Crystallographic Orientation Research Articles

Synthesis and characterization of graphene on copper foil via atmospheric pressure chemical vapor deposition method and its impact on electrical properties

Copper, prized for its exceptional electrical conductivity, thermal conductivity, and mechanical strength, is a staple in electronic applications. The ongoing quest for enhanced performance in miniaturized technologies has led to exploring copper-graphene composites, particularly those integrating bilayer graphene (BLG). This study investigates the enhancement of electrical conductivity in copper through the incorporation of BLG via atmospheric pressure chemical vapor deposition (APCVD). The research highlights the APCVD method's ability to grow high-quality BLG on high-purity oxygen-free copper foil, demonstrating significant improvements in electrical properties. Detailed characterization reveal that the graphene growth process induces structural changes in the copper, promoting ideal crystallographic orientations and larger grain sizes. This process achieves nearly complete graphene coverage and results in a copper/graphene (Cu/GR) composite with minimal defects. The electrical conductivity of the Cu/GR composite significantly increased to 59.32 × 10⁶ S·m⁻1, a 7.83 % improvement over the pristine copper foil. This enhancement is attributed to the increased carrier density and mobility within the composite. These advancements suggest the potential of APCVD-grown graphene for various high-performance electronic applications, providing a promising pathway for further development and optimization of graphene-copper composites.

Dendrite Growth in Single-Grain and Cyclic-Twinned Sn–3Ag–0.5Cu Solder Joints

The microstructure of electronic solder joints is generated by the solidification of a small volume of bulk undercooled liquid. Here, we study β-Sn dendrite growth in Sn–3Ag–0.5Cu in the specific geometry and nucleation conditions of ball grid array (BGA) solder joints by combining electron backscatter diffraction and imaging of microstructures. It is shown that, while ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} is the preferred dendrite growth direction, out-of-plane branching and growth with ⟨11W⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 11W\\rangle$$\\end{document} directions are important for allowing dendrites to fan out into the spheroidal volume of BGA joints due to the low symmetry of β-Sn. We find that the crystallographic orientation of β-Sn at the nucleation point plays a strong role in subsequent dendrite growth. In single-grain joints, dendrites are often unfavorably oriented for growth, resulting in different types of zig-zag dendrite growth. In cyclic-twinned joints, it is shown how competitive out-of-plane trunk growth between three dendrite orientations produces {101} boundaries and the characteristic beachball microstructure.

Interdependence of Support Wettability ‐Electrodeposition Rate ‐ Sodium Metal Anode and SEI Microstructure

This study examines how current collector support chemistry (sodiophilic intermetallic Na2Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm‐2, 0.5‐3 mA cm‐2) representative of commercially relevant mass loading in anode‐free sodium metal battery (AF‐SMBs) are analyzed. Synchrotron X‐ray nanotomography and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) are combined with cryogenic focused ion beam (cryo‐FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te‐Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modelling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability.

In-situ self-catalyzed fabricating carbon nanotubes on [010] preferential LiMn0.5Fe0.5PO4 nanoplates to achieve excellent high rate performance

Nano carbon material composites significantly enhance the performance of lithium manganese iron phosphate (LMFP) cathode materials. This study investigates the self-catalytic growth mechanism of highly conductive carbon nanotubes (CNTs) on bare LMFP particles via chemical vapor deposition (CVD), focusing on the influence of particle size and crystallographic orientation. It is found that the Fe3C particles formed on static solvothermal synthesized LMFP nanoplates with high [010] orientation were effective to catalyze the generation of CNTs. Diverse CVD durations produced CNTs coatings with varying structures to impact electrochemical properties of final products. The MP-L/CNTs-2 sample, with 3.6 wt% carbon, showed the highest reversible capacity of 158 mAh g−1 at 1 C with 99.3 % capacity retention after 400 cycles, after 3000 cycles at 10 C, the retention rate was 74.5 %. In contrast, LMFP synthesized via solid-phase method (MP-S/C) only formed a carbon film on the surface and delivered 143 mAh g−1 at 1 C (97.6 % retention after 400 cycles) with prominent capacity loss at 10 C. This study provides new insights into the self-catalytic growth mechanism of CNTs to promote ion-electron conductivity and structural stability of LMFP materials, thus improving kinetic property and cycling stability for high-performance lithium-ion batteries.

