Strong Grain Research Articles

Synthesis of quantum dot-based polymer nanocomposites: assessment of their thermoelectric performances

Inhomogeneity and the presence of strong grain boundaries are responsible for the potential energy-filtering effect in the bulk state of PEDOT:PSS nanocomposites, which increases the Seebeck coefficient and electrical conductivity simultaneously.

Experimental and numerical investigations on the process quality and microstructure during induction heating assisted incremental forming of Ti-6Al-4V sheet

• Development of induction heating SPIF system to provide localized heating to deform Ti-6AI-4V alloy sheet. • A Nickel ball-roller forming tool has been integrated into the SPIF system to improve the surface quality. • The relation between mechanical and microstructural behaviours was investigated by analysing forming force, geometric accuracy, thickness profile and surface roughness with recrystallisation, grain refinement and micro-hardness throughout the process. • A Finite Element (FE) model was established to verify the experimental results. The FE obtained strain and strain rate history was used as input to form a constitutive model to investigate the microstructural evolution. • Arrhenius model has been established by calculating of Zener-Hollomon parameter (Z-parameter) to correlate the grain size and micro-hardness at specific regions. The conventional single point incremental forming (SPIF) process is unable to perform high geometrical accuracy and formability for the Ti-6AI-4V alloy sheet. In response, this article has proposed a reliable high-frequency induction heating-assisted SPIF system. Rapid localised heating (600 ℃ and 700 ℃ ) was integrated with a synchronized Inconel 625 Nickel alloy ball-roller forming tool to achieve high geometric accuracy and surface quality. This article also produced new insights into correlating mechanical and microstructural properties in SPIF at 600 ℃ and 700 ℃ . By investigating the mechanical properties (forming force, geometric accuracy, thickness profile), an explicit finite element (FE) simulation was established to predict the results. The output strain history from the FE simulations was used as input and integrated with electron backscatter diffraction (EBSD) and micro-hardness characterisations, to form a constitutive model (Arrhenius model) to calculate the Zener-Hollomon parameter (Z-parameter). The grain size and micro-hardness experimental results were correlated with Z-parameter calculation to predict the microstructural development at the initial, middle, and final stages of the deformation process. The mechanical results revealed that the 700 ℃ experiment performed enhanced geometric accuracy and thickness profile, with a reduced forming force. However, the surface quality is reduced as the lubricant dissipated rapidly, while the ball-roller tool effectively compensated for this behaviour by reducing the friction. At the microstructural level, 600 ℃ revealed strong strain hardening and grain deformation, and 700 ℃ revealed better grain refinement by dynamic recovery (DRV) and dynamic recrystallisation (DRX). A proportional relationship between Z parameters and grain size and a low-high-low micro-hardness profile was proposed.

Flaw Detection in Highly Scattering Materials Using a Simple Ultrasonic Sensor Employing Adaptive Template Matching.

Ultrasonic sensors have been extensively used in the nondestructive testing of materials for flaw detection. For polycrystalline materials, however, due to the scattering nature of the material, which results in strong grain noise and attenuation of the ultrasonic signal, accurate detection of flaws is particularly difficult. In this paper, a novel flaw-detection method using a simple ultrasonic sensor is proposed by exploiting time-frequency features of an ultrasonic signal. Since grain scattering mostly happens in the Rayleigh scattering region, it is possible to separate grain-scattered noise from flaw echoes in the frequency domain employing their spectral difference. We start with the spectral modeling of grain noise and flaw echo, and how the two spectra evolve with time is established. Then, a time-adaptive spectrum model for flaw echo is proposed, which serves as a template for the flaw-detection procedure. Next, a specially designed similarity measure is proposed, based on which the similarity between the template spectrum and the spectrum of the signal at each time point is evaluated sequentially, producing a series of matching coefficients termed moving window spectrum similarity (MWSS). The time-delay information of flaws is directly indicated by the peaks of MWSSs. Finally, the performance of the proposed method is validated by both simulated and experimental signals, showing satisfactory accuracy and efficiency.

Control of Thousand-Grain Weight by OsMADS56 in Rice.

