Crystal Orientation Evolution Research Articles

A polycrystal plasticity-cellular automaton integrated modeling method for continuous dynamic recrystallization and its application to AA2196 alloy

Continuous dynamic recrystallization usually dominates the microstructural evolution in hot working of aluminum alloys, in which the high-angle grain boundaries of new grains mainly originate from the gradual increase in subgrain misorientation angles. In this work, an integrated computational method is proposed to simulate continuous dynamic recrystallization process of aluminum alloys by coupling three-dimensional cellular automaton and visco-plastic self-consistent models. The stress response, dislocation accumulation and recovery, and evolution of crystal orientations are computed in the context of polycrystal plasticity; the formation and rotation of subgrains, followed by stored energy and curvature-driven boundary migration, are captured and visualized by cellular automaton. The non-octahedral slip mode {110}<110> is additionally introduced to capture the 〈001〉 texture during hot compression. A universal cell topology deformation method is adopted to achieve an effective track of grain morphology evolution during plastic deformation. The proposed simulation framework is validated through simulating the isothermal uniaxial compression process of AA2196 alloy under different temperatures and strain rates. The orientation dependence of CDRX during compression is numerically reproduced by correlating the subgrain formation and rotation process with the activation state of slip systems. The simulated macroscopic flow stress, 3D microstructure and inherent microstructural characteristics such as subgrain size, subgrain boundaries and textures are in good agreement with the experimental results. The proposed method provides an effective and efficient tool for multi-scale simulation of hot forming process of aluminum alloys.

Analysis of the mechanism of orientations evolution during hot rolling and mechanical properties of TiBw/TA15 composites based on crystal plasticity finite element model

An in-depth understanding of the crystal orientation evolution during hot rolling of TiB whisker (TiBw) /TA15 composites and the anisotropy of the as-rolled plates can help fully utilize the material properties. In this paper, the crystal plasticity finite element models of high-temperature (HT) β-phase and room-temperature (RT) α-phase were constructed from electron backscattering diffraction data. Based on this, the orientation evolution during hot rolling in the single-phase region and the effects of the matrix texture on the mechanical properties of the as-rolled plates were analyzed. The effect of TiBw on the anisotropy was studied by the composites finite element model. Results showed that the α-fiber texture of the β-phase was formed during HT rolling. This texture was converted to the T-texture of the α-phase at RT during cooling according to the Burgers orientation relationships. The TiBw had little effect on the matrix texture composition. The TiBw and matrix texture caused the matrix to have higher strength along the rolling direction and the transverse direction, respectively. The matrix texture dominated the difference in mechanical properties because its effect exceeded that of TiBw. The effect of the matrix on the mechanical properties was caused by the Schmid factors (SFs) and the critical resolved shear stress (CRSS) of the slip system together. The slip mode was influenced by SFs determined by the angular relationship between the crystal orientation and the loading direction. The CRSS of the activated slip system determined the yield strength.

Investigation of the grain deformation to orthogonal cutting process of the textured Alloy 718 fabricated by laser powder bed fusion

In the laser powder bed fusion (LPBF), the grains grow in preferential directions depending on the scanning strategies, which results in layer-by-layer builds of particular crystallographic textures. The unique microstructure formed by LPBF results in anisotropic properties of the built structure at both macro and micro levels. To understand the grain deformation of the textured alloy fabricated by LPBF in the high-strain-rate shear process, Alloy 718 was used as an example in this work. Bulk samples with different metallurgical textures were deliberately fabricated by LPBF via three laser rotation angles, namely 0°, 67° and 90°, and then four thin slices obtained from bulks were subjected to “quasi-in-situ” grain deformation investigation through orthogonal cutting (a simple shear loading condition). The evolution of crystal orientations and morphologies, including size and shape, were traced before and after shear deformation. A full-field crystal plasticity simulation was used to quantify the stress status for grains obtained from EBSD data. This for the first time reveals the crystallographic level deformation history for hundreds of microns during a high strain rate shear removal deformation. Due to the carefully retained deformation history (i.e., typical bulges and slip bands) on the surface, a repeated deformation pattern was observed, attributing to the non-homogeneous deformation of typical build-directional blocks. The most active slip trace of deformed grain was calculated and verified based on the dominated slip bands within individual grains. The slip trace direction and intensity were quantified for different textured Alloy 718. Since the slipping-based deformation for an orientated grain is represented by its most active slip trace, a deformation tendency map is obtained by combining the shear direction, slip system and grain morphology. It reveals that grains in high texture intensity workpieces generally follow the macro shear-based deformation, while with the decrease in texture intensity, the plastic anisotropy is significant at the grain scale. Grains with similar orientations may also result in localised deformation anisotropy due to the different morphologies.

