Polycrystal Plasticity Simulations Research Articles

Achieving high efficiency in reduced order modeling for large scale polycrystal plasticity simulations

Reduced order models for the nonlinear response of heterogeneous microstructures typically require a construction (or training) stage to build the reduced order basis. In this manuscript, an efficient model construction strategy for the eigenstrain homogenization method (EHM) is presented. The proposed strategy relies on a parallel, element-by-element, conjugate gradient solver. Near linear scaling has been achieved with respect to the number of degrees of freedom used to resolve the microstructure. Linear scaling with respect to the number of pre-analyses required to construct the reduced order model (ROM) follows from the EHM formulation. Furthermore, a parallel implementation for fast evaluation of the constructed ROM has been developed using shared memory parallelization. It has been shown that for large microstructures with ≈10,000 grains, the total computational cost of evaluating the nonlinear response of a polycrystal could be reduced by approximately an order of magnitude using 32 cores with respect to serial ROM simulation. The present methodology has been verified using an additively manufactured polycrystalline microstructure of a nickel-based superalloy, Inconel 625. The capability of the developed framework to construct a ROM for such large microstructures, as well as the ability of the ROM to predict average and local quantities of interest has been demonstrated.

Structural inheritance controlled by olivine viscous anisotropy in fossil mantle shear zones with different past kinematics

Geophysical and geological observations hint for the presence in the lithospheric mantle of both active and fossil shear zones with varied past kinematics. Shear in the lithospheric mantle produces olivine crystallographic preferred orientations (CPO), which lead to dependence of the viscous behavior on the direction of the load. Yet, the role of anisotropic viscosity in the mantle is seldom considered in models of structural reactivation. Here, we present 3-D geodynamic finite-element models that quantify the strain and viscosity distribution in a lithosphere containing a fossil thrust (or extensional) mantle shear zone with variable orientation relatively to a new extensional or compressional tectonics. The results were compared to that of a fossil strike-slip mantle shear zone. The fossil olivine CPO in the shear zone produces an anisotropic response of the lithospheric mantle, which is modelled using a parameterized description of viscous anisotropy derived from polycrystal plasticity simulations. We found that CPO-induced reactivation of fossil extensional or thrust mantle shear zones is favored for dips 30–60°, with maximum strain localization if the load is normal to the trend of a fossil shear zone dipping by 45°-50°. This represents a broader range of reactivation potential than in fossil strike-slip mantle shear zones. Both fossil shear zones trending at 45° to the imposed load are reactivated regardless of their dip. For a given viscous anisotropy in the lithospheric mantle (i.e., fossil shear zone orientation), the associated strain localization in the crust is always higher under extensional reactivation, where strain rates may be up to ∼100 times higher than those in the (isotropic) surrounding crust. These results imply that viscous anisotropy associated with fossil mantle shear zones plays a key role in large-scale structural reactivation during successive tectonic episodes, shaping the current lithospheric architecture, such as in the Pyrenees and Norwegian margin.

A mechanism-based multisurface plasticity model for hexagonal close-packed materials with detailed validation and assessment

We present a multi-surface model (MSM) of plasticity to simulate the anisotropic and asymmetric yield responses often observed in hexagonal close-packed (HCP) materials such as magnesium and its alloys. Motivated by the salient outcomes from high-resolution polycrystal plasticity simulations and experimental insights on magnesium alloys, we propose a three-surface representation incorporating two separate anisotropic, symmetric yield surfaces for the soft (basal) and hard (non-basal) glide, and an anisotropic, asymmetric yield surface for extension twinning. This reduced representation of the high-resolution crystal plasticity offers computational attractiveness to analyze large-scale engineering simulations while maintaining key micromechanical details of soft versus hard glide. The model is calibrated to a particular three-dimensional dataset for polycrystal magnesium alloy and is validated against a range of crystal plasticity results for different loading conditions. The capability of the model is then assessed for complex boundary-value problems at the macroscale (round notched bars) and at the microscale (void growth and coalescence). The validation and assessment demonstrate the ability of the proposed MSM to capture finer details of deformation such as identifying regions where soft and hard glide may occur around the void or in other heterogeneous loading states.