Grain weight and size are important traits determining grain yield and influencing grain quality in rice. In a previous study, a quantitative trait locus controlling thousand-grain weight (TGW) in rice, qTGW10-20.8, was mapped in a 70.7 kb region on chromosome 10. Validation of the candidate gene for qTGW10-20.8, OsMADS56 encoding a MADS-box transcription factor, was performed in this study. In a near-isogenic line (NIL) population segregated only at the OsMADS56 locus, NILs carrying the OsMADS56 allele of IRBB52 were 1.9% and 2.9% lower in TGW than NILs carrying the OsMADS56 allele of Teqing in 2018 and 2020, respectively. Using OsMADS56 knock-out mutants and overexpression transgenic plants, OsMADS56 was validated as the causal gene for qTGW10-20.8. Compared with the recipients, the TGW of the knock-out mutants was reduced by 6.0–15.0%. In these populations, decreased grain weight and size were associated with a reduction in the expression of OsMADS56. In transgenic populations of OsMADS56 driven by a strong constitutive promoter, grain weight and size of the positive plants were significantly higher than those of the negative plants. Haplotype analysis showed that the Teqing-type allele of OsMADS56 is the major type presented in cultivated rice and used in variety improvement. Cloning of OsMADS56 provides a new gene resource to improve grain weight and size through molecular design breeding.

Effects of complex strain conditions on macroscopic deformation behavior in basal plane of Mg alloy

Severe plastic deformation increases the defect density and forms an ultrafine grain structure by applying a complex stress state that includes plane and shear deformations to a high strain. However, it is not yet clear how the complex stress state with the added shear strain changes the deformation mechanism. To understand the effect of macroscopically applied shear strain on simple plane strain, tensile test specimens with a special notch (complex stress state) were compared to a general tensile test specimen (simple plane strain) using a Mg alloy. To unify the slip system activation, the normal directions of the tensile test and the notch tensile test were set parallel to the normal direction of the {0001} planes of the strongly textured Mg alloy. The addition of shear strain unexpectedly weakened the average dislocation density and the screening behavior of dislocations, while strain accommodation by deformation twinning accelerated. Additionally, as the equivalent strain increased to 0.2, the general tensile test exhibited de-twinning behavior, whereas the twin fraction continuously increased when a complex strain was applied. The reason for the different deformation mechanisms is considered to be the strong grain rotation behavior under complex strain conditions, which fortifies the stress concentration at grain boundaries. This implies that complex strain with shear strain can accelerate deformation twinning while suppressing dislocation slip when basal slip is dominant.

Effect of Iron Content on Corrosion Properties of Pure Titanium as Grain Refiner.

Microstructures and corrosion properties of pure titanium were characterized when iron was used as a grain refiner. The added Fe element acted as a strong grain refiner for pure titanium by forming β Ti phase at grain boundaries, and 0.15 wt% Fe was revealed to be a sufficient amount to make the grain size of pure titanium below 20 μm, which was the requirement for the desired titanium cathode. However, corrosion resistance was decreased with the Fe amount added. From the open circuit potential (OCP) results, it was obvious that the TiO2 stability against the reducing acid environment was deteriorated with the Fe amount, which seemed to be the main reason for the decreased corrosion resistance. Electrochemical impedance spectroscopy (EIS) results showed that both the decrease in the compact oxide film’s resistance (Rb) and the appearance of the outer porous film occurred as a result of the dissolution of the TiO2 layer, whose phenomena became more apparent as more Fe was added.

Achieving high damping capacity and strength simultaneously in a high-zinc aluminum alloy via melt spinning and hot extrusion

High-Zn AlZn alloys exhibited a high damping capacity but a low strength, which restricted their applications in many structural components under vibration conditions. To overcome this problem, grain refinement and alloying (by adding Mg, Cu and Zr) were employed to enhance the strength of high-Zn AlZn alloys while retaining the high damping capacity. In this work, fine-grained high-Zn AlZnMgCuZr alloys extruded at different extrusion ratios were achieved by a combination of melt spinning and hot extrusion. The rapidly-solidified and extruded alloys were observed to contain numerous second-phase particles (Zn and η-phase) at grain boundaries, high-density nano-sized precipitates (GP-zones and η′-phase) present in equiaxed α-Al grains, along with high solute solubility and many ribbon interfaces. These special microstructural features provided the high-Zn alloys with excellent room/high-temperature damping capacity and high strength. With increasing extrusion ratio, the damping capacity decreased gradually due to the reduction in the density of second-phase particles, the increases in both solute solubility of α-Al matrix and density of coherent GP-zones, and the improvement of bonding strength of ribbon interfaces. The overall high strength of the high-Zn alloys was attributed to strong grain refinement strengthening, solution strengthening and precipitation strengthening.

