Diffraction Microstructure Research Articles

Breaking the strength-ductility trade-off in austenitic stainless steel at cryogenic temperatures: Mechanistic insights

At cryogenic temperatures, 316L austenitic stainless steel (ASS) exhibits remarkable strength while retaining high ductility, defying the conventional stress-strain trade-off. Despite extensive studies documenting the cryo-tensile properties of ASSs, the underlying mechanisms behind this phenomenon remain largely unexplored. This study systematically re-examines the tensile properties of 316L stainless steel and the associated mechanisms across a range of low temperatures (293 K, 223 K, 123 K, and 77 K). The reasons for the superior stress-strain balance (∼80 % GPa) are discussed using results from electron backscatter diffraction (EBSD) microstructure characteristics. The results undoubtedly suggest that the transformation mechanisms, specifically the shift from deformation twinning to martensitic transformation (γ → ε → α′), play a crucial role in enhancing elongation at cryogenic temperatures. At these temperatures, the Gibbs free energy difference between ε-martensite and γ-austenite approaches zero, resulting in slow martensite growth. The stress-strain curves at low temperatures satisfy the Considère criterion, indicating delayed necking under these conditions. This behavior is ascribed to the presence of various hierarchical microstructures, including ε, α′, γ-twins, ε-twins and their intersections, which act as sources of work hardening. This study provides new insights into deformation behavior of ASSs under cryogenic conditions.

Thermal conductivity prediction of Al[formula omitted]O[formula omitted]-doped tetragonal YSZ coatings using deep learning

Thermal barrier coatings, including Al2O3-doped tetragonal yttria-stabilized zirconia (t-YSZ) coatings are vital in diverse applications. Thermal conductivity is a key property, but prediction often requires some complex experiments. In this study, a novel dual-structure feature extraction coupled with a multi-scale attention fusion network (RCFNet) is introduced for accurate thermal conductivity prediction using electron backscattered diffraction (EBSD) microstructure images. The method requires minimal data, and the result shows high accuracy with a Mean Square Error (MSE) of 0.003 W(m⋅k)−1 and an R-squared (R2) value of 0.81. Furthermore, the model reveals specific correlations between microstructural characteristics and thermal conductivity, facilitating rapid structure selection for specific thermal conductivity.

Multiscale in-situ characterization of static recrystallization using dark-field X-ray microscopy and high-resolution X-ray diffraction

Dark-field X-ray microscopy (DFXM) is a high-resolution, X-ray-based diffraction microstructure imaging technique that uses an objective lens aligned with the diffracted beam to magnify a single Bragg reflection. DFXM can be used to spatially resolve local variations in elastic strain and orientation inside embedded crystals with high spatial (~ 60 nm) and angular (~ 0.001°) resolution. However, as with many high-resolution imaging techniques, there is a trade-off between resolution and field of view, and it is often desirable to enrich DFXM observations by combining it with a larger field-of-view technique. Here, we combine DFXM with high-resolution X-ray diffraction (HR-XRD) applied to an in-situ investigation of static recrystallization in an 80% hot-compressed Mg–3.2Zn–0.1Ca wt.% (ZX30) alloy. Using HR-XRD, we track the relative grain volume of > 8000 sub-surface grains during annealing in situ. Then, at several points during the annealing process, we “zoom in” to individual grains using DFXM. This combination of HR-XRD and DFXM enables multiscale characterization, used here to study why particular grains grow to consume a large volume fraction of the annealed microstructure. This technique pairing is particularly useful for small and/or highly deformed grains that are often difficult to resolve using more standard diffraction microstructure imaging techniques.

Competitive role of primary [formula omitted] precipitates and annealing twins on the heterogeneous deformation of a polycrystalline ni-based superalloy: Crystal plasticity modeling and experiments

A crystal plasticity modeling framework is developed and used in combination with experiments for studying the deformation behavior of a polycrystalline Ni-based superalloy. In particular, the monotonic stress-strain response across a range of temperatures and the misorientation development at room temperature are predicted. The model accounts for individual deformation of the matrix and primary γ′ phases, with consideration for the various strengthening mechanisms observed in these alloys. The as-received microstructure has been characterized using Energy Dispersive X-Ray Spectroscopy (EDS) and the concentration of the solute atoms present in the γ and primary γ′ phases obtained from these measurements are used to inform the solute solution strengthening model. Further, the Electron Back Scatter Diffraction (EBSD) microstructures are directly used as inputs for the simulations. The model is first calibrated to the experimental stress-strain response at 293 K and 923 K and then validated by predicting the mechanical response at 523 K and 723 K. Interrupted tensile testing has been performed using a combination of Scanning Electron Microscopy (SEM) and EBSD to study the misorientation developments during deformation. These deformed microstructures are correlated with the simulated EBSD microstructures, in terms of the competitive misorientation developments at grain boundaries, annealing twin boundaries and phase interfaces. Higher misorientation developments were observed at the twin boundaries as compared to the grain boundaries and phase interfaces, indicating a higher propensity of heterogeneous deformation.