Deformation and melt–rock interaction in the upper mantle: Insights from the layered structure of the Horoman peridotite, Japan

To obtain a better understanding of melt–rock interactions in the upper mantle, microstructural and petrological analyses were conducted on deformed mantle peridotites from the Horoman peridotite complex, Hokkaido, Japan. The Horoman peridotite complex is lithologically heterogeneous and contains various kinds of ultramafic and mafic rocks. We studied an outcrop of 3 × 70 m in size that contains layered spinel harzburgite, plagioclase lherzolite, and mafic rocks. The results indicate that reactive melts migrated preferentially along the foliation in the already deformed peridotite, and that these melt-rich zones became especially prone to further deformation. This inference is supported by (1) the parallelism of the boundaries of rock layers and foliation in the deformed peridotite, and the shape and crystallographic preferred orientations (SPOs and CPOs) of olivine in the peridotites; (2) the diffusive trends of magnesium and modal compositions of pargasite grains near the boundaries between peridotite and mafic layers; (3) variations in the NiO content of olivine crystals; (4) variations in olivine CPOs with orthorhombic (010)[100] slip system patterns and weak fiber-[010] patterns; and (5) the strong pargasite SPOs, the cuspate shapes of the pargasites, and the absence of intercrystallite deformation. The results, combined with previously reported P–T conditions for the Horoman peridotite complex, indicate that the deformed peridotites and mafic rocks with a layered structure represent temperatures of 1050–1150 °C and pressures of 0.7–1.5 GPa. Our results suggest that a decrease in pressure led to the transition from a melt-free to a melt-bearing system with a consequent change in the deformation mechanism, from dislocation creep in the melt-free system to diffusion creep in the melt-bearing system, with strain localization in the fine-grained melt-rich layers. The change in deformation mechanism is likely to have occurred in the uppermost mantle beneath a mid-ocean ridge, where strong rheological contrasts are controlled by spatial variations in the melt fraction.

The effect of pre-strain on textures, nano-twins and mechanical properties of a novel Nickel-based superalloy GH4251 with low stacking fault energy

By means of appropriate cold rolling pre-deformation, the tensile strength and plasticity of a novel polycrystalline precipitation-strengthened Nickel-based superalloy with low-stacking fault energy at 750 °C can be enhanced. The findings indicate that such pre-deformation leads to the emergence of microscopic substructures, including dislocations, anti-phase boundaries (APBs), stacking faults, and Lomer-Cottrell Locks (L-C locks). It is observed that the presence of these substructures is increased with the degree of pre-deformation. At the 15 % pre-deformation, a few deformation twins are detected near the grain boundaries, and their occurrence rises further in specimens subjected to 25 % pre-deformation. In addition, the nano-twins formation presents a strong correlation with the intensification of Brass-type textures. Notably, after the cold rolling pre-deformation, the alloy's yield strength as well as tensile strength at 750 °C is enhanced in contrast to those without pre-deformation, which is attributed to plentiful factors, such as low recovery and recrystallization activation energy, high-density nano-twins, grain refinement, and conducive crystallographic orientation for nano-twin mechanism activation caused by cold rolling pre-deformation. The specimen with 25 % pre-deformation exhibits relatively high tensile ductility. In this study, the relationships between pre-cold rolling deformation, microstructure, texture, and mechanical properties are comprehensively explored, indicating that the cold rolling pre-deformation holds promise for enhancing Nickel-based superalloys' strength and plasticity.

Concurrent dramatic enhancement of high-temperature strength and ductility in a high-entropy alloy via chain-like dual-carbides at grain boundaries

Grain boundaries (GBs) are often known as intergranular cracking sources in alloys at high temperatures, resulting in limited high-temperature strength and ductility. Here, we propose a GB-dual-carbide (denoted as GB-DC) strengthening strategy and have developed a high-performance (NiCoFeCr)99Nb0.5C0.5 high-entropy alloy (HEA) with exceptional strength-ductility synergy at 1073 K. Chain-like coherent M23C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic (FCC) matrix during deformation. Nano-scale NbC particles are distributed alternatively between M23C6 carbides and inhibit their coarsening. Both strength and ductility of the GB-DC HEA increase dramatically at strain rates ranging from 10−4 to 10−2 s−1 at 1073 K, compared with those of the single-phase NiCoFeCr HEA. Specifically, yield strength of 142 MPa, ultimate tensile strength of 283 MPa, and elongation of 34 % were obtained, which are twice that of the reference NiCoFeCr HEA (82 MPa, 172 MPa, and 18 %, respectively). EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature, and TEM analysis revealed that dislocations can go through the coherent phase boundaries (CPBs) and activate dipoles inner M23C6 carbides, which weakened the stress concentration in GBs. This substantially reduces the critical stress for dislocation generation and transmission to a stress level lower than that required for intergranular fracture. Theoretical estimation suggests that carbides result in a much higher activation energy (∼510 kJ/mol) for GB sliding and a rather low interface energy (∼101 mJ/m2) compared with the GB energy (1000 mJ/m2), which rationalizes the enhanced GB cohesion by carbides.