Nano-structuring of a high entropy alloy by severe plastic deformation: Experiments and crystal plasticity simulations

The evolution of microstructure, texture, and mechanical properties of an induction melted non-equiatomic Al6Co23.5Fe23.5Mn23.5Ni23.5 (at.%) high entropy alloy subjected to severe plastic deformation was investigated experimentally and by simulations. Analyses using electron backscatter diffraction and transmission Kikuchi diffraction images revealed the evolution of the microstructures. The coarse-grained initial structure was deformed down to an average grain size of 50 nm after a shear strain of 11 by employing the high-pressure compressive shearing process, at room temperature. Transmission electron microscopy analysis showed the presence of nano-twins. The high deformation led to a significant increase in the strength, up to ≈ 1.0 GPa. X-ray diffraction macro-texture analysis revealed a shear texture with the dominance of the B/B¯{112}110-type component whose intensity varied with strain. A two-step Taylor-type polycrystal plasticity simulation approach reproduced the texture by a correlation value of 91%. In the first part of the modeling, grain fragmentation was simulated, while in the second part, grain boundary shearing and deformation twinning were considered together with the operation of {111}112-type partial slip. The effect of twinning was also examined in the texture modeling and the simulations estimated that its fraction was less than 2%.

Initial grain orientation controls static recrystallization outcomes in cold-worked iron: Insight from coupled crystal plasticity/vertex dynamics modeling

Recrystallization of metallic materials is an important metallurgical treatment to bring cold-worked alloys to a usable state. Static recrystallization (SRX) occurs after deformation, once the material has built up sufficient plastic strain energy to trigger grain boundary motion. However, we have very limited knowledge about the combined effects on recrystallization kinetics of temperature, amount of cold working, triple junction mobility, and level of recovery in the deformed microstructure. In particular, little is still known about the microstructural factors that control the onset of SRX. Here we develop a comprehensive physical model based on coupling crystal plasticity and grain boundary kinetics utilizing curvature and differential plastic strain energy as driving forces for SRX in polycrystalline iron. The model links finite-element polycrystal plasticity simulations with a two-dimensional vertex dynamics approach, and is used to probe the large parameter space influencing static recrystallization. Our main finding is that the initial texture (defined by the polycrystal’s grain orientation and size distribution) is the dominant feature triggering and controlling SRX kinetics. We find a direct correlation between the degree of dislocation density buildup and the relative grain orientation across a grain boundary at the beginning of the deformation phase. Indeed, analysis of our results points to the maximum Schmid factor of a grain as the best predictor for activation of its grain boundaries during the recrystallization phase. We also find that the amount of post-deformation recovery only has a limited effect on the evolution of the recrystallized microstructure. Finally, using a definition based on the rate of transformation of the material, we find a recrystallization temperature of 600 ∘C, consistent with experimental observations in high-purity iron specimens.

Fretting fatigue experiment and polycrystal plasticity simulation in Ni-based superalloy at room temperature and 650 °C

The fretting fatigue behavior of Ni-based polycrystal superalloys at room temperature and 650 °C was studied by fretting fatigue experiment, electron back-scattered diffraction (EBSD) and polycrystal plasticity simulation. The life results and fracture morphology were obtained. The grain morphology, misorientation parameters, high-angle and low-angle grain boundary and geometrically necessary dislocation (GND) density were analyzed by EBSD. A polycrystal plasticity fretting fatigue simulation framework considering microstructure was developed. The effects of grain boundary, contact edge and temperature on stress and dominant slip distribution were analyzed, and the evolution of the dominant slip system in the loading process was discussed.

