Initial Random Texture Research Articles

Restirring and Reheating Effects on Microstructural Evolution of Al-Zn-Mg-Cu Alloy during Underwater Friction Stir Additive Manufacturing.

Friction stir additive manufacturing (FSAM) can be potentially used for fabricating high-performance components owing to its advantages of solid-state processing. However, the inhomogeneous microstructures and mechanical properties of the build attributed to the complex process involving restirring and reheating deserve attention. This study is based on the previous research of the underwater FSAMed 7A04 aluminum alloy and adopts a quasi in situ experimental method, i.e., after each pass of the underwater FSAM, samples were taken from the build for microstructural observation to investigate the restirring and reheating effects on microstructural evolution during the underwater FSAM. Fine-grain microstructures were formed in the stir zone during the single-pass underwater FSAM. After restirring, the grain size at the bottom of the overlapping region decreased from 1.97 to 0.87 μm, the recrystallization degree reduced from 74.0% to 29.8%, and the initial random texture transformed into a strong shear texture composed of the C {110}<>. After reheating, static recrystallization occurred in the regions close to the new additive zones, increasing the grain size and recrystallization degree. This study not only revealed the microstructural evolution during the underwater FSAM but also provided a guideline for further optimization of the mechanical properties of the Al–Zn–Mg–Cu alloy build.

Polycrystal Simulation of Texture-Induced Grain Coarsening during Severe Plastic Deformation.

During severe plastic deformation (SPD), there is usually extended grain fragmentation, associated with the formation of a crystallographic texture. The effect of texture evolution is, however, coarsening in grain size, as neighbor grains might coalesce into one grain by approaching the same ideal orientation. This work investigates the texture-induced grain coarsening effect in face-centered cubic polycrystals during simple shear, in 3D topology. The 3D polycrystal aggregate was constructed using a cellular automaton model with periodic boundary conditions. The grains constituting the polycrystal were assigned to orientations, which were updated using the Taylor polycrystal plasticity approach. At the end of plastic straining, a grain detection procedure (similar to the one in electron backscatter diffraction, but in 3D) was applied to detect if the orientation difference between neighboring grains decreased below a small critical value (5°). Three types of initial textures were considered in the simulations: shear texture, random texture, and cube-type texture. The most affected case was the further shearing of an initially already shear texture: nearly 40% of the initial volume was concerned by the coalescence effect at a shear strain of 4. The coarsening was less in the initial random texture (~30%) and the smallest in the cube-type texture (~20%). The number of neighboring grains coalescing into one grain went up to 12. It is concluded that the texture-induced coarsening effect in SPD processing cannot be ignored and should be taken into account in the grain fragmentation process.

A Study of the Microstructure, Texture and Tensile Properties of 1060/Al-TiC/1060 Sandwich Composites Prepared by Hot-Roll Bonding

Microstructure and texture development in Al/AMCs sandwich composites and the connection between the tensile properties and microstructure/texture have not been fully understood. In this study, the AA 1060 aluminum alloy and spark plasma sintering (SPS) processed Al-TiC composite were prepared into the 1060/Al-TiC/1060 sandwich composites by hot-roll bonding (HRB). The influence of rolling reduction on the microstructure, texture and tensile properties was studied. An inhomogeneity of microstructure through the thickness of Al layer was observed after the HRB process. The grains at the surface Al layer were tilted to 19 deg with respect to the rolling direction after 34.8 pct reduction, and the tilted grains were developed to a deeper region with increasing rolling reduction. The degree of grain-subdivision and number of high-angle boundaries decreased as the observed area moved from the surface to the interface. The cube texture at the surface of the Al layer transformed into the rotated-cube shear texture during HRB process. The strength of the rotated-cube texture at the interface layer was lower than at the surface layer. The initial random texture in the Al-TiC layer was changed to the α-fiber and β-fiber rolling textures after the HRB process. The yield strength and ultimate tensile strength of the sandwich composites increased with increasing rolling reduction, and the sandwich composites showed a high elongation with 43.0 pct reduction.

Prediction of maximum fatigue indicator parameters for duplex Ti–6Al–4V using extreme value theory

Fatigue Indicator Parameters (FIPs) based on the cyclic plastic strain are used as surrogate measures of the driving force for fatigue crack formation. For a given microstructure, the Extreme Value Distribution (EVD) of FIPs can be populated using results of a number of digital Statistical Volume Element (SVE) instantiations analyzed by the crystal plasticity finite element method. The number of microstructure instantiations affects the maximum FIPs computed. To predict the maximum FIPs in a large volume of material using simulation results from a limited number of SVEs, we proposed a statistical approach based on extreme value theory. The predicted maximum FIP values are compared directly to simulation results of 1000 SVEs to validate the proposed method for duplex Ti–6Al–4V. It is shown that simulations of only 100 SVEs suffice to identify the statistical information for a reliable prediction of the maximum FIPs in polycrystalline duplex Ti–6Al–4V with initial random texture.

