Differences In Grain Morphology Research Articles

Perspective on High-Stability Single-Crystal Li-Rich Cathode Materials for Li-Ion Batteries.

Benefiting from anionic and cationic redox reactions, Li-rich materials have been regarded as next-generation cathodes to overcome the bottleneck of energy density. However, they always suffer from cracking of polycrystalline (PC) secondary particles and lattice oxygen release, resulting in severe structural deterioration and capacity decay upon cycling. Single-crystal (SC) design has been proven as an effective strategy to relieve these issues in traditional Li-rich cathodes with PC morphology. Herein, we first reviewed the main synthesis routes of SC Li-rich materials including solid-state reaction, molten salt-assisted, and hydrothermal/solvothermal methods, in which the differences in grain morphology, electrochemical behaviors, and other properties induced by various routes were analyzed and discussed. Furthermore, the distinct characteristics were compared between SC and PC cathodes from the aspects of irreversible capacity, structural stability, capacity/voltage degradation, and gas release. Besides, recent advances in layered SC Li-rich oxide cathodes were summarized in detail, where the unique structural designs and modification strategies could greatly promote their structural/electrochemical stability. At last, challenges and perspectives for the emerging SC Li-rich cathodes were proposed, which provided an exceptional opportunity to achieve high-energy-density and high-stability Li-ion/metal batteries.

Al-Co-Cr-Fe-Ni high-entropy coatings produced by non-vacuum electron beam cladding: Understanding the effect of Al by in-situ synchrotron X-ray diffraction

This study investigates the structure and properties of Al-Co-Cr-Fe-Ni high-entropy alloy (HEA) based coatings on steel substrates produced by non-vacuum electron beam cladding. Powder mixtures with Al molar ratios of 0.5, 1, and 1.5 were used for cladding, resulting in coatings with fcc, bcc + fcc, and bcc structures, respectively. The Fe content, which entered the coating from the substrate during cladding, increased from 9.9 up to 48.1 at. %. with the decrease of the Al molar fraction from 1.5 to 0.5. In-situ synchrotron X-ray diffraction analysis showed that this effect can be attributed to the higher solidus temperatures of the compositions with higher Al content. Electron backscatter diffraction showed that differences in grain morphology and crystallographic texture were related to the crystallization temperatures in different zones of the coatings. The bcc coating with an Al molar ratio of 1.5 demonstrated superior hardness and wear resistance. Fcc coating, which received more Fe from the substrate, had lower hardness and was prone to plastic flow. However, the specific wear rate of the fcc coating was close to that of the bcc + fcc one due to the hardening of the fcc phase during sliding wear.

Structural evolution of HMX during processing operations

ABSTRACT The impact of processing operations such as chemical synthesis conditions, milling, coating and pressing operations on the crystallographic structure of HMX has been studied using X-ray diffraction and Rietveld analysis. Strong differences in grain morphology and X-ray patterns were first observed after synthesis on two different setups with different washing methods. Diffraction pattern refinements were tentatively performed on the basis of known structures and assuming preferential orientations. The impossibility of achieving satisfactory agreement, even considering the orientation of several planes, could be attributed to the presence of polymorphism or hydrates. The possible new polymorphs or hydrates were metastable since milling led to the stable ß-HMX polymorph. No such transformation occurred during the coating operation, but an increase in structural defects was observed. Finally, the pressing step did not induce any transformation but surprisingly led to a decrease in structural defects, probably due to isotropic deformation of the crystallographic cell and the repairing effect of the associated thermal treatment.

Grain boundary deformation in uniaxial strained Nb3Sn

We generated a three-dimensional stress map of grains and grain boundaries in uniaxial strained Nb3Sn composite, using a scale-coupled model generated by the polycrystalline finite element method and based on the linear elastic theory of closely packed fiber-reinforced composites. The model takes into account the transfer of stress from a Cu-Sn matrix to a single Nb3Sn filament composed of inner elongated and outer equiaxed grains. Due to differences in grain morphology and orientation, stress inhomogeneity arises first in the filament. The interconnected grain boundary networks in Nb3Sn constrain grain deformation by fostering stress concentration at intersections between multiple grains. The degree of stress concentration can be as high as 2.08. Our model simulations show a random distribution of grain boundary orientations within stress concentration zones and provide detailed information on how and where stress inhomogeneity is likely to produce crack initiation in Nb3Sn.

Targeted mutation of barley (1,3;1,4)-β-glucan synthases reveals complex relationships between the storage and cell wall polysaccharide content.

