that the initial orientation is an important factor affecting the ratio of fiber texture 〈111〉 to 〈100〉. The results of microstructure show that at strains lower than 0.28, microstructure can be characterized as dislocation cells and few microbands. When strains are more than 0.58, a large number of extended planar dislocation boundaries appear. At strains more than 1.96, most of the extended planar boundaries are parallel to the drawn direction.     

Effect of texture and microstructure on resistance to cracking of high-strength hot-rolled Nb-Ti microalloyed steels

Significant texture gradient in the through-thickness direction was observed in high-strength hot-rolled 560 and 770 MPa Nb-Ti microalloyed steels, characterized by polygonal ferrite and ferrite bainite microstructures, respectively. {113}〈110〉 was the most intense deformation texture in the two high-strength grades of Nb-Ti steels and was dominant in the midthickness region compared to 10 and 25 pct depth below the surface. The recrystallization texture of austenite, {100}〈001〉, transformed into {100}〈011〉 component in the ferrite and indicated an increase in the intensity with increase in depth for the Nb-Ti microalloyed steels. The {100}〈011〉 texture has a detrimental effect on the edge formabiity of steels. However, the midthickness plane contained considerable intensity of desired texture, {332}〈113〉, which is expected to offset the undesirable {100}〈011〉 texture resulting in superior edge formability and impact toughness of Nb-Ti steels, consistent with experimental observations.     

A Theoretical examination of the plastic deformation of ionic crystals: I. maximum work analysis for slip on {110} 〈110〉 and {100} 〈110〉 systems

Conditions for the simultaneous yielding on five independent slip systems necessary for polycrystalline plasticity, have been analyzed in the case of slip on {110} 〈110〉 and {110} {110} systems. These systems are prominent deformation modes in cubic ionic crystals. Since the {110} 〈110〉 slip mode provides two independent slip systems and the {110} 〈110〉 mode three, an arbitrary shape change requires the activation of both modes simultaneously. A systematic search has revealed 84 stress states which are capable of activating slip on five independent slip systems without exceeding the yield stress in the remaining systems. Seven slip systems (four from {110} 〈110〉 and three from {110} 〈110〉) reach the yield stress simultaneously in 48 stress states, while eight slip systems (four from each mode) reach the yield stress simultaneously in the remaining 36 stress states. Those stress states applicable to deformation by axisymmetric flow were identified using the maximum work analysis of Bishop and Hill. The variation of the Taylor factor M with axial orientation was also derived analytically based on these stress states.     

The evolution of annealing textures in 90 Pct drawn copper wire

An electrolytic copper rod was drawn in 24 passes to a 90 pct reduction in area and subsequently annealed under various conditions. The global texture of the drawn wire, as measured by X-ray methods, showed a fiber texture approximated by a strong 〈111〉 and a weak 〈100〉 component. However, its microtexture, as measured by electron backscattered diffraction (EBSD), indicated that the major 〈111〉+minor 〈100〉 duplex fiber texture was dominant only in the center region, while a relatively diffuse texture developed with a somewhat higher density of orientations having a 〈11w〉//wire axis in the middle and surface regions. The inhomogeneous texture in the as-deformed wire gave rise to an inhomogeneous microstructure and texture after annealing. When annealed at 300 °C or 600 °C for 3 hours, the wire developed a duplex fiber texture consisting of major 〈100〉+minor 〈111〉 components in the center region, a strong 〈100〉 fiber texture in the middle region, and a weak texture consisting of 〈111〉 and 〈100〉 components with the 〈111〉 component being slightly stronger in the surface region. When the drawn wire was annealed at the high temperature of 700 °C, the texture at short annealing times was similar to that of the wire annealed at the lower temperatures of 300 °C and 600 °C for 3 hours, but prolonged annealing gave rise to a texture ranging from the 〈111〉 to 〈112〉 components due to abnormal grain-growth that started in the surface region. The recrystallization texture consisting of the major 〈100〉+minor 〈111〉 components was explained by the strain-energy-release maximization (SERM) model, in which the recrystallization texture is determined such that the absolute maximum principal stress direction due to dislocations in the deformed state is along the minimum elastic-modulus direction in recrystallized grains. On the other hand, the abnormal grain-growth texture was attributed to grain-boundary mobility differences between differently oriented grain.     

Investigation of Prism ?a? Slip in Warm-Rolled AZ31 Alloy

Based on analysis of texture and in-grain misorientation axes (IGMA) distribution, we investigate the effects of initial orientation and deformation temperature on the rollability of magnesium alloy AZ31 and the associated deformation mechanisms. Plate samples oriented favorably for basal 〈a〉 slip exhibited the best rollability at room temperature, whereas under the warm-rolling condition, surprisingly, the plate oriented for prism 〈a〉 slip exhibited the best rollability. The enhanced rollability of the latter plate is attributed to increased activity of prism 〈a〉 slip, which exhibits a lower texture hardening rate than basal 〈a〉 slip. The increased activity of prism 〈a〉 slip is shown experimentally by the development of the á10[`1]0 ? \langle 10\bar{1}0 \rangle //RD texture and 〈0001〉-type IGMA distribution. Asymmetric texture is also suggested to impair the rollability of plate oriented for basal 〈a〉 slip.     