A comparative study of optical property on unintentionally doped and Sn-Doped β-Ga2O3 crystals by EFG method with a cylindrical Ir die

In this work, we carried out a comparative study of optical property on unintentionally doped and Sn-doped β-Ga2O3 crystals by edge-defined film-fed growth (EFG) method with a cylindrical iridium (Ir) die. The non-polarized Raman spectra showed the anisotropy in Raman peak position and intensity for three different planes (i.e., (100), (010) and (001)) of β-Ga2O3 crystals, independent of the Sn dopant. A difference in the Raman spectra between the unintentionally doped and Sn-doped β-Ga2O3 crystals was observed in the (001) plane. The strong in-plane anisotropy of the monoclinic β-Ga2O3 crystal related to the crystallographic orientation was demonstrated by the angle-resolved polarized Raman spectroscopy. The Sn dopant cannot change the optical transmittance and bandgap values of the unintentionally doped and Sn-doped β-Ga2O3 crystals with the (100), (010) and (001) orientations. However, the Sn-doped β-Ga2O3 crystal with the (010) orientation showed the higher valence band maximum and lower surface barrier height values. The X-ray photoelectron spectroscopy of the unintentionally doped and Sn-doped β-Ga2O3 crystals with the (010) orientation was also measured, which showed no obvious difference. The different luminescence centers and level of electron ionization of the unintentionally doped and Sn-doped β-Ga2O3 crystals were observed by the cathodoluminescence spectroscopy and electron paramagnetic resonance, respectively. Based on the comprehensive comparison, it can be concluded that the anisotropy in optical property of the unintentionally doped and Sn-doped β-Ga2O3 crystals with (100), (010) and (001) orientations apparently exist.

Deconstructing the Retained Austenite Stability: In Situ Observations on the Austenite Stability in One- and Two-Phase Bulk Microstructures During Uniaxial Tensile Tests

Given the critical role that metastable retained austenite (RA) plays in advanced high-strength steel (AHSS), there is significant interest in obtaining a comprehensive understanding of its stability, to achieve excellent mechanical properties. Despite considerable attention and numerous studies, the significance of individual contributions of various microstructural factors (size, crystallographic orientation, surrounding phases, etc.) on the stability of RA remain unclear, partly due to the difficulty of isolating the direct effects of these factors. In this study, we examined the influence of microstructural factors while minimizing the effect of chemical composition on the mechanical stability of RA. We accomplished this by comparing the austenite (γ) stability in two distinct microstructures: a two-phase RA/martensite microstructure and a one-phase γ microstructure, both with nearly identical γ compositions. We employed in situ high-energy X-ray diffraction during uniaxial tensile testing conducted at both room temperature and 100 °C, facilitating the continuous monitoring of microstructural changes during the deformation process. By establishing a direct correlation between the macroscopic tensile load, phase load partitioning, and the γ/RA transformation, we aimed to understand the significance of the microstructural factors on the mechanical stability of the RA. The results indicate that very fine RA size and the surrounding hard martensitic matrix (aside from contributing to load partitioning) contribute less significantly to RA stability during deformation than expected. The findings of this study emphasize the critical and distinct influence of microstructure on γ/RA stability.

Theoretical and experimental study of plasmon oscillation dispersion in Si and Ge crystals

Plasma fluctuation dispersion has been theoretically and experimentally studied in monocrystal samples of Si (111) and Ge (111). It has been shown that the dispersion depends on crystallographic orientations of materials under study. In this work, the dispersion effects in the CLEE spectra, which manifest themselves in bulk samples of Si and Ge, have been studied. The loss energy electron was studied by the CLEE method upon their reflection from Si(111) and Ge(111) at different angles of incidence of the electron beam on the surface. Calculation of the total electron energy loss with formula (5) shows that the form of the CLEE spectrum of primary electrons depends on the nature and magnitude of the electron density in a given direction and is in satisfactory agreement with the experimental data. Thus, the theoretical and experimental results show that in the case of single-crystalline Si and Ge, with increasing k, the values of the bulk plasma oscillation increase by 2–3 eV.