Barley (Hordeum vulgare L) grain is comparatively rich in (1,3;1,4)-β-glucan, a source of fermentable dietary fibre that protects against various human health conditions. However, low grain (1,3;1,4)-β-glucan content is preferred for brewing and distilling. We took a reverse genetics approach, using CRISPR/Cas9 to generate mutations in members of the Cellulose synthase-like (Csl) gene superfamily that encode known (HvCslF6 and HvCslH1) and putative (HvCslF3 and HvCslF9) (1,3;1,4)-β-glucan synthases. Resultant mutations ranged from single amino acid (aa) substitutions to frameshift mutations causing premature stop codons, and led to specific differences in grain morphology, composition and (1,3;1,4)-β-glucan content. (1,3;1,4)-β-Glucan was absent in the grain of cslf6 knockout lines, whereas cslf9 knockout lines had similar (1,3;1,4)-β-glucan content to wild-type (WT). However, cslf9 mutants showed changes in the abundance of other cell-wall-related monosaccharides compared with WT. Thousand grain weight (TGW), grain length, width and surface area were altered in cslf6 knockouts, and to a lesser extent TGW in cslf9 knockouts. cslf3 and cslh1 mutants had no effect on grain (1,3;1,4)-β-glucan content. Our data indicate that multiple members of the CslF/H family fulfil important functions during grain development but, with the exception of HvCslF6, do not impact the abundance of (1,3;1,4)-β-glucan in mature grain.

Microstructural development in DED stainless steels: applying welding models to elucidate the impact of processing and alloy composition

Austenitic stainless steel microstructures produced by directed energy deposition (DED) are analogous to those developed during welding, particularly high energy density welding. To better understand microstructural development during DED, theories of microstructural evolution, which have been established to contextualize weld microstructures, are applied in this study to microstructural development in DED austenitic stainless steels. Phenomenological welding models that describe the development of oxide inclusions, compositional microsegregation, ferrite, matrix austenite grains, and dislocation substructures are utilized to clarify microstructural evolution during deposition of austenitic stainless steels. Two different alloys, 304L and 316L, are compared to demonstrate the broad applicability of this framework for understanding microstructural development during the DED process. Despite differences in grain morphology and solidification mode for these two alloys (which can be attributed to compositional differences), similar tensile properties are achieved. It is the fine-scale compositional segregation and dislocation structures that ultimately determine the strength of these materials. The evolution of microsegregation and dislocation structures is shown to be dependent on the rapid solidification and thermomechanical history of the DED processing method and not the composition of the starting material.

Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases

In this work, the microstructure, texture, phases, and microhardness of 45° printed (with respect to the build direction) homogenized, and hot isostatically pressed (HIP) cylindrical IN718 specimens are investigated. Phase morphology, grain size, microhardness, and crystallographic texture at the bottom of each specimen differ from those of the top due to changes in cooling rate. High cooling rates during the printing process generated a columnar grain structure parallel to the building direction in the as-printed condition with a texture transition from (001) orientation at the bottom of the specimen to (111) orientation towards the specimen top based on EBSD analysis. A mixed columnar and equiaxed grain structure associated with about a 15% reduction in texture is achieved after homogenization treatment. HIP treatment caused significant grain coarsening, and engendered equiaxed grains with an average diameter of 154.8 µm. These treatments promoted the growth of δ-phase (Ni3Nb) and MC-type brittle (Ti, Nb)C carbides at grain boundaries. Laves phase (Fe2Nb) was also observed in the as-printed and homogenized specimens. Ostwald ripening of (Ti, Nb)C carbides caused excessive grain growth at the bottom of the HIPed IN718 specimens, while smaller grains were observed at their top. Microhardness in the as-fabricated specimens was 236.9 HV and increased in the homogenized specimens by 19.3% to 282.6 HV due to more even distribution of secondary precipitates, and the nucleation of smaller grains. A 36.1% reduction in microhardness to 180.5 HV was found in the HIPed condition due to γ ″ phase dissolution and differences in grain morphology.

Prediction of grain structure evolution during rapid solidification of high energy density beam induced re-melting

Grain boundary migration in the presence of concentrated sources of heat is a complex process that has a considerable impact on resultant material properties. A phase field model is presented incorporating thermal gradient and curvature driving force terms to predict how a poly-crystalline network evolves due to the application of such heat sources, as grain boundaries migrate due to local boundary curvature and time-varying thermal gradients. Various thermal scenarios are investigated, in both two and three dimensions. These scenarios include both partial and full penetration laser induced melting, the application of a linearly varying time-independent thermal field, and successive melting events where regions experience multiple melting and solidification cycles. Comparisons are made between the microstructures predicted by the proposed phase field method, during the various thermal scenarios, that agree with commonly observed phenomena. Particularly interesting is the ability to explain the differences in grain morphology between the full penetration and partial penetration welds using the phase field model and associated driving force magnitudes between the two scenarios. The model predicts the restoration of grain boundary networks in regions experiencing multiple melting events, and explains the differences in grain morphology due to the local curvature and thermal gradient effects.