Hot Deformation Behavior and Dynamic Softening Mechanism in 7B50 Aluminum Alloy.

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320-460 °C/0.001-1.0 s-1. According to the flow curves obtained from the experiments, the flow behavior of this alloy was analyzed, and the Zener-Hollomon (Z) parameter equation was established. The hot processing maps of this alloy were developed based on the dynamic material model, and the optimal hot working region was determined to be 410-460 °C/0.01-0.001 s-1. The electron backscattered diffraction (EBSD) microstructure analysis of the deformed sample shows that the dynamic softening mechanism and microstructure evolution strongly depend on the Z parameter. Meanwhile, a correlation between the dynamic softening mechanism and the lnZ value was established. Dynamic recovery (DRV) was the only softening mechanism during isothermal compression with lnZ ≥ 20. Discontinuous dynamic recrystallization (DDRX) becomes the dominant dynamic recrystallization (DRX) mechanism under deformation conditions of 15 < lnZ < 20. Meanwhile, the size and percentage of DDRXed grains increased with decreasing lnZ values. The geometric dynamic recrystallization (GDRX) mechanism and continuous dynamic recrystallization (CDRX) mechanism coexist under deformation conditions with lnZ ≤ 15.

Formula omitted]-CP: Open source dislocation density based crystal plasticity framework for simulating temperature- and strain rate-dependent deformation

This work presents an open source, dislocation density based crystal plasticity modeling framework, ρ-CP. A Kocks-type thermally activated flow is used for accounting for the temperature and strain rate effects on the crystallographic shearing rate. Slip system-level mobile and immobile dislocation densities, as well slip system-level backstress, are used as internal state variables for representing the substructure evolution during plastic deformation. A fully implicit numerical integration scheme is presented for the time integration of the finite deformation plasticity model. The framework is implemented and integrated with the open source finite element solver, Multiphysics Object-Oriented Simulation Environment (MOOSE). Example applications of the model are demonstrated for predicting the anisotropic mechanical response of single and polycrystalline hcp magnesium, strain rate effects and cyclic deformation of polycrystalline fcc OFHC copper, and temperature and strain rate effects on the deformation of polycrystalline bcc tantalum. Simulations of realistic Voronoi-tessellated microstructures as well as Electron Back Scatter Diffraction (EBSD) microstructures are demonstrated to highlight the model’s ability to predict large deformation and misorientation development during plastic deformation.

Correlation between dislocation hardening and the geometrically-necessary-dislocation densities in a hexagonal-close-packed Zr-2wt%Ti alloy

Geometrically necessary bands (GNBs) that are reflected by variations in the geometrically necessary dislocation densities (GNDDs) often appear at early stages of deformation. Studying the hardening variation inside and outside of GNBs is helpful for understanding how GNBs are formed to accommodate deformation heterogeneity. The former requires an accurate estimation of the slip activities at the mesoscale. Making use of the facts that the lattice rotation induced by prismatic <a> slips does not affect the <0001> direction, and one resulting from basal <a> slips does not influence an axis ⊥ <0001>, the slip activities identified by both the crystal plasticity model and slip traces for the electron backscatter diffraction microstructures after compression were verified. An abundance of GNBs was observed. The hardening/softening effect in the GNBs is always compensated by a softening/hardening behavior near the GNBs. Such microstructural features are also reflected in the profiles of frequency as a function of strength for both high and low GNDD regions: they share the same shape and peak positions. This confirms that the high GNDD region is always accompanied by a low GNDD region, and the GNDDs are independent of grain strength. Strong dependence of slip activities on grain orientations was identified, while the GNDDs are independent of orientations. The present paper provides experimental evidences of the identified slip activities and a way to explore the correlation between dislocation hardening and the GNDDs.

Highly Efficient Double-Layer Diffraction Microstructures Based on New Plastics and Molded Glasses

Within the framework of rigorous diffraction theory, the maximum possible incidence angles of radiation on two-layer sawtooth relief-phase microstructures in the visible (0.4 ≤ λ ≤ 0.7 μm) spectral range are compared. Optical materials for the layers of these microstructures are selected from a database of 47 plastics and 165 molded glasses. It is shown that when the ratio of the spatial period of the microstructure to the effective depth of the relief is greater than 20, the achievable angles within which the diffraction efficiency exceeds 0.95 lie in a wide range from 18.5° to 40.5° for single-relief structures and 7.5° to 22.3° for structures with two internal reliefs. The best results for purely plastic microstructures are obtained when the plastic CMT and the indium tin oxide nanocomposite in polymethylmethacrylate are used.