Microstructural Master Alloys Features of Aluminum–Erbium System

Aluminum master alloys with rare earth metals are widely studied by many scientists around the world, but research on the production of Al-Er master alloys is still limited. The purpose of this work is to study the microstructure parameters of aluminum-erbium master alloys obtained by metallothermic reduction of salt mixtures containing erbium oxide or fluoride. The structural features were investigated by optical and scanning electron microscopy, and the dependence of the microhardness of the eutectic and solid solution fields of obtained master alloys on the content of erbium in the master alloy was determined. Studies have shown that master alloys obtained by metallothermic reduction of erbium compounds from chloride–fluoride melts are characterized by a uniform distribution of Al3Er intermetallic compounds in the volume of double eutectic [(Al) + Al3Er] and have a strong grain refinement effect. The analysis of the microstructure showed that the structure of the master alloys varies depending on the content of erbium. When the content of erbium in the master alloy is up to 6 wt.%, the eutectic structure is preserved. When the content of erbium in the master alloy is 8 wt.% or more, the structure becomes a solid solution with individual inclusions of various shapes and intermetallic compounds.

Recent progress of thick tungsten coating prepared by chemical vapor deposition as the plasma-facing material

Chemical vapor deposition (CVD) is a promising technique for the preparation of W-based plasma-facing materials (PFMs). An overview of the microstructure, chemical composition, thermal conductivity, thermal stability, thermal shock performance under disruption-like and edge localized mode-like transient heat load, and neutron irradiation performance of CVD-W has been given in our previous work. However, for fusion applications, additional properties need to be assessed. To this end, deuterium (D) permeability, D plasma irradiation performance, and thermal fatigue resistance of CVD-W were investigated in this work. The results showed that the D permeability of CVD-W in the temperature range of 973–1173 K was larger than that of the commercial pure W, which was related to the columnar grain structure of CVD-W. Additionally, both CVD-W and commercial pure W were exposed to D plasma up to a fluence of 1 × 1026 m−2. Compared to commercial pure W, CVD-W exhibited a mitigated blistering behavior and lower D total retention, which could be attributed to its strong [001] crystallographic texture along the thickness direction and a lower number of defect density (e.g. grain boundaries). CVD-W and commercial pure W were also exposed to steady-state and transient heat load simultaneously, leading to a base surface temperature and surface temperature increase of about 953–1473 K and 250–300 K, respectively. A strong grain orientation dependence of the surface degradation induced by the combined heat load has been found. Consequently, CVD-W exhibited a much more uniform plastic deformation than pure W, and no surface cracks along grain boundaries were observed in CVD-W. Finally, the industrial-scale production of CVD-W-based PFMs and mockups was demonstrated. This work paves the way for the fusion applications of thick CVD-W coatings.

Evolution of microstructure and texture in pipeline steels at different TMCP procedures with regard to hydrogen induced cracking

SEM and EBSD techniques are used to evaluate hydrogen induced cracking susceptibility in API X70 pipeline steels produced by thermo-mechanical controlled process (TMCP) in laboratory scale. Based on the observations, there is no dominant texture in the specimens and the grains are randomly distributed. Different TMCP parameters and rolling processes generates different grain size, and grains are often elongated along the rolling direction. The results also show that cooling rate is another factor affecting the grain size. A high cooling rate does not allow the grains to grow. The reason for the transgranular type of cracking might be the strong grain boundaries in ambient temperatures which prevents the intergranular cracking. Based on experiments, the hydrogen environment does not have permanent effects on the mechanical properties of the investigated specimens. The electrochemical hydrogen charging experiment shows that the grain refinement improves the resistance to hydrogen embrittlement.

