Microstructural Scale Research Articles

Grain-boundary segregation and grain growth in nanocrystalline substitutional solid solution alloys

A model for describing solute segregation at grain boundaries has been developed for substitutional solid solution alloys, which integrates multiple factors from atomic to microstructural scales. A concept of molar Gibbs free energy of segregation was introduced to evaluate the segregating capability of the solute elements in a closed system, through which the influences of grain boundary structure, grain size, material composition, and external conditions were described. Based on the evaluation of various energy forms related to solute segregation and grain growth processes, the nature of the thermal stabilization of nanograin structures by solute segregation was disclosed. A criterion for the destabilization of nanostructures, which is determined by the competition of the change rates between the molar Gibbs free energy of segregation and the total energy of grain boundaries with grain size, has been proposed. This study provided guideline to achieve high-temperature stability of nanograin structures of solid solution alloys even for the weakly segregating nanocrystalline systems.

A two-stage study of steel corrosion and internal cracking revealed by multimodal tomography

Modeling of corrosion-induced cracking is limited by lacking knowledge on the behavior of corrosion products. In this work, the corrosion and cracking processes were experimentally investigated in 3D at two different stages. The processes were measured at micro-structural scale, applying nondestructive neutron and X-ray computed tomography in two scans at different stages in the corrosion process. A method to evaluate the average volumetric strain of the compressed corrosion layer was proposed and displacements in the concrete matrix were measured. Strain localization revealed cracks not directly visible in the images. Multimodal tomography demonstrated to be an effective method for investigating steel corrosion in reinforced concrete.

Microstructure response to shear strength deterioration in loess after freeze-thaw cycles

Shear strength deterioration owning to freeze-thaw (F-T) cycles affects loess slope stability in seasonal frozen region. The change in loess shear strength is closely related to particle microstructure. In this study, multiple F-t-tests (i.e., 0, 1, 3, 5, 10, 15, 20, and 30 cycles) were performed on natural loess from Jing'yang, China. Unconsolidated-undrained triaxial tests and scanning electron microscopy (SEM) were performed on the specimens after the predefined number of F-T cycles. Particle microstructure was quantitatively analyzed using fractal dimension theory. The relationship between shear strength index and particle microstructure characteristics parameters was evaluated using the grey correlation method. Changes in the loess microstructure involved two main processes: transformation and stabilization, and the particle shape, arrangement, and interparticle contact were transformed into different types. The particle shape changed from complex to round with debris detaching from the particle surface. The orderliness of particle arrangement increased and point-face intercontact was formed. The internal friction angle and cohesion decreased with an increasing number of F-T cycles, and the change pattern was similar to that of the particle microstructure characteristics, both of which changed significantly before 5 F-T cycles and stabilized after 15 F-T cycles. An evaluation of the correlation between shear strength index and particle microstructure characteristic parameters demonstrated that, the change in particle shape contributed the most to deterioration of shear strength during F-T cycles, followed by particle arrangement and particle distribution. These results provide insights into the mechanism of degradation of loess shear strength in seasonally frozen areas at the microstructural scale.

Soft magnetic composite based on iron in sintered Mn–Zn ferrite matrix without non-magnetic coating

Low core loss soft magnetic composites based on iron powder particles encapsulated in CoO- and TiO2-doped sintered Mn–Zn spinel ferrite matrix are fabricated with no additional organic nor inorganic non-magnetic insulating layer. As both the iron and ferrite contribute to the entire effective composite properties with their ferromagnetic and ferrimagnetic nature, respectively, the resulting composites possess improved magnetic performance. The absence of any non-magnetic binder ensures higher ability of iron-matrix magnetic coupling. The temperature-dependent properties are tuned to higher level of operating temperatures of about 200 °C. The magnetic losses are shown to be suppressed thanks to the high electrical resistivity of ferrite insulation and permeability is enhanced because of the collectivization of iron particles and ferrite grains in magnetization process. This unique property descends from mediating the paths for magnetic flux between iron particles by ferrite matrix which, at the same time, mitigates the demagnetizing effects on the scale of composite's microstructure.