Microstructure and Properties of an Al-Zn-Mg-Cu Alloy Plate

The inhomogeneous microstructure and properties at typical position of an Al-7.7Zn -1.7Mg-1.4Cu-0.11Zr alloy plate in T7651 condition have been investigated using OM, TEM and EBSD analysis, tensile properties testing, conductivity measurement and fracture toughness testing. The results indicate that there are obvious differences in grain morphology, quench-introduced precipitation and recrystallization degree in the two typical positions of near the surface layer (T/8 plane) and in the center (T/2 plane) along the thickness direction of the plate. There appear some amount of quench-introduced precipitates at the T/2 plane of the alloy plate, which improves the electrical conductivity. And there is a higher proportion of the recrystallization organization at the T/2 plane of the alloy plate, seriously affecting its elongation and fracture toughness. Due to without marked characteristic of rolling flow line, the strength at the T/8 plane of the alloy plate is lower. The properties at T/8 plane and at T/2 plane of the alloy plate exhibit a difference of 3~18%. Microstructure inhomogeneity of the alloy plate determines the uniformity of its properties.

Properties and Microstructure of an Al-Zn-Mg-Cu Alloy Forging

In this study, the inhomogeneous properties and microstructure at typical position of an Al-7.5Zn-1.6Mg-1.4Cu-0.11Zr alloy forging in T7452 condition have been investigated using OM, SEM, TEM and EBSD analysis, tensile properties testing, conductivity measurement and fracture toughness testing. The results indicate that wherein the properties near the surface layer and in the core of the alloy forging exhibit a difference of 10% or more. There are obvious differences in grain morphology, quench-introduced precipitation and recrystallization degree in the two positions. Due to the high quenching temperature, there appears a heavy quench-introduced precipitation phenomenon in the core more than surface layer of the alloy forging, which improves the electrical conductivity, but significantly reduces the strength of the final material. And there is a higher proportion of the recrystallization organization in the core of the alloy forging, seriously affecting its elongation and fracture toughness. Microstructure inhomogeneity of the alloy forging determines the uniformity of its properties.

Microstructure and Properties of an Al-7.5Zn-1.5Mg-1.4Cu-0.12Zr Alloy Forging

In this present work, the microstructure and properties of an Al-7.5Zn-1.5Mg-1.4Cu-0.12Zr alloy forging in T7452 condition has been investigated by means of OM, TEM and EBSD analysis and varied properties test. The results indicate that there are obvious differences in grain morphology, precipitation characteristics and recrystallization degree along the thickness direction of the forging. The strength of the alloy forging is stable and varies less than 10% along the thickness direction. The alloy forging in the T7452 condition shows high strength, high toughness and good corrosion resistance, with the UTS, TYS, elongation and electrical conductivity values being 500~530 MPa, 460~500 MPa, 7.0~15.0% and 23.9~24.2 MS/m, respectively, and the fracture toughness in L-T, T-L and S-L direction being 33.5~39.5, 25.5~27.0, 23.0~24.5 MPa.m1/2, respectively, and the EXCO rating being EA.

High Temperature microhardness of hard coatings produced by physical and chemical vapor deposition

The microhardness of hard coatings of TiN and HfN prepared by chemical vapor deposition (CVD) and TiN, HfN, ZrN and TiAlN prepared by physical vapor deposition (PVD) were measured between room temperature and 1000°C. The microhardness of the PVD coatings was significantly higher than that of the CVD counterparts at room temperature but all microhardness values tended to converge at 1000°C. Higher N: Ti ratios were found in PVD TiN relative to CVD TiN. X-ray diffraction measurements indicated that the PVD coatings contained high residual compressive growth stresses associated with lattice distortion and very fine grain size, which were confirmed using transmission electron microscopy. Low residual stresses in high temperature CVD coatings are caused by thermal expansion mismatch between coating and substrate. Differences in grain morphology and crystal texture are attributed to varying conditions of energetic bombardment and deposition temperature in the several PVD methods employed. The faster decrease in microhardness with temperature in PVD coatings is caused by the high residual energy and finer grain size.