Incorporating dynamic recrystallization into a crystal plasticity model for high-temperature deformation of Ti-6Al-4V

During hot deformation of (α+β) titanium alloys, the simultaneous action of strain and temperature in the (α+β) regime facilitates dynamic recovery, dynamic recrystallization (DRX), and phase transformations via non-equilibrium paths. DRX is manifested in the form of fine recrystallized α or β grains. In the present study, a two-phase crystal plasticity finite element framework (CP-DRX) has been developed which incorporates DRX kinetics into the crystal plasticity (CP) model to predict the flow characteristics of Ti-6Al-4V alloys during thermo-mechanical processing. The CP slip system parameters, as well as elastic properties from both α and β phases of Ti, are calibrated for different strain rate conditions. An EBSD-informed two-phase microstructure representation has been utilized in the CP-DRX framework to explore the time-dependent evolution of DRX microstructure and crystal orientation for different strain rate conditions. The proposed CP-DRX can capture the evolution of crystal orientation and plastic flow stress–strain response of polycrystalline Ti-6Al-4V during the deformation process. Furthermore, the proposed model is able to capture the softening behavior, observed in average stress–strain response from experiments performed using a Gleeble thermomechanical simulator and predict the recrystallization texture.

Synergetic evolution of the microscopic crystal orientation and macroscopic superconducting properties of REBCO tape under sever deformation

This study investigates crystal orientation evolution at microscopic level, and changes in the superconducting properties at macroscopic level of rare-earth-barium-copper-oxide (REBCO) superconductor tape under severe deformation. At the microscopic level, in-situ electron backscatter diffraction is used for real-time observation of the crystal orientation evolution during the entire tensile process. At the macroscopic level, the critical current (Ic) value and Ic angle dependence performance are systematically measured under different applied tensile stresses. By comparing the microscopic and macroscopic results, the synergetic evolution mechanism between them is successfully established. Stress at the initial descent point of the Ic value excellently fits the one where the (001)[100] orientation sharply decreases, thereby revealing the real Ic degradation mechanism of REBCO tapes. The application of a moderate applied tensile stress can increase the in-field Ic value and pinning force because new generated defects and strains act as pinning centers. A higher tensile stress can destroy the biaxial texture of the REBCO layer and become a significant barrier to the supercurrent flow. This research elucidates the REBCO degradation mechanism and may assist manufacturers in improving the electromechanical properties of commercial REBCO tape.

Shear deformation behavior and failure mechanisms of graphene reinforced Sn-based solder joints bonded by transient current

Graphene as a reinforcement is expected to improve the shear strength of solder joint. However, little is known about the deformation behavior and mechanisms of composite solder joints. In this study, sandwich joints are prepared using graphene nanosheets-reinforced Sn-Ag-Cu composite solder (GNSs/SAC) by transient current bonding technology in order to obtain dispersed graphene. Interrupted shear tests combined with orientation image microscopy are conducted at different strain to observe the morphology and crystal orientation evolution of solder joints in situ. Some twins rotate, and the orientation begins to spread during shear, while the orientation of large Sn grain shows a minimal change. Cracks tend to initiate and propagate along the boundary. The failure mechanisms of the solder joint is determined. Molecular dynamics results show that the strain concentration at the boundary. Continuous shear tests show that the shear strength was improved by approximately 50.7% with the addition of 0.1 wt% graphene. Based on microstructure analysis and calculation, load transfer is identified as the dominant strengthening mechanism for GNSs/SAC alloys, followed by Orowan system. Graphene does not refine the grain size of solder joints, and dislocation multiplication from thermal mismatch does not strengthen them.