Genetic Manipulation of M13 Bacteriophage for Enhancing the Efficiency of Virus‐Inoculated Perovskite Solar Cells with a Certified Efficiency of 22.3% (Adv. Energy Mater. 38/2021)

Virus-Inoculated Perovskites In article number 2101221, Jin-Woo Oh, Hyung Do Kim, Il Jeon, and co-workers report genetic modification of M13 bacteriophages to amplify amino acid K, which functions as a perovskite growth template and a stronger passivator than the wild-type virus in PSCs. The modified virus-added perovskite solar cells exhibited a higher efficiency of 23.6% than the wild-type counterparts (22.8%). The observed enhancement is attributed to slightly larger perovskite grains and strong grain boundary passivation. The obtained device efficiency has been certified by the national research center.

Nonlinear stiffness and damping characteristics of gravelly crushed rock: Developing generic curves and attempting multi-scale insights

Gravelly soils and aggregates composed of crushed rock are commonly encountered in a variety of applications in geotechnical, transportation and infrastructure engineering projects, while gravel-sized materials, often in the form of soil mixtures, are also found in natural deposits in alluvial, glacial and shoreline environments. Despite the significant amount of research being conducted on the dynamic properties of soils, less attention has been given on the assessment and modeling of the behavior of gravel-sized materials, particularly in the range of medium strains, where stiffness and damping have a nonlinear relationship with strain amplitude. In the present study, laboratory data stemming from resonant column tests published in the literature are re-analyzed with emphasis on gravel-sized crushed rock of strong and hard grains and the range of small-to-medium strain amplitudes. The test samples had a mean grain size in the range of 1.5–10 mm and a coefficient of uniformity from 1 to 13. The stiffness reduction curves are studied by means of the Oztroprak-Bolton hyperbolic model and from the data analysis, correlations are developed for the reference strain, the linear threshold strain and the curvature coefficient, which are then incorporated as model parameters into the hyperbolic expression. For the damping increase curves, a correlation is proposed with respect to the stiffness values, taking into account normalizations for small-strain material damping. The analysis led to the development of generic stiffness reduction and damping increase curves which are compared with previous data and models published in the literature for a variety of soils. These comparisons show that for crushed rock of irregular-in-shape grains (i.e., elongated and angular grains), significant differences are observed on the stiffness reduction and damping increase curves between gravels and sands with the gravels displaying higher non-linearity with shifted reference strain and linear threshold strain to smaller values. This was particularly highlighted for uniform gravels compared with uniform sands, whereas a convergent of the generic curves between sands and gravels was observed for high values of the coefficient of uniformity. Thus, existing relationships developed on the basis of granular materials of rounded particles and specifically expressions on the basis of sand-sized materials should be cautiously used in the deformation analysis of problems involving gravelly crushed rock and natural soils of irregular-in-shape grains, particularly for uniform to poorly graded materials.

The Phase Transformations Induced by High-Pressure Torsion in Ti–Nb-Based Alloys

The study of the fundamentals of the α → ω and β → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Prior to HPT, three alloys with 5, 10, and 20 wt% of Nb were annealed in the temperature range of 700–540°C in order to obtain the (α + β)-phase state with a different amount of the β-phase. The samples were annealed for a long time in order to reach equilibrium Nb content in the α-solid solution. Scanning electron microscope (SEM), transmission electron microscopy, and X-ray diffraction techniques were used for the characterization of the microstructure evolution and phase transformations. HPT results in a strong grain refinement of the microstructure, a partial transformation of the α-phase into the ω-phase, and a complete β → ω phase transformation. Two kinds of the ω-phase with different chemical compositions were observed after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the almost Nb-pure α-phase. It was found that the α → ω phase transformation depends on the Nb content in the initial α-Ti phase. The less the amount of Nb in the α-phase, the more the amount of the α-phase is transformed into the ω-phase.