Strain localization at longitudinal weld seams during plastic deformation of Al–Mg–Si–Mn–Cr extrusions: The role of microstructure

The current work was motivated by the increasing use of hollow aluminum extruded profiles for automotive applications and the need for a better understanding of the mechanical response of extrusion seam welds. Two Al–Mg–Si alloys were studied, one without Mn and one with 0.5 wt%Mn and 0.15 wt%Cr. A high temperature homogenization was applied, resulting in a high density of α-Al(Fe,Mn)Si dispersoids in the Mn containing alloy, and an essentially dispersoid free microstructure in the other. The alloys were extruded through a simple porthole die (with two ports) to produce a strip with a centerline weld seam. The Mn free extrudate had a recrystallized grain structure whereas the Mn and Cr containing material was unrecrystallised. There were significant spatial variations of microstructure between the weld seam and surrounding regions, in particular the crystallographic texture. Tensile tests were conducted with the loading direction perpendicular to the weld seam using digital image correlation (DIC) to characterize the local strain distribution. Strain localization and final fracture occurred at weld seam for the unrecrystallized material whereas these occurred away from the weld line in the recrystallized case. The role of local crystallographic texture was examined through polycrystal plasticity simulations using the visco-plastic self consistent code (VPSC). These simulations indicated that the weld seam region was mechanically stronger than the surrounding region for the recrystallized alloy and correspondingly weaker for the unrecrystallized case, thereby rationalizing the experimental results of strain localization and final fracture location.

Combining crystal plasticity and electron microscopy to elucidate texture dependent micro-mechanisms of tensile deformation in lath martensitic steel

A modified 9Cr-1Mo steel having lath martensitic microstructure has been subjected to the hot-rolling at three different temperatures followed by a normalization at 1025°C to form different crystallographic textures after thermomechanical processing. The samples hot-rolled at 875°C, 1000°C and 1050°C showed major texture components as Goss (i.e. {110}<001>), Cube (i.e. {001}<01¯0>) and Gamma (i.e. {111}<1¯1¯2>), respectively. Next, these samples have been uniaxial tensile tested at quasi-static strain rate at room temperature, and tensile properties are evaluated. The results indicated almost similar strength levels for Goss and Cube oriented specimens, and significantly reduced strength for Gamma oriented samples. However, the Cube and Goss oriented samples showed different strain hardening rates owing to the occurrence of deformation induced twinning and anti-twinning phenomenon as revealed by the Visco-plastic self-consistent polycrystal plasticity simulations. Simulation results were validated with experimental observations using high-resolution transmission electron microscopy. Anisotropic parameters have also been simulated considering the difference in initial crystallographic orientations. Study of deformation micro-mechanism at different length scale of martensitic units (e.g., prior-austenite grain, martensitic packets, blocks, sub-blocks, and laths) revealed negligible rotations at the prior-austenite grain level, whilst the lattice rotations were found to be significant at martensitic sub-block (i.e. variant) length scale. The investigation indicated that some specific types of martensitic variants generally participated in large lattice rotation during deformation for differently textured samples.

Effect of precipitation state on plastic anisotropy in sheets of the age-hardenable aluminium alloys AA 6016 and AA 7021

We analyse flow stress, work hardening and plastic anisotropy of two heat-treatable Al alloys of the AA 6xxx and AA 7xxx series in dependence on state and morphology of the age-hardening precipitates. Sheets in the solution heat-treated condition were subjected to various ageing treatments in order to vary the precipitation state while maintaining crystallographic texture and grain shape. Accordingly, differences in the anisotropy obtained for various temper conditions could directly be attributed to the precipitates. Plastic anisotropy was assessed from the in-plane variations in yield strength and plastic strain ratios (r values). The texture-induced anisotropy was further modelled with polycrystal-plasticity simulations; therewith, the anisotropy obtained in the solution heat-treated, i.e. particle-free, sheets could be explained. In alloy AA 6016 with shearable needle-shaped β′′-particles, the effect of precipitates on plastic anisotropy was negligible compared to the pervasive effect of texture. Alloy AA 7021 containing plate-like η′-particles with low aspect ratio displayed a noticeable weakening of the texture-induced anisotropy with progressing heat treatment and the resulting changes in precipitation state. This weakening of anisotropy was attributed to the development of non-directional back-stresses due to the storage of Orowan loops around the non-shearable η′-precipitates during the early stages of straining.