Mechanical properties of high-temperature alloys of AlRu

A number of alloys based on the binary CsCl (B2) compound AIRu are tough and also are ductile in compression at room temperature. Alloys that are substoichiometric in Ru tend toward intergranular brittleness, are enriched in Al at the grain boundaries, and are improved by the addition of 0.5 at. pct B. Al₄₇Ru₅₃ + 0.5 at. pct B underwent 33.6 pct true strain in compression at 23°C and work hardened to 3.1 GPa true stress. Dislocations of slip vectors 〈100〉, 〈110〉, and 〈111〉 have been identified by transmission electron microscopy (TEM) study of plastically deformed samples, so that ample slip systems appear to be present for compatible deformation of polycrystalline samples.     

Crystallographic texture in mechanically alloyed oxide dispersion-strengthened MA956 and MA957 steels

The crystallographic textures of two mechanically alloyed, oxide dispersion-strengthened steels have been studied in the as-deformed and recrystallized conditions. The MA956 steel, which has relatively large chromium and aluminum concentrations, is found to exhibit a strong 〈110〉 fiber texture in the extruded condition. Despite the larger degree of deformation imparted to MA957 during extrusion, its crystallographic texture is found to be rather weak. Significant differences have also been found in the texture after recrystallization heat treatments. These differences could not be explained on the basis of deformation or recrystallization theory. However, the discovery that under certain specific conditions MA957 partially transforms to austenite has helped rationalize the texture results. In particular, the austenite is found to form at the temperature where the extrusion process is usually carried out. The observation of austenite is found to be consistent with thermodynamic phase stability calculations and metallographic experiments.     

Development of recrystallization textures in 0.08%C steel

The present work investigates the effect of cold deformation on the evolution of microstructure and textures during recrystallization in 0.08%C steel. The cold rolling texture consists of partial α-fiber (RD//〈110〉) and complete γ-fiber (ND//〈111〉) along with Goss ({110}〈001〉) and cube ({100}〈100〉}) texture components. The sharpness of α-fiber, γ-fiber and cube component increases with the increase in rolling reduction from 70 to 85% while that of Goss component decreases. After recrystallization (750 and 800°C), the textures were composed of α and γ-fiber along with significant Goss components. The strength of γ-fiber decreases after annealing. The presence of Goss component in recrystallization textures is attributed to preferential nucleation in {111}〈112〉 type deformed grains.     

Influence of transverse rolling on the

The influence of transverse rolling passes on the recrystallization texture was investigated in an effort to strengthen the {111} 〈uvw〉 type components and reduce the intensity of the {100} 〈0vw〉 components, improve the uniformity of the microstructure, and refine the grain size in high-purity tantalum plate. Tantalum, from three different ingot breakdown processes, received an additional 80 pct reduction in the transverse direction (perpendicular to the ingot centerline) in the processing schedule prior to final annealing. This work investigated the influence of the additional transverse rolling passes on the development of texture in the as-rolled tantalum and also in rolled plus annealed tantalum. After annealing, the tantalum plates had significantly strengthened {111} 〈uvw〉 crystallographic orientations, not only for the side forged process, but also for the upset and side forged tantalum. For tantalum processed by extrusion, the transverse rolling did not improve the final recrystallized texture.     

Orientation distribution function analysis of the recrystallization texture in a boron-treated deep-drawing steel

The textural components present in a boron-treated deep-drawing quality nonaging steel, processed and annealed in the mill, have been determined using the orientation distribution function (ODF) analysis technique. The main components are a 〈111〉 fiber parallel to sheet plane normal or normal direction, ND, and an incomplete 〈337〉∥ND fiber. Minor {110}〈001〉, {310}〈001〉, {001}〈110〉, and {110} 〈110〉 orientations were also found. The texture on the whole is somewhat similar to that in A1-killed steels, but not as strongly developed. It is expected that this boron-treated steel would be suitable for moderate forming applications.     

Electropulsing Induced Texture Evolution in the Recrystallization of Fe-3 Pct Si Alloy Strip

Electropulsing induced texture evolution in the primary recrystallization of a Fe-3 pct Si alloy strip was studied using the electron backscattered diffraction technique. The results revealed that the electropulsing strengthened considerably the recrystallization of a cold-rolled Fe-3Si alloy strip. Various textures with high-energy storages, such as α (100)〈110〉, γ (111)〈110〉, γ (111)〈112〉, and G-texture (110)〈001〉, formed after several seconds of electropulsing treatment (EPT), depending on the intensity of electropulsing. The athermal effect of electropulsing is 319 times stronger than the thermal effect of electropulsing for the formation of the G texture. The mechanism of electopulsing induced texture evolution is discussed from the point of view of Gibbs free energy and dislocation dynamics.     

Deformation of metastable betaTi-15Mo-5Zr alloy single crystals

Deformation modes have been investigated in metastable beta Ti-15Mo-5Zr alloy single crystals using both transmission electron microscopy techniques and multisurface trace analysis. {332} twinning and 〈111〉 crystallographic slip were observed to occur at an initial stage of deformation depending on deformation axis. {332} twinning occurs in a crystal whose tensile axis lies around 〈111〉, while 〈111〉 slip appears in a crystal having the tensile axis in the neighborhood of 〈001〉 to 〈011〉. The twinning system which possesses the maximum resolved shear stress is always operative in both tensile and compressive deformations. Single crystals of this alloy exhibit an asymmetry of the active slip plane and of the yield stress in a manner similar to other bcc metals and dilute alloys.