Novel estimation method for anisotropic grain boundary properties based on Bayesian data assimilation and phase-field simulation

Utilizing the data assimilation and multi-phase-field grain growth model, this study proposes a novel framework of measuring anisotropic (nonuniform) grain boundary energy and mobility. The framework can evaluate a large number of boundary properties from typical observations of grain growth without requiring specifically designed experiments or calculations. In this method, by optimizing the multi-phase-field model parameters such that the simulation results are in good agreement with the observation data, the energies and mobilities of multiple individual boundaries are directly and simultaneously estimated. To validate the method, numerical tests on boundary property estimation were performed using synthetic microstructure dataset generated from grain growth simulations with a priori assumed property values. Systematic tests on simple tricrystal systems confirmed that the proposed method accurately estimates each boundary energy and mobility within an error of only several % of their assumed true values even for conditions with strong property anisotropy and grain rotation. Further numerical tests were conducted on a more general multi-grain system, showing that our method can be successfully applied to complicated polycrystalline grain growth. The obtained results demonstrate the potential of the proposed method in extracting a large dataset of grain boundary properties for arbitrary boundaries from actual grain growth observations.

Investigation on the Strengthening Mechanism of Flow Control Extrusion by Using Experiment and Numerical Simulation.

Bimodal grain structure leads to high strength and strain hardening effect of metallic materials. In this study, an effective approach called flow control extrusion (FCE) is proposed to achieve heterostructures of pure copper. Compared with conventional extrusion (CE), FCE shows much stronger grain refine ability and much weaker grain orientation concentration. The significant grain refinement and heterostructures depend on the severe shear strain from FCE. The heterostructures of sample subject to FCE transfer from bimodal structure to gradient structure with the decrease of temperature, as the grains in the surface of sample are all refined to ultrafine scale. Both these two heterostructures can realize the improvement of strength and strain hardening effect simultaneously.

Evaluation of dislocation activities and accumulation in cold swaged CoCrFeMnNi high entropy alloy

The CoCrFeMnNi high entropy alloys (HEAs) performs large work strengthening with excellent deformability. The work strengthening and deformation mechanism are facilitated by dislocation activities and dislocation accumulation. In this study, the dislocation density and microstructure of the CoCrFeMnNi HEA were characterized by the neutron line profile analysis using convolution multiple whole profile (CMWP) method and EBSD in a comparison with a binary FeNi alloy. The CoCrFeMnNi HEA and FeNi alloy were plastically deformed by rotary swaging until 85% area reduction. The characteristics (e.g., low stacking fault energy, local variation with different atom species) rising from the high compositional complexity of the CoCrFeMnNi HEA cause different dislocation activities and levels of dislocation accumulation from the binary FeNi alloy. The dislocation density of the CoCrFeMnNi HEA continuously increased during the cold swaging and was significantly larger than the FeNi alloy. The larger dislocation accumulation of the CoCrFeMnNi HEA is facilitated by higher compositional complexity, extensive dislocation arrangement, and strong grain fragmentation. The increasing heterogeneity of dislocation distribution in the CoCrFeMnNi HEA was contributed by dislocation cell formation and increasing geometrically necessary dislocations (GNDs). The larger work strengthening in CoCrFeMnNi HEA is correlated with large total dislocation density during cold swaging.

Phase Transformations in the AlMg Alloys Driven by High‐Pressure Torsion

As‐cast aluminum–magnesium alloys with 3, 5, and 10 wt% Mg are subjected to high‐pressure torsion (HPT) at room temperature: 5 GPa, five turns with rotation speed of 1 rpm. HPT leads to the strong grain refinement for both (Al) solid solution and intermetallic β‐phase. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD) are used to characterize the phase transitions under heating of the HPT‐treated alloys. The decomposition of the solid solution in the ultrafine‐grained Al–10 wt% Mg alloy obtained by HPT does not follow the equilibrium diagram. The results of DSC, XRD, and TEM show that the Mg‐rich intermetallic phases appear during heating in the following sequence: GP zones → β → ε → β → γ → β. The (Al)/(Al) grain boundaries (GBs) in the fine‐grained Al–10 wt% Mg alloy after HPT and annealing up to 400 °C (i.e., in the solid solution area, far from solvus and solidus lines) contain the Mg‐rich areas. This can be the result of possible GB phase transitions with the formation of Mg‐rich GB phases. The GBs in the binary AlMg can contain the thin layers of a GB phase far away from the solvus line.