Combining Crystal Plasticity and Electron Microscopy to Elucidate Texture Dependent Micro-Mechanisms of Tensile Deformation in Lath Martensitic Steel

A modified 9Cr-1Mo steel having lath martensitic microstructure has been subjected to the hot-rolling at three different temperatures followed by a normalization at 1025 °C to form different crystallographic textures after thermomechanical processing. The samples hot-rolled at 875 °C, 1000 °C and 1050 °C showed major texture components as Goss (i.e. {110} ), Cube (i.e. {001} ) and Gamma (i.e. {111} ), respectively. Next, these samples have been uniaxial tensile tested at quasi-static strain rate at room temperature, and tensile properties are evaluated. The results indicated almost similar strength levels for Goss and Cube oriented specimens, and significantly reduced strength for Gamma oriented samples. However, the Cube and Goss oriented samples showed different strain hardening rates owing to the occurrence of deformation induced twinning and anti-twinning phenomenon as revealed by the Visco-plastic self-consistent polycrystal plasticity simulations. Simulation results were validated with experimental observations using high-resolution transmission electron microscopy. Anisotropic parameters have also been simulated considering the difference in initial crystallographic orientations. Study of deformation micro-mechanism at different length scale of martensitic units (e.g., prior-austenite grain, martensitic packets, block, sub-block, and laths) revealed negligible rotations at the prior-austenite grain level, whilst the lattice rotations were found to be significant at martensitic sub-block length scale. The investigation indicated that some specific types of martensitic variants generally participated in large lattice rotation during deformation for differently textured samples.

Microstructure, Texture and Mechanical Properties in Aluminum Produced by Friction-Assisted Lateral Extrusion.

The Friction-Assisted Lateral Extrusion Process (FALEP) is a severe plastic deformation (SPD) technique for producing metal sheets from bulk metal or powder in one single deformation step at room temperature. In the present work, aluminum Al-1050 was deformed by FALEP. Then, its microstructure was examined by EBSD; the crystallographic texture by X-ray; material strength, ductility, and the Lankford parameter by tensile testing; the latter also by polycrystal plasticity simulations. It is shown that the microstructure was highly refined, with the grain size reduced more than 160 times down to 600 nm under the imposed shear strain of 20. The obtained texture was a characteristic simple shear texture with a shear plane nearly parallel to the plane of the sheet. The yield and ultimate strengths increased by about 10 times and three times, respectively. The Lankford parameter was 1.28, which is very high for aluminum, and due to the specific shear texture, unusual in a sheet. All these exceptional characteristics of Al-1050 were obtained thanks to the efficiency of the FALEP SPD process, which is a promising candidate for industrial applications.

Full-field polycrystal plasticity simulations of neutron-irradiated austenitic stainless steel: A comparison between FE and FFT-based approaches