Limiting spectral and angular characteristics of sawtooth dual-relief two-layer diffraction microstructures

Sawtooth two-layer microstructures with internal and external, as well as with two internal reliefs, composed of technological and commercially available optical plastics or an optical plastic and nanocomposite material are investigated. By using the corresponding model microstructures in the frameworks of the rigorous diffraction theory, the limiting spectral and angular characteristics are estimated for sawtooth two-layer dual-relief diffraction microstructures of both types.

The Structural and Thermodynamic Analysis of Phase Formation Processes in Equiatomic AlCoCuFeNiCr High-Entropy Alloys

Phase formation processes in equiatomic AlCoCuFeNiCr high-entropy alloys have been studied by means of x-ray diffraction method, microstructure analysis and microhardness measurements. Thermodynamic and structural criteria for predicting the phase composition of the alloys were considered. It is shown that in AlCoCuFe, AlCoCuFeNi and AlCoCuFeNiCr alloys the two-phase mixture of solid solutions on the base of the BCC and FCC lattices is formed. With a decrease in the fraction of Al atoms, the tendency to disordering of BCC solid solution occurs. It was also established that alloys under investigation reveal a dendritic structure in which Cu-enriched FCC phase is deposited in the regions between the dendrites of the main BCC phase. The correlation between microhardness of the alloys and volume fractions of phase constituents and their thermodynamic characteristics are revealed.

Potential opportunities of sawtooth diffraction microstructure with two layers and single relief

We present the estimated parameter (Q factor) derived from scalar diffraction theory for a two-layer single-relief sawtooth diffraction microstructure comprising a pair of optical materials. The Q factor allows the negative effects that arise due to the nonlinearity of the difference in the refractive indices of optical materials to be evaluated. This parameter enables pairs of optical materials to be easily compared and the most promising ones to be selected. Using the mathematical model based on microstructures with the minimum and maximum Q factor values, the best possible angular characteristics in framework of the rigorous theory of diffraction are estimated for a two-layer single-relief microstructure. It is shown that the angular characteristics of a microstructure composed of two nanocomposite materials are very close to the maximum possible characteristics.

Limiting spectral and angular characteristics of multilayer relief – phase diffraction microstructures

Methods for estimating the parameters of relief – phase diffraction microstructures (local and integral Q-factors) are extended to the case of multilayer double-relief sawtooth microstructures, which makes it possible to select the best combinations of optical materials for multilayer microstructures at a very low computational burden. An approach to the study of multilayer microstructures is proposed, based on the combined use of Q-factors and the method of rigorous analysis of coupled waves, which allows one to estimate the limiting spectral and angular characteristics of multilayer microstructures of various types.

Small-angle X-ray powder diffraction analyses, microstructure and morphology of some synthesized template silica samples related to the 2-methoxyethanol content

Small-angle X-ray powder diffraction analyses, microstructure and morphology of some synthesized template silica samples related to the 2-methoxyethanol content

The microstructure of low carbon microalloyed steel and impact toughness scattering during fracture in ductile-to-brittle transition region

The connection between occurrence of remarkable impact toughness scattering in ductile-to-brittle transition region and microstructure features of low carbon microalloyed steel was established by means of multiple impact toughness tests and electron backscatter diffraction microstructure measurements. The phenomenon of local inhomogeneity in ductility of plastic zone was established on the base of different microcracks nature revealed by electron backscatter diffraction. The residual microcracks occur in local embrittled regions of material as a result of cleavage at the early stage of fracture. Pre-strained regions with local ductility variations are fractured by the formation of splittings and by the ductile tearing. Pancaked parent austenite microstructure, various ferritic microstructures and martensite-austenite constituent along with the significant grain size variations can be considered as the sources for the occurrence of remarkable impact toughness scattering in low carbon microalloyed steels during fracture in ductile-to-brittle transition region.

Synthesis of ferrimagnetic/ferroelectric composite and its magnetic and electrical characterization

The composites were synthesized using the nanoparticles of Mn0.5Zn0.5Fe2O4 and BaTiO3 via solid state route. The X-ray diffraction pattern and microstructure of the composite samples confirm the coexistence of ferroelectric and ferrimagnetic phases. The magnetization is found to increase through the inclusion of ferrite. The ferrimagnetic/ferroelectric composites show a decrease in dielectric constant value with an increase in dielectric loss by increasing ferrite-content. The variation of magnetic and dielectric properties also confirms the coexistence of ferrimagnetic and ferroelectric phase.