Prediction of Maximum Fatigue Indicator Parameters for Duplex Ti-6Al-4V Using Extreme Value Theory

Fatigue Indicator Parameters (FIPs) based on the cyclic plastic strain are used as surrogate measures of the driving force for fatigue crack formation. For a given microstructure, the Extreme Value Distribution (EVD) of FIPs can be populated using results of a number of digital Statistical Volume Element (SVE) instantiations analyzed by the crystal plasticity finite element method. The number of microstructure instantiations affects the maximum FIPs computed. To predict the maximum FIPs in a large volume of material using simulation results from a limited number of SVEs, we proposed a statistical approach based on extreme value theory. The predicted maximum FIP values are compared directly to simulation results of 1000 SVEs to validate the proposed method for duplex Ti-6Al-4V. It is shown that simulations of only 100 SVEs suffice to identify the statistical information for a reliable prediction of the maximum FIPs in polycrystalline duplex Ti-6Al-4V with initial random texture.

Deformation-induced crystallographic-preferred orientation of hcp-iron: An experimental study using a deformation-DIA apparatus

Shear and uniaxial deformation experiments on hexagonal close-packed iron (hcp-Fe) was conducted using a deformation-DIA apparatus at a pressure of 13–17 GPa and a temperature of 723 K to determine its deformation-induced crystallographic-preferred orientation (CPO). Development of the CPO in the deforming sample is determined in-situ based on two-dimensional X-ray diffraction using monochromatic synchrotron X-rays. In the shear deformation geometry, the 〈0001〉 and 〈112¯0〉 axes gradually align to be sub-parallel to the shear plane normal and shear direction, respectively, from the initial random texture. In the uniaxial compression and tensile geometry, the 〈0001〉 and 〈112¯0〉 axes, respectively, gradually align along the direction of the uniaxial deformation axis. These results suggest that basal slip (0001)〈112¯0〉 is the dominant slip system in hcp-Fe under the studied deformation conditions. The P-wave anisotropy for a shear deformed sample was calculated using elastic constants at the inner core condition by recent ab-initio calculations. Strength of the calculated anisotropy was comparable to or higher than axisymmetric anisotropy in Earth's inner core.

Microstructure and mechanical properties of equal channel angular pressed Mg–Y–RE–Zr alloy

The microstructure and mechanical properties of equal channel angular pressed (ECAP) Mg–Y–RE–Zr alloy (WE43) are examined. Results show that after ECAP, the average grain size remarkably decreases from ∼50 µm at initial state to ∼1.5 µm through ECAP for four passes and the homogeneity of microstructure also improves gradually. Meanwhile the secondary-phase β-Mg5RE morphology has obvious transformation from plate-like to spherical. Moreover, the initial random texture is converted to the strong (0002) basal texture. The ultimate tensile strength and yield strength increase in all passes. However, the ductility exhibits a tendency of increase from 1 to 4 passes then decrease from 4 to 12 passes. The variation in strength and ductility is attributed to the effect of specific microstructure evolution.

Additional relaxations in the Alamel texture model

The additional relaxation of the L12 shear components of the velocity gradient has earlier been suggested for the special case of rolling in the Lamel Taylor-type of texture aggregate model. This concept of so called type III of relaxation is here generalized to apply for general strain paths by a modification of the Alamel model. Relaxations are made for arbitrarily oriented grain boundary segments, for which only invariant relaxations are allowed. The Alamel+type III model is compared to other Taylor-like models (FC Taylor, Lamel, Lamel+type III, GIA, VPSC) for the case of cold rolling of an initial random texture, as well as for a strong cube texture. In both cases the new model gives improved texture predictions.

Effect of micro-elasticity on grain growth and texture evolution: A phase field grain growth simulation

A novel phase field grain growth model combined with a micro-elasticity effect including elastic anisotropy and inhomogeneity is developed to investigate the effect of micro-elasticity on the grain growth. Due to the elastic anisotropy of each grain and the elastic interaction with its neighbors, an external elastic load affects strongly grain growth and texture evolution. A strong 〈100〉//ND fiber texture developed in poly-crystalline Cu with an initial random texture by biaxial external strain, whereas a 〈111〉//ND fiber texture evolved under the biaxial external stress condition. In contrast to the previously reported macro-elastic descriptions, there was a strong localization of strain energy density and inhomogeneous distribution even inside grains, and the elastically soft grains with a higher strain energy density grew at the expense of the elastically hard grains to reduce the total strain energy. The results suggest the possibility of tailoring the texture by controlling various external loads.