Enclaves as mushy magma strain archives: New perspectives on composite magmatic fabrics in plutons

Mineral fabrics within igneous intrusions can archive both tectonic and magmatic processes. However, whether magmatic state fabrics reflect primary magmatic processes or regional tectonic strain is often ambiguous. To investigate when fabrics are formed, one can compare the mineral fabrics to primary magmatic features, such as the interface between solidified magmas in mingling zones. The monzodioritic Fanad pluton shows a NNE-SSW–aligned petrofabric parallel to the strike of a nearby shear zone, with dioritic enclaves aligned parallel and oblique to this petrofabric. We therefore aimed to test if the enclaves’ internal fabrics are passive and align with enclave morphology or result from progressive overprint by regional tectonic strain. Crystallographic preferred orientation and anisotropy of magnetic susceptibility data from all enclaves and the host monzodiorite revealed a NNE-SSW petrofabric parallel to the regional tectonomagmatic fabric. However, anisotropy of anhysteretic remanent magnetization data within petrofabric-oblique enclaves revealed a primary fabric parallel to the enclave long axis. Therefore, we interpret enclave morphologies to reflect earlier magmatic state deformation, with fabrics being realigned to regional tectonic deformation. These two distinct petrofabrics were interpreted in the context of the magmatic processes and the evolving late Caledonian paleostress field, with earlier magma processes distinguished from subsequent tectonic overprinting occurring in the magmatic state. Our new data show that multiple fabrics are preserved within enclaves even though all fabric development occurred within a magmatic state. Our results also show that enclaves can effectively record successive strain events, providing new insight with which to decipher tectonomagmatic processes.

Shape Anisotropy of Grains Formed by Laser Melting of (CoCuFeZr)17Sm2

For permanent magnetic materials, anisotropic microstructures are crucial for maximizing remanence Jr and maximum energy product (BH)max. This also applies to additive manufacturing processes such as laser powder bed fusion (PBF-LB). In PBF-LB processing, the solidification behavior is determined by the crystal structure of the material, the substrate, and the melt-pool morphology, resulting from the laser power PL and scanning speed vs. To study the impact of these parameters on the textured growth of grains in the melt-pool, experiments were conducted using single laser tracks on (CoCuFeZr)17Sm2 sintered magnets. A method was developed to quantify this grain shape anisotropy from electron backscatter diffraction (EBSD) analysis. For all grains in the melt-pool, the grain shape aspect ratio (GSAR) is calculated to distinguish columnar (GSAR < 0.5) and equiaxed (GSAR > 0.5) grains. For columnar grains, the grain shape orientation (GSO) is determined. The GSO represents the preferred growth direction of each grain. This method can also be used to reconstruct the temperature gradients present during solidification in the melt-pool. A dependence of the melt-pool aspect ratio (depth/width) on energy input was observed, where increasing energy input (increasing PL, decreasing vs) led to higher aspect ratios. For aspect ratios around 0.3, an optimum for directional columnar growth (93% area fraction) with predominantly vertical growth direction (mean angular deviation of 23.1° from vertical) was observed. The resulting crystallographic orientation is beyond the scope of this publication and will be investigated in future work.

Atomistic insight into laser shock peening response of α-titanium: an experimentally verified simulation study

Laser shock peening (LSP) can induce severe plastic deformation in the surface zone of metallic materials, which potentially enhances their mechanical properties. Although it is widely recognized that the improvement of mechanical properties can be attributed to microstructure evolution, the microstructural characteristics and response under different LSP parameters are complex, leading to distinct mechanical behaviors of materials at the macroscale. Besides, the exceedingly brief duration of LSP also poses considerable challenges to capture the microstructure evolution within the surface layer of materials. Therefore, to grasp a first in-situ atomistic insight into LSP response of α-titanium, molecular dynamics method is applied to simulate laser incidence at the [101¯0] crystallographic orientation with various energy densities. The results show that the lattice reorientation and dislocation slip dominate the plastic deformation at low laser energy density, while stacking faults and crystal disordering are the primary microstructural features at high laser energy density. The above shock-induced microstructures are verified by transmission electron microscopy (TEM) observations. Further, varied microscale plastic deformation modes under varying shock energies are proposed based on Schmid factors and energy barriers. The findings bridge laser energy to post-processing microstructure of α-titanium, which paves the way for improving mechanical properties of materials by optimizing LSP treatment parameters.