Tensile deformation behavior of ferrite-bainite dual-phase pipeline steel

In-situ tensile test accompanied by electron backscatter diffraction (EBSD) analyses were performed on polygonal ferrite (PF) and bainite dual-phase steel, selected regions of interest were analyzed following plastic deformation of the steel. Deformation-induced crystal orientation evolution, localized strain concentration, slip transfer, and geometrically necessary dislocation (GND) density were tracked. Results revealed that heterogeneity deformation facilitated formation subregions with crystal orientation deviation in grain and fragmented the grain by the new low angle grain boundaries (LAGBs) or medium angle grain boundaries (MAGBs). The PF grains with ND//<111> preferred crystal orientation exhibited high orientation stability, and almost all load axes of the selected PF grains moved to the [101] pole, resulting in enhancing {111} <110> orientation component at high strain levels. With the lattice rotation during deformation, the high angle grain boundaries (HAGBs) can change to MAGBs, which was beneficial to maintain coordination deformation among grains. Localized strain concentration can be decreased by the slip transfer across the PF grain boundaries or bainite/PF phase boundaries, which reduced the risk of micro-void formation. Additionally, the variation of α12 GND tensor average value (Ave. α12) revealed that the ferrite was continuous plastic deformation, while the bainite occurred stage hardening. The required strain for the coordination deformation was controlled by strain hardening behavior.

Grain refinement of Al–Mg–Si alloy without any mechanical deformation and matrix phase transformation via cyclic electro-pulsing treatment

Abstract In general, the grains of an AA6061 alloy cannot be refined without mechanical and heat treatments. Interestingly, in this work, the grain refinement of AA6061 alloy is successfully realized by a cyclic electropulsing treatment without any plastic deformation or matrix transformation (NP&D). In addition, unlike the gradually decreased dislocation density and homogenized evolution of crystal orientations in cyclic conventional-treated samples, in the cyclic electropulse-treated samples, the dislocation motion in {111} slipping planes is activated so that the dislocation density, the intensity of the [101]//ED texture and the distribution of the{111} planes in the sample coordinate are enhanced with an increase in the number of treatment cycles. Moreover, the strength and ductility of the AA6061 alloy are both improved through cyclic electropulsing treatment. In contrast to the cyclic conventional-treated sample, the yield strength and elongation of the optimized cyclic electropulse-treated sample are enhanced by 72.1% and 2.1%, respectively. Consequently, the electropulsing treatment can be used as a promising approach for the grain refinement of NP&D materials. This discovery also provides a theoretical supplement to the evolution of the nonequilibrium microstructure of NP&D alloys.

Machine learning based surrogate modeling approach for mapping crystal deformation in three dimensions

We present a machine learning based surrogate modeling method for predicting spatially resolved 3D crystal orientation evolution of polycrystalline materials under uniaxial tensile loading. Our approach is orders of magnitude faster than the existing crystal plasticity methods enabling the simulation of large volumes that would be otherwise computationally prohibitive. This work is a major step beyond existing ML-based modeling results, which have been limited to either 2D structures or only providing average, rather than local 3D full-field predictions. We demonstrate the speed and accuracy of our surrogate model approach on experimentally collected data from a face-centered cubic copper sample undergoing tensile deformation.

Preparation of Polyethylene and Ethylene/Methacrylic Acid Copolymer Blend Films with Tunable Surface Properties through Manipulating Processing Parameters during Film Blowing.

Polymer films based on polyethylene (PE) and ionomer ethylene/methacrylic acid (EMAA) copolymer blend were prepared by film blowing, whose surface properties were tuned by varying processing parameters, i.e., take up ratio (TUR). Blends of PE/EMAA copolymer were firstly prepared by the melt-mixing method, before being further blown to films. The wettability of the film was investigated by measuring the contact angle/water-film encounter time, and optical properties, i.e., the haze and transmittance. The wettability was found to be enhanced with the increase of TUR. So too was the haze, while the transmittance was found to be almost independent of TUR. The XPS and AFM results directly show the increasing polar functional groups (–COO−) on the surface and roughness with increasing TUR. Further analysis of the 2D SAXS and WAXS unveiled the origin of the invariant transmittance, which resulted from the minor change of the crystallinity and the monotonic increase of the haze, with TUR resulting from the evolution of crystal orientation. In addition to other post-modification methods, the current study provides an alternative route to prepare large-scale PE films as the template for the advanced potential applications, i.e., covering in the layer of roof, the privacy of protective windows, and multitudes of packaging.