We compare two full-field approaches – a crystal plasticity finite element method (CP-FEM) and crystal plasticity fast Fourier transform-based (CP-FFT) method – for a specific crystal plasticity law introduced for neutron-irradiated austenitic stainless steel SA304L currently used in nuclear reactor vessel internals. This particular law is employed to identify and quantify possible advantages and drawbacks of the two approaches when used in the large-scale simulations to predict the effect of irradiation damage (e.g., crack initiation) in stainless steel microstructures. A comparison is performed in a polycrystalline context for different periodic Voronoi microstructures deformed under tension. Special emphasis is put on studying the performance of the two approaches in terms of mesh convergence analysis using aggregate models with different spatial discretizations. In the CP-FEM approach, the performance of linear as well as quadratic tetrahedral meshes is investigated. A similar performance between the CP-FEM and CP-FFT methods is demonstrated in a smaller 2-grain aggregate. However, a slower mesh convergence is observed for the CP-FEM method when comparing tensile responses of a larger 100-grain polycrystal. A drop in the convergence rate is much more pronounced on linear than on quadratic tetrahedral meshes. As a consequence, largest (average) grain boundary stresses are shown to be overestimated with the linear mesh CP-FEM approach, thus raising a concern of possible over-conservatism employed in the CP-FEM prediction of crack initiation in irradiated stainless steels. On the contrary, the mesh convergence of the CP-FFT approach is found to be practically independent of the applied macroscopic strain and also aggregate size. Therefore, for such steels, the CP-FFT approach seems to be better justified.

Effects of calcium on the activity of slip systems in AZ31 magnesium alloy

Magnesium is the lightest structural material, but its applications are very limited due to the intrinsic brittleness, which is attributed to the limited number of independent slip systems available at room-temperature. In the present study, accordingly, we investigated the effect of 0.5 wt% Ca addition on the activity of slip systems in AZ31 magnesium alloy (AZ31-0.5Ca). For this purpose, polycrystal plasticity simulation based on viscoplastic self-consistent model was used to simulate the texture of AZ31 alloys (with and without Ca) at 10% tensile deformation, and hence, to predict the relative activities of various slip systems in both alloys. The results confirmed that prismatic <a> slip is the dominated deformation system in AZ31-0.5Ca, leading to a higher ductility as compared to the AZ31 alloy. This, in turn, was attributed to the formation of (Mg,Al)2Ca intermetallic compound due to the Ca addition, as found by microstructural observations using scanning electron microscopy.

The effect of through thickness texture variation on the anisotropic mechanical response of an extruded Al-Mn-Fe-Si alloy

There is currently a significant scientific and industrial interest in developing material models for the simulation of plastic deformation of aluminum extrusions relevant to their forming and their response during in service events such as vehicle crash. The objective of this work is to evaluate the effect of through thickness crystallographic texture gradients on material mechanical behaviour. This has been studied using a combination of experiments (i.e. pilot scale extrusions and stress-strain curves with the R-value to characterize plastic anisotropy for different loading directions) and the visco-plastic self-consistent (VPSC) polycrystal plasticity simulations on a model alloy system. Two limiting conditions were examined, i.e. unrecrystallized and fully recrystallized conditions. The results of electron backscatter diffraction (EBSD) characterization show that there is a significant through thickness variation in texture for both cases. However, the implications of the texture gradient on the macroscopic plastic response were relatively minor for the unrecrystallized case but quite significant for the recrystallized case. This was manifested as a strong difference in the contraction of the surface layer compared to the centre of the extrudate, particularly in the case of tests at 45° and 90° to the extrusion direction. This was rationalized in terms of the differences in texture between the surface and the centre using VPSC simulations. Finally, it was proposed that this effect will be explored in future work as it may have important implications on the surface stress state which could affect damage initiation, growth and coalescence, particularly in bending situations.

Misorientation development in continuous dynamic recrystallization of AZ31B alloy sheet and polycrystal plasticity simulation

A series of electron backscattered diffraction (EBSD) experiments is carried out to explore nucleation features in the continuous dynamic recrystallization (CDRX) of AZ31 Mg alloy sheets at 200 °C. The CDRX mechanism that misorientation accumulated from the core area to grain boundary leads to nucleation of dynamic recrystallization grains around parent grains can be identified for the present fine-grained AZ31B Mg alloy rolling sheet. A crystal plasticity approach for DRX simulation is extended to simulate the hot deformation and CDRX of the AZ31B magnesium alloy sheets. The experimental results of uniaxial tension along rolling direction (RD) and compression tests along RD and normal direction of the AZ31B sheets at 200 °C are numerically investigated by the current model in terms of mechanical behaviors, grains’ rotation, textures orientation and grain size evolution. The VPSC-DRX model that considers multiple slip systems and indirectly incorporates the misorientation can reproduce well the stress-strain curves, r-values, grain size change and texture evolution. The introduction of DRX will change the slip mode activities at 200 °C. The VPSC-DRX model can better predict the texture evolution compared to the simulation results regardless of DRX effects.