Effect of the crystallographic orientation of the surface of single-crystal Si wafers on the endotaxial growth of NiSi2 nanoplates

A multi-technique analysis was used to investigate how the orientation of single-crystal Si wafer surfaces affects the size, shape and orientation of NiSi2 nanocrystals grown within the wafers through the thermal diffusion of Ni atoms from a nickel-doped thin film deposited on the surface. Nickel-doped thin films were prepared on silicon wafers with three distinct crystallographic orientations, [001], [110] and [111]. Three sets of samples were then annealed at 500, 600 and 700°C for 2 h. Regardless of crystallographic orientation or annealing temperature, NiSi2 nanoplates with a nearly hexagonal shape grew close to the external surface of the wafers, aligning their larger surfaces parallel to one of the planes of the Si{111} crystallographic form. The crystallographic orientation and annealing temperature in the 500–700°C range did not significantly affect the final values of the average diameter and thickness of the nanoplates. However, significant differences were noted in the number of nanoplates formed in Si wafers with different crystallographic orientations. The results indicate that these observed differences are correlated with the number of pre-existing defects in the wafers that influence the heterogeneous nucleation process. In addition, the average size and size dispersion were determined for pores at the surface of the Si wafers formed due to the etching process used for native oxide removal.

Crystallographic orientation dependence in creep deformation of micron-thick silicon films for 3-D microstructures

In this study, the steady-state creep deformation properties of 5 μm-thick single crystal silicon (Si) films at elevated temperatures were investigated using punch creep-forming tests for the design of three-dimensional (3-D) microstructured MEMS. The relationship between the creep strain rate and stress of the Si films with {100}, {110}, and {111} planes at temperatures of 1223–1323 K was derived using finite element analysis following punch creep-forming tests, and a power-law creep constitutive equation for Si films was determined. The steady-state creep properties of the Si film samples varied clearly with crystallographic orientations. Among the three crystallographic orientations, the creep strain rate of the micron-thick Si films was the fastest for the {011} plane, followed by the {111} and {001} planes, in the applied stress range of 110 MPa to 220 MPa. This is consistent with the increasing order of magnitude of the thermal activation energy. The crystallographic orientation dependence of the steady-state creep properties of Si films is discussed based on the mobility of dislocation gliding per unit lattice and scanning electron microscope observations. The sample-size dependence of the creep strain rate of Si with the {001} plane was clearly observed between the micron- and millimeter-thick samples, which was attributed to the difference in the frequency factor of the power-law creep. However, the thermal-activation energy remained constant. This study successfully revealed the steady-state creep properties of Si films and provided useful engineering data for the design of 3-D Si-MEMS fabrication by the plastic processing of Si films.

Recrystallization of deformed metal nanoparticles

Despite great advances in the fabrication methods of metal nanoparticles with various sizes and shapes, the available tools for manipulating their microstructure and morphology still remain limited. In the present work we introduce the age-old metallurgical technique of recrystallization to the synthesis of metallic nanoparticles. We uniaxially compressed a large number of single crystalline and defect free Pt nanoparticles obtained by solid-state dewetting and annealed them at the temperature of 1000 °C. Our findings reveal that, while the as-dewetted particles exhibited similar shapes and crystallographic orientations, the plastic deformation and annealing led to a diverse range of shapes, microstructures, and orientations among the particles. We categorized the particles into four distinct types based on their appearance: slanted, terraced, “Danish pastry”, and broken particles. Finally, we propose a differentiation mechanism responsible for this diversification, which relies on a combination of recrystallization, surface step formation, and solid-state dewetting processes.

Orientation-dependent electronic structure in interfacial superconductors LaAlO3/KTaO3

Emergent superconductivity at the LaAlO3/KTaO3 interfaces exhibits a mysterious dependence on the KTaO3 crystallographic orientations. Here by soft X-ray angle-resolved photoemission spectroscopy, we directly resolve the electronic structure of the LaAlO3/KTaO3 interfacial superconductors and the non-superconducting counterpart. We find that the mobile electrons that contribute to the interfacial superconductivity show strong k⊥ dispersion. Comparing the superconducting and non-superconducting interfaces, the quasi-three-dimensional electron gas with over 5.5 nm spatial distribution ubiquitously exists and shows similar orbital occupations. The signature of electron-phonon coupling is observed and intriguingly dependent on the interfacial orientations. Remarkably, the stronger electron-phonon coupling signature correlates with the higher superconducting transition temperature. Our observations help scrutinize the theories on the orientation-dependent superconductivity and offer a plausible and straightforward explanation. The interfacial orientation effect that can modify the electron-phonon coupling strength over several nanometers sheds light on the applications of oxide interfaces in general.