Investigation on synthesis of cordierite bonded porous SiC ceramics with emphasis on bond phase formation

Abstract Cordierite-bonded porous SiC ceramics were synthesized from SiC, Al2O3 and MgO powders with varying petroleum coke (PC) as the sacrificial pore former. To trace the path of development of the oxide binder phase and mechanistic steps of oxidation reaction of a PC pore former powder, thermal analysis (up to 1400 °C in air) of the precursor powders was studied with non-isothermal method varying different heating rates. The results indicated the transformation of cordierite binder phase and the average activation energy was determined to be 840 ± 27 kJ mol−1. The formation of the oxide binder phase (cristobalite (24–31 wt%) and cordierite (21–28 wt%)) and pore phase (porosity of 30–67 vol% and average pore size of 3–36 μm) were further analysed by conducting X-ray diffraction test, chemical analysis and microstructure examination for better understanding the formation of the pore phase and the binder phases of the ceramics for its applicability in the field of porous media at hostile conditions.

Minimization of the Total Depth of Internal Saw-Tooth Reliefs of a Two-Layer Relief-Phase Diffraction Microstructure

Results of studying the possibility to decrease the total depth of reliefs of a two-layer microstructure having two internal saw-tooth microreliefs reducing the dependence of the diffraction efficiency of the microstructure on the radiation wavelength and angle of radiation incidence on the microstructure are presented. These results allow one to minimize the complexity of obtaining optimum microrelief depths depending on requirements applicable to the diffraction optical element in the framework of the electromagnetic-diffraction theory. Optimum depths provide in the specified spectral range and interval of angles of radiation incidence the maximum possible (for the chosen width of the narrowest zone of the saw-tooth microrelief) value of the diffraction efficiency at the point of its minimum.

Temperature sensor based on a polymer diffraction grating with silver nanoparticles

The method is suggested for producing an optical temperature noncontact sensor on a polymer polymethylmethacrylate (PMMA) substrate with a diffraction optical element formed by implanting low-energy high-dose silver ions through a surface mask. Ion implantation is performed at an energy of 30 keV, a radiation dose of 5.0 × 1016 ion cm−2 and an ion beam current density of 2 μA cm−2 through a surface metal mask having the form of grid with square periodical holes (cells) of size 25 μm. In the course of implantation, silver nanoparticles are produced in periodical unmasked domains of irradiated PMMA. Operation of the temperature sensor on diffraction microstructures made of polymer with silver nanoparticles is demonstrated in the range from 20 °C to 95 °C by testing it with a probe radiation of a He – Ne laser.

Encapsulation and microwave hybrid processing of Al 6061–Graphene–SiC composites

ABSTRACTThe demand for new aluminum alloy–based metal matrix composites with combinations of novel reinforcements, processed through innovative methods are very much needed for critical engineering applications. With this perspective, the current research work is aimed at the development of Al 6061 composites reinforced with two-dimensional Graphene nanoflake-encapsulated SiC. Ultrasonic liquid processing method is used to disperse the Graphene flake and the mixture is ball milled by adding SiC to achieve the encapsulation. Subsequently, the Al 6061 powder is added to the milled mixture and consolidated through uniaxial vacuum hot press followed by microwave hybrid sintering. Scanning electron microscope (SEM) analysis, X-ray diffraction analysis, hardness, density, and microstructure analysis were carried out on developed composites. Raman analysis was carried out to analyze the distortion on Graphene physical structure during various processing stages. Further, effects on novel combination of material with combined processing approach on flexural and tribological behavior have been analyzed.

The effect of vanadium micro-alloying on the microstructure and the tensile behavior of TWIP steel

The effect of V addition on the microstructure and the tensile behavior of Fe-17Mn-0.45C-1.5Al-1Si-xV TWIP steel was investigated. The V additions contributed to a reduction of the grain size and an increase of the yield strength of the TWIP steels. The size distribution of various precipitates in the V-added steel, i.e. VC, TiC-VC co-precipitates and TiC, was investigated. The yield strength of the V-added steel was modelled by considering the effect of the Peierls lattice friction, solid solution strengthening, grain size refinement strengthening and precipitation hardening by the Ashby-Orowan mechanism. Electron backscattering diffraction (EBSD) microstructure analysis and constitutive modeling revealed a slight difference of the twinning behavior in the V-free and V-added steel. While a higher twinning activity was observed in the V-added steel in the early stages of deformation, more twinning was observed in the V-free steel at higher strains. It is argued that the smaller grain size in the V-added steel leads to higher localized stresses at the grain boundaries as compared to the coarser grained V-free steel, and that these higher stresses facilitate grain boundary nucleation of deformation twins in the V-added steel.