Deformation, crystal preferred orientations, and seismic anisotropy in the Earth's D″ layer

We use a forward multiscale model that couples atomistic modeling of intracrystalline plasticity mechanisms (dislocation glide ± twinning) in MgSiO3 post-perovskite (PPv) and periclase (MgO) at lower mantle pressures and temperatures to polycrystal plasticity simulations to predict crystal preferred orientations (CPO) development and seismic anisotropy in D″. We model the CPO evolution in aggregates of 70% PPv and 30% MgO submitted to simple shear, axial shortening, and along corner-flow streamlines, which simulate changes in flow orientation similar to those expected at the transition between a downwelling and flow parallel to the core–mantle boundary (CMB) within D″ or between CMB-parallel flow and upwelling at the borders of the large low shear wave velocity provinces (LLSVP) in the lowermost mantle. Axial shortening results in alignment of PPv [010] axes with the shortening direction. Simple shear produces PPv CPO with a monoclinic symmetry that rapidly rotates towards parallelism between the dominant [100](010) slip system and the macroscopic shear. These predictions differ from MgSiO3 post-perovskite textures formed in diamond-anvil cell experiments, but agree with those obtained in simple shear and compression experiments using CaIrO3 post-perovskite. Development of CPO in PPv and MgO results in seismic anisotropy in D″. For shear parallel to the CMB, at low strain, the inclination of ScS, Sdiff, and SKKS fast polarizations and delay times vary depending on the propagation direction. At moderate and high shear strains, all S-waves are polarized nearly horizontally. Downwelling flow produces Sdiff, ScS, and SKKS fast polarization directions and birefringence that vary gradually as a function of the back-azimuth from nearly parallel to inclined by up to 70° to CMB and from null to ∼5%. Change in the flow to shear parallel to the CMB results in dispersion of the CPO, weakening of the anisotropy, and strong azimuthal variation of the S-wave splitting up to 250 km from the corner. Transition from horizontal shear to upwelling also produces weakening of the CPO and complex seismic anisotropy patterns, with dominantly inclined fast ScS and SKKS polarizations, over most of the upwelling path. Models that take into account twinning in PPv explain most observations of seismic anisotropy in D″, but heterogeneity of the flow at scales <1000 km is needed to comply with the seismological evidence for low apparent birefringence in D″.

Polycrystal plasticity simulation of extrusion of a magnesium alloy round bar: Effect of strain path non-uniformity

A flow line model is established and combined with the crystal plasticity method to simulate the extrusion process of a magnesium alloy round bar, and investigate the effect of strain path non-uniformity on development of texture and microstructure in extrusion. A parametric flow line model is established to characterize the material flow corresponding to different strain paths in the extrusion chamber. The polycrystal plasticity method coupled with a phenomenological dynamic recrystallization model is employed to analyze the evolution of texture and microstructure accompanying the deformation. The texture of material deformed near the central extrusion area shows the typical ring fiber texture in the (0001) pole figure, while the basal poles of the material deformed in the side areas tend to rotate backward to the extrusion direction, resulting from an increase of the activities of twinning and slip systems. The more refined microstructure is obtained in the side areas due to the higher strain rate. The difference of mechanical properties between center and side areas of the extruded bar are numerically investigated by simulating tension and compression by using different extrusion textures. Side material shows more isotropic mechanical property than central material, and then less twinning is operative in compression.