Polarized Upconversion of sub-100 nm Single Nanoparticles.

Upconversion nanoparticles are popular as imaging probes due to their advantages in photostability and controllable emission dimensions. However, upconversion polarization remains largely uncharted with previous reports limited to microstructures. In this work, we report the observation of polarized upconversion emissions from β-NaYF4 single nanostructures below 100 nm. At the sub-100 nm scale, nanorods, nanodiscs, and nanoplates exhibit distinctive polarization degrees despite the same doping concentrations of lanthanides. We find this varied polarization degree results from the crystallographic orientation of nanostructure in relation to the light field and can be linked to the distinctive emission spectrum profile with varied Stark splitting transition ratios from Er3+. Our findings provide a comprehensive understanding of the polarization properties of upconversion nanoparticles, revealing a previously unexplored aspect of light emission. This discovery expands our knowledge of upconversion nanoparticles and also opens new possibilities for their use in future imaging and sensing applications, where polarization sensitivity is crucial.

Effect of crystallographic orientation on mechanical properties of Al0.25CoCrFeNi high entropy alloy under tension

The deformation behavior of single-crystal materials is closely related to the crystallographic orientation. However, there are few simulations and experimental studies on the effect of crystallographic orientation on the tensile properties of single-crystal AlxCoCrFeNi high entropy alloys (HEAs). Molecular dynamics simulations were used to analyze the mechanical properties and structural variations of Al0.25CoCrFeNi HEAs with different crystallographic orientations under tension. Prior to yielding, elastic softening occurred in [111], [110] and [11̅0]-oriented HEAs, except for [100]-oriented HEA. During plastic deformation, [100]-oriented HEA had high strength and flow stress due to the low Schmid factors of leading partial dislocations and multiple activatable slip systems. [111]-oriented HEA also showed high strength and flow stress, which were attributed to the low Schmid factors of the activatable slip systems and the existence of incomplete stacking fault tetrahedrons. Both [110]- and [11̅0]-oriented HEAs showed low strength, but the presence of the secondary increased stress suggested they had good plasticity. The difference between them was that [110]-oriented HEA was easier to form hexagonal close-packed lamellae and experienced secondary yielding at larger strain. This suggested that different crystallographic orientations in the non-tensile direction also affected the mechanical properties.

Influence of textural variability on plastic response of porous crystal embedded in polycrystalline aggregate: A crystal plasticity study

Damage evolution in polycrystalline aggregates is complicated by the intricate interplay of crystallographic orientation of the porous grain and the surrounding anisotropic matrix. Therefore, formulation of design rules and damage models for polycrystalline materials proves daunting due to relative lack of thorough understanding of the underlying heterogeneity at the mesoscale. This work explores the orientation dependent void growth in a porous crystal embedded in an anisotropic polycrystalline matrix with different initial textures. Polycrystalline face-centered cubic based aggregate is simulated within the framework of crystal plasticity finite element method. Porosity is first modeled in the form of a single pre-existing spherical void in the central grain of the randomly oriented polycrystal. One-hundred crystallographic orientations of the central grain in three-dimensional Euler space are analyzed to reveal the orientation dependent trends of the porous grain. To account for textural variability, the analysis is repeated for polycrystals exhibiting preferred textures like Cube, Brass, Copper and Goss. In this manner, interesting orientation dependent trends in basic tenets of void growth like yield strength, coalescence strain and porosity evolution are unraveled across various polycrystalline textures. To account for spatial heterogeneity as well, porosity in the central grain is then re-distributed and the aforementioned analysis is repeated for all the crystallographic orientations of the central grain embedded in polycrystals with different textures. Owing to the large amount of data thus generated, statistical analysis is invoked to identify stimulating trends and key statistical variables governing the strength and toughness. Consequently, a statistical void growth model is also presented by assessing the CP simulation results and identifying suitable distribution function governing the growth of voids in polycrystals. The modeling framework is expected to inform porous plasticity models aimed at capturing damage evolution in porous grains embedded in polycrystalline materials exhibiting topological and crystallographic anisotropy.