Controls on the grain size distribution of landslides in Taiwan: the influence of drop height, scar depth and bedrock strength

Abstract. The size of grains delivered to rivers by hillslope processes is thought to be a key factor controlling sediment transport, long-term erosion and the information recorded in sedimentary archives. Recently, models have been developed to estimate the grain size distribution produced in soil, but these models may not apply to active orogens where high erosion rates on hillslopes are driven by landsliding. To date, relatively few studies have focused on landslide grain size distributions. Here, we present grain size distributions (GSDs) obtained by grid-by-number sampling on 17 recent landslide deposits in Taiwan, and we compare these GSDs to the geometrical and physical properties of the landslides, such as their width, area, rock type, drop height and estimated scar depth. All slides occurred in slightly metamorphosed sedimentary units, except two, which occurred in younger unmetamorphosed shales, with a rock strength that is expected to be 3–10 times weaker than their metamorphosed counterparts. For 11 landslides, we did not observe substantial spatial variations in the GSD over the deposit. However, four landslides displayed a strong grain size segregation on their deposit, with the overall GSD of the downslope toe sectors being 3–10 times coarser than apex sectors. In three cases, we could also measure the GSD inside incised sectors of the landslides deposits, which presented percentiles that were 3–10 times finer than the surface of the deposit. Both observations could be due to either kinetic sieving or deposit reworking after the landslide failure, but we cannot explain why only some deposits had strong segregation. Averaging this spatial variability, we found the median grain size of the deposits to be strongly negatively correlated with drop height, scar width and depth. However, previous work suggests that regolith particles and bedrock blocks should coarsen with increasing depth, which is the inverse of our observations. Accounting for a model of regolith coarsening with depth, we found that the ratio of the estimated original bedrock block size to the deposit median grain size (D50) of the deposit was proportional to the potential energy of the landslide normalized to its bedrock strength. Thus, the studied landslides agree well with a published, simple fragmentation model, even if that model was calibrated on rock avalanches with larger volume and stronger bedrock than those featured in our dataset. Therefore, this scaling may serve for future modeling of grain size transfer from hillslopes to rivers, with the aim to better understanding landslide sediment evacuation and coupling to river erosional dynamics.

Mechanism of large strain accommodation assisted by shear localization in a precipitation-hardened Cu–Be alloy

The influence of the structural state on deformation mechanisms under large strains was investigated in a Cu – 2 wt.% Be alloy. Torque evolutions during straining exhibit serrations typical of structural relaxations in the precipitation-hardened alloy, but not in the solid solution state. Microstructure characterization revealed that homogeneous deformation of the solid solution led to strong grain size reduction (20 nm), while localization occurred in the precipitated state with numerous shear bands. The role of CuBe precipitates on hindering dislocation glide and the resulting shear localization under large strain is discussed.

Softening mechanisms in ultrasonic treatment of deformed austenitic stainless steel

The effect of ultrasonic treatment on the microstructural evolution and the related softening process in tensile pre-deformed 316 stainless steel was studied by means of electron backscatter diffraction method, optical microscopy, and microhardness measurement. It was observed that different levels of ultrasonic energy induced complex microstructural changes in the treated samples. A large decrease in twin boundaries was observed, which is an indication of the de-twinning process under ultrasonic treatment. A new mechanism for the de-twinning process under oscillatory stress of ultrasonic vibration was proposed. It was shown that de-twinning under ultrasonic treatment led to dislocation production from twin boundaries. Inverse pole figures investigation revealed strong grain rotation following ultrasonic treatment in tensile pre-deformed samples. Subgrain formation in the ultrasonic treated austenitic stainless steel samples indicated that considerable ultrasonic energy was induced by the ultrasonic vibration, which provided the activation energy needed for dislocation climb and cross-slip. The ultrasonic induced subgrain formation, dislocation annihilation, and de-twinning, which resulted in a decrease of the microhardness in the samples, can be considered as possible mechanisms for the acoustic softening in the austenitic stainless steels.