Measuring and modeling the anisotropic, high strain rate deformation of Al alloy, 7085, plate in T711 temper

Al alloy 7085 in the T711 temper has been proposed as a lightweight metallic armor material. The room temperature constitutive response is assessed by compression testing at quasi-static (0.001 s−1) and dynamic (1000 s−1) strain rates along the rolling (RD), transverse (TD), and normal (ND) directions. The flow strength, plastic strain anisotropy (r-values) and texture evolution is measured along each direction. While the flow stress exhibits only mild anisotropy, the compressive r-values revealed strong strain anisotropy, with values close to 0.4 for RD, 0.8 for TD, and 0.6–0.8 for ND. The fracture response was also found to be anisotropic, with ND showing a lower compressive ductility as compared to the RD and TD. The level of anisotropy is essentially independent of the strain rate. However, flow softening and localization are more evident at dynamic rates. By employing self-consistent polycrystal plasticity simulation, the relative contributions of initial crystallographic texture, latent hardening and anisotropic grain shape effects were explored. The simulation results suggest that the ND and TD r-values are strongly affected by anisotropic grain shape, whereas the RD is rather insensitive to grain shape. Although the polycrystal model correctly predicts the mild flow strength anisotropy, the predicted strain anisotropy (variations in r value) are higher than that observed experimentally. Interestingly, assuming the grain shape to be equiaxed gives the best overall results, which suggests that the morphological texture does not play a major role in determining the anisotropy of materials such as the present heat treatable Al alloy.

Effect of Sn addition on the microstructure and deformation behavior of Mg-3Al alloy

Mg alloys generally suffer from their poor formability at low temperatures due to their strong basal texture and a lack of adequate deformation systems. In the present study, a small amount of Sn was added instead of Zn to Mg-3Al alloy to modify its deformation behavior and improve the stretch formability. Microstructural examinations of the deformed Mg-3Al-1Sn (AT31) alloy by electron backscatter diffraction and transmission electron microscopy show that prismatic <a> slip is quite active during deformation, resulting in much lower r-values and planar anisotropy than the counterpart Mg-3Al-1Zn (AZ31) alloy. Polycrystal plasticity simulation based on visco-plasticity self-consistent (VPSC) model also shows that prismatic <a> slip is the dominant deformation mode in AT31 alloy besides basal <a> slip. As a consequence, AT31 alloy shows a much higher stretch formability than AZ31 alloy. On the other hand, AZ31 alloy shows the development of intense shear bands during stretch forming, and these shear bands act as crack propagating paths, limiting the stretch formability of AZ31 alloy.

Two-phase deformation of lower mantle mineral analogs

The lower mantle is estimated to be composed of mostly bridgmanite and a smaller percentage of ferropericlase, yet very little information exists for two-phase deformation of these minerals. To better understand the rheology and active deformation mechanisms of these lower mantle minerals, especially dislocation slip and the development of crystallographic preferred orientation (CPO), we deformed mineral analogs neighborite (NaMgF3, iso-structural with bridgmanite) and halite (NaCl, iso-structural with ferropericlase) together in the deformation-DIA at the Advanced Photon Source up to 51% axial shortening. Development of CPO was recorded in situ with X-ray diffraction, and information on microstructural evolution was collected using X-ray microtomography. Results show that when present in as little as 15% volume, the weak phase (NaCl) controls the deformation. Compared to single phase NaMgF3 samples, samples with just 15% volume NaCl show a reduction of CPO in NaMgF3 and weakening of the aggregate. Microtomography shows both NaMgF3 and NaCl form highly interconnected networks of grains. Polycrystal plasticity simulations were carried out to gain insight into slip activity, CPO evolution, and strain and stress partitioning between phases for different synthetic two-phase microstructures. The results suggest that ferropericlase may control deformation in the lower mantle and reduce CPO in bridgmanite, which implies a less viscous lower mantle and helps to explain why the lower mantle is fairly isotropic.