Hydrazine solution processed CuSbSe2: Temperature dependent phase and crystal orientation evolution

CuSbSe2 has attracted huge attention as an absorber material for thin-film solar cells due to its attractive optical and electrical properties, as well as earth-abundant, low-cost, and low-toxic constituent elements. However, different from the conventional inorganic absorbers such as CdTe, CuSbSe2 has a complicated phase space with at least five competitive phases such as Cu2Se, CuSe, Sb2Se3, Cu3SbSe4, and Cu3SbSe3 and crystallizes in two-dimension (2D) layered structure. Crystal phase and orientation strongly correlate with film properties and thus are crucial for device performance. In this paper, by varying the annealing temperature, we carefully investigated the phase, electrical properties and crystal orientation evolutions of hydrazine solution processed CuSbSe2 films. Intermediate Cu3SbSe3 secondary phase was identified, and the temperature dependent orientation change was observed, which is driven by the reduced surface energy, as supported by the first-principle calculations. Finally, a prototype thin film solar cell is fabricated, achieving 2.70% efficiency. Our theoretical calculation and experimental investigation demonstrated the importance of controlling phase composition and crystal orientation in the application for photovoltaics.

In situ synchrotron study of electromigration induced grain rotations in Sn solder joints

Here we report an in situ study of the early stage of microstructure evolution induced by electromigration in a Pb-free β-Sn based solder joint by synchrotron polychromatic X-ray microdiffraction. With this technique, crystal orientation evolution is monitored at intragranular levels with high spatial and angular resolution. During the entire experiment, no crystal growth is detected, and rigid grain rotation is observed only in the two grains within the current crowding region, where high density and divergence of electric current occur. Theoretical calculation indicates that the trend of electrical resistance drop still holds under the present conditions in the grain with high electrical resistivity, while the other grain with low resistivity reorients to align its a-axis more parallel with the ones of its neighboring grains. A detailed study of dislocation densities and subgrain boundaries suggests that grain rotation in β-Sn, unlike grain rotation in high melting temperature metals which undergo displacive deformation, is accomplished via diffusional process mainly, due to the high homologous temperature.

Evolution of Crystal Orientation in One-Dimensionally Confined Space Templated by Lamellae-Forming Block Copolymers

Polymer crystallites may exhibit preferred orientation when the crystallization is allowed to occur under the influence of spatial confinement. Using time-resolved wide-angle X-ray scattering (WAXS), we explore the time evolution of the preferred crystal orientation within one-dimensionally confined space constructed by the lamellar microdomains of two crystalline block copolymers, polyethylene-block-poly(dl-lactide) (PE-b-PDLLA) and poly(l-lactide)-block-polyethylene (PLLA-b-PE), where the developments of the parallel and the perpendicular orientation of PE and PLLA crystallites, respectively, were monitored from the early stage of crystallization. Both types of crystallites were randomly oriented at the early stage of formation. As crystallization proceeded further, the ensemble-average orientation progressively improved toward the preferred orientation type, and the rate of establishing the orientation exhibited the same dependence on crystallization temperature (Tc) as the crystallization kinetics. Fu...

Evolution of crystal orientation in snow during temperature gradient metamorphism

AbstractThe physical properties of snow are tied to its microstructure. Especially for the slow, plastic deformation of snow and firn, the crystal orientation is an important factor in addition to the geometry of the ice matrix. While micro-computed tomography measures the snow microstructure precisely, it gives no information about the orientation of the ice crystals. In this study, we applied a temperature gradient of 50 K m−1 to large blocks of undisturbed decomposed snow and sieved snow during 3 months. The mean temperature of the snow samples during the temperature gradient experiment was −20°C. Two closely spaced snow samples were taken before the experiment, then every week during the first month and afterwards every month. From each sampling, one sample was analyzed by micro-computed tomography and the other was used for thin sections. The orientation of the c-axis was measured in the thin sections using an automatic ice texture analyzer. Initial density was 30% higher in the sieved snow sample. Density and specific surface area evolved alike, while the fabric showed a different evolution between the two samples. The undisturbed snow evolved from a weak single-maximum fabric towards a weak girdle fabric, while the sieved sample showed no evolution. The undisturbed snow sample converged toward the sieved sample fabric after 6 weeks, but continued its evolution thereafter. We suggest that the main factor causing this different behavior is the difference in density and in pore size.