Crystal plasticity analysis of texture development in magnesium alloy during extrusion

The texture development mechanism during the extrusion of magnesium alloy is investigated by experimental observation and numerical analysis. First, we perform a finite element analysis of a full extrusion process using a phenomenological constitutive equation, and it is confirmed that the loading condition of the extrusion process near the central axis of the billet is approximated by an equi-biaxial compression mode. Then, the equi-biaxial compression problem is adopted as a simplified boundary value problem to be solved using a crystal plasticity model to clarify the detailed texture development mechanism during the extrusion process. The crystal plasticity analysis of equi-biaxial compression successfully reproduces the texture development from an initial random texture to the final experimentally observed texture. The effects of the deformation modes (i.e. slip and twinning systems) implemented in the calculation and the reference stress ratio of basal to nonbasal slip systems on texture development are studied in detail. Finally, the mechanism of texture development during the extrusion process is discussed in terms of the lattice rotation caused by the activated slip systems.

Effect of Micro-Elasticity on Grain Growth and Texture Evolution: A Phase Field Study

In this presentation, a novel phase field grain growth model combined with a micro-elasticity effect including elastic anisotropy and inhomogeity is presented to demonstrate the effect of micro-elasticity on grain growth and texture evolution. We report on texture evolution and abnormal grain growth induced by external elastic load from the viewpoint of micro-elasticity and first demonstrate that the previous mechanism (macroscopic viewpoint) on the effect of external elastic load on grain growth does not work in strain-controlled system. In contrast to the macro-elastic descriptions, strong localization of strain energy density and inhomogeneous distribution even inside grains are observed. Moreover, elastically soft grains with a higher strain energy density grow at the expense of the elastically hard grains to reduce the total strain energy. It is observed that strong &lt;100&gt;//ND fiber texture was developed in poly-crystalline Cu with initial random texture by biaxial external strain while &lt;111&gt;//ND fiber texture evolved in biaxial external stress condition. Even, grain growth of &lt;100&gt;//ND textured grains is occurred as abnormal grain growth when &lt;100&gt;//ND textured grains are surrounded by &lt;111&gt;//ND fiber textured grains.

Computation of deformation-induced textures in electrodeposited nickel coating

The deformation-induced textures in electrodeposited nickel coating were numerically studied. The finite element method (FEM) for polycrystalline was developed based on Taylor model. Then the deformation-induced textures in electrodeposited nickel coating with initial random and lamellar texture were simulated under tensile load. It is found that the initial textures significantly influence the deformation-induced textures. For nickel coating with the initial random textures, when the tensile strain is about 40%, there are some lamellar textures. For nickel coating with the initial lamellar textures, the lamellar texture is more intensity with the increase of the tensile strain. With the increase of the tensile strain in the coating, there are more pronounced element distortion and a more inhomogeneous deformation. Due to the different crystal orientations, the grain-scale roughness is observed. With increasing tensile strain in the coating, the surface grain-scale roughness increases on the free surface. The surface roughness of the coating with initial random texture is lower than that with the initial lamellar texture.

Analysis of texture evolution of cubic metals by isotropic and anisotropic viscoplastic self-consistent models

The texture evolutions of cubic metals during tension, compression and rolling have been analyzed by isotropic and anisotropic self-consistent models with the large deformation theory of viscoplastic material. The final texture components predicted from an initial random texture were the same in both isotropic and anisotropic self-consistent models. The effect of rate sensitivity on the rolling texture component was analyzed. The intensity of the major Copper component of the rolling texture increased with the decreasing of rate sensitivity and the increasing of rolling strain.

Analysis of texture evolution in FCC metals by full constraint and a self-consistent viscoplastic model

The texture evolution of FCC metals during tension, compression and rolling has been analyzed by the full constraint Taylor model and self-consistent model with the large deformation theory of viscoplastic material. The final texture of tension and compression predicted from the initial random texture were similar in both full constraint Taylor and self-consistent models. The final rolling texture of the the full constraint Taylor model was the D-type texture, while that of the self-consistent model was the copper type texture due to lower interaction between single crystals and matrix.