Crystal orientation changes: A comparison between a crystal plasticity finite element study and experimental results

Tension tests on single-crystalline and bicrystalline austenitic stainless steel samples at ambient temperature and constant crosshead speed have been carried out. To understand the limits of crystal plasticity models in predicting the microstructural evolution process, simulation data were compared to experimentally observed crystal orientation evolution and strain analyses. The microstructure was captured after deformation by using electron backscatter diffraction and local strain analyses by digital image correlation. The initial grain orientation, sample geometry, boundary conditions and high-angle grain boundaries have enormous influences on the crystal orientation evolution. Strain gradients and rigid body rotation can be captured from the crystal plasticity model of Bassani & Wu. However, the description of the substructural fragmentation process lies beyond the capability of the model used. Slight modifications on the model by activation of slip systems and the implementation of a structural length scale delivers the experimentally observed substructures.

A study of intergranular fracture in an aluminium alloy due to hydrogen embrittlement

This work concerns a study of the effects of plasticity on the mechanism of intergranular cracking assisted by hydrogen induced embrittlement in an aluminium alloy. Here, tensile specimens charged with hydrogen were used to investigate quantitatively the effect of plastic deformation on the mechanism of intergranular crack initiation at the scale of the individual grains. An experimental procedure was set up to monitor the evolution of surface strain fields on in situ tested SEM notched specimens using digital image correlation techniques. In addition, measurements of the associated crystal orientation evolution at the micron scale were carried out using electron backscatter diffraction (EBSD). These measurements were then compared with finite element predictions of the local strain fields on the observed regions of the in situ specimen. The numerical predictions were obtained using a dislocation mechanics-based crystal plasticity model to describe the constitutive behaviour of each individual grain. The crystallographic grain orientations of the region of interest were discretised for the finite element analyses from EBSD maps. From this study, it was found that intergranular cracking due to hydrogen embrittlement in the Al alloy is locally triggered by high tensile grain boundary tractions, here estimated to be 170±35MPa. As importantly, the results also revealed that the conditions needed for grain boundary microcracks to initiate are greatly affected by the deformation of neighbouring grains: i.e. it was established that boundaries between two “hard” grains, inside a neighbourhood of “softer” deformed grains, are the first to fail.

The preferential growth of pyrite films prepared by thermal sulfuration of Fe2O3 films

Pyrite thin films were prepared by the sol–gel dip coating process and sulfuration treatment. The evolution of crystal orientation for the pyrite films was investigated as a function of sulfuration temperature. And the effect of crystal orientation on the electrical and optical properties was studied. It was found that films show (111) preferred orientation after sulfurized at low temperature. However, the (200) and (311) mixed preferred orientations were observed when pyrite films were sulfurized at higher temperature. Experimental results also indicate that the carrier concentration is high when the films show (111) preferred orientation. And the optical absorption coefficient is also large when the films grow with (111) preferred orientation. It is speculated that surface free energy could play a more important role in determination of preferred orientation when films were sulfurized at low temperature. However, the strain energy plays a more important role in determination of preferred orientation when films were sulfurized at higher temperature.

Flow Memory and Stability of Shear-Induced Nucleation Precursors in Isotactic Polypropylene

The dissolution of flow-induced nucleation precursors in isotactic polypropylene is investigated indirectly by means of in situ rheo-SAXS measurements. The progress of crystallization and the evolution of crystal orientation are recorded in isothermal conditions after a controlled shear step followed by an annealing step of different duration at various melt temperatures. The results confirm that the survival time of shear-induced nucleation precursors is extremely large compared to typical rheological relaxation times and it is longer for the precursors originated at higher shear rate. Most important, we show that the effect of flow on the development of oriented morphologies is lost much earlier than that on the overall crystallization kinetics. A schematic model for precursors’ dissolution involving gradual transformation from row into point-like nuclei is proposed.

On microstructure and texture heterogeneities in single crystals deformed by equal channel angular extrusion

An investigation of cross-section deformation heterogeneities resulting from equal channel angular extrusion (ECAE) of a cube-oriented nickel single crystal – extruded through a squared section die – has been carried out. It is demonstrated that, even for a given initial single crystal orientation, strong differences in crystal orientation evolution and associated deformation patterns can develop locally. In particular, a significant heterogeneity prevailing along the transverse direction of the billet is reported for the first time.

126 結晶成長における単結晶から多結晶への自発的遷移に関する方位進展とフラクタル次元(OS16.フェーズフィールド法とその応用(5),オーガナイズドセッション)

126 結晶成長における単結晶から多結晶への自発的遷移に関する方位進展とフラクタル次元(OS16.フェーズフィールド法とその応用(5),オーガナイズドセッション)