LaFeO3 thin films on Yttria Stabilized Zirconia flexible substrate

Thin films of LaFeO3 for photocatalytic applications were grown by Pulsed Laser Deposition on a flexible polycrystalline Tetragonal Yttria Stabilized Zirconia substrate (T-YSZ). Their structure and morphology were investigated using scanning electron microscopy, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy (STEM), energy dispersive spectroscopy available in the STEM system, X-ray diffraction, and Raman spectroscopy techniques. The band gap energies and the life time of the charge carrier were deduced from UV-Vis and time resolved fluorescence spectroscopies. The polycrystalline substrate T-YSZ was homogeneously covered by the LaFeO3 films, even at the substrate grain boundaries. The surface of the films presents a nanostructuration with flat ended and tip ended grains. The exposed facets are mainly {100}C. Atomic–scale microstructure investigations revealed twins in LaFeO3 grains, as consequence of the curvature of the T-YSZ substrate. Chemical analyses showed iron and oxygen deficiency in the LaFeO3 layers. Two optical transitions with energies of 1.9 eV and 2.5 eV corresponding to visible light absorption were evidenced, and the average life time of charges carriers was found to be 5 ns.

Fe-modified Mn2CuO4 spinel oxides: coatings based on abundant elements for solid oxide cell interconnects

The current state of the art steel interconnect coating materials are based on critical raw material - Co-oxide spinels. Replacing Co-oxide spinels with alternative, abundant materials can reduce the dependence on the critical raw materials. Cobalt-free coatings with the general formula Mn2-xCuFexO4, where x = 0, 0.1, 0.3, were electrophoretically deposited on a ferritic stainless-steel support and evaluated. Prior to deposition, the powders were prepared by a soft chemistry process and studied in terms of crystallographic phase analysis, electrical conductivity, thermal expansion, and sinterability behaviour. Coated steel samples were oxidised in an air atmosphere at 750 °C for 3000 h. In parallel, a state-of-the-art MnCo2O4 spinel oxide was tested as a reference. The coatings and oxide scale microstructures of the surfaces and cross-sections were examined by XRD, and SEM-EDX. TEM-EDX, XRF, and micro-XRD were also performed on the cross-section lamellae. The electrical properties of the steel-coating system were evaluated by Area Specific Resistance measurement. The results confirm that Mn–Cu–Fe oxides exhibit higher conductivity and lower TEC than Mn–Co oxide. Based on the obtained results, it might be concluded that the proposed coatings are a promising alternative to coatings that contain cobalt.

Chopped Basalt Fiber-Reinforced High-Performance Concrete: An Experimental and Analytical Study

Basalt fiber (BF) is an environmentally friendly type of fiber that has attracted the attention of researchers in recent years due to its excellent performance in concrete constructions. This current research was conducted to investigate the effect of chopped basalt fiber on the workability, compressive strength, and impact resistance of high-performance concrete (HPC). Three various lengths (3, 12, and 18 mm) and six volume fractions (0%, 0.075%, 0.15%, 0.3%, 0.45%, and 0.6% by concrete volume) of BF were used in producing sixteen HPC mixes. HPC compressive strength and impact resistance were measured for each mix. Scanning electron microscopy (SEM) analysis was also conducted on selected mixes to closely investigate the effects of the applied variables through the microstructural scale. An empirical model was developed to study the relationship between the impact energy and compressive strength of BF-reinforced HPC. The results show that adding BF improves the compressive strength and impact resistance. Compared with the control concrete, the compressive strength of the HPC reinforced with 3 mm, 12 mm, and 18 mm BF increased by 12.2%, 15.1%, and 17.5%, respectively. The impact resistance increased with a dosage of 8 kg/m3 for all lengths of BF. The SEM observations revealed that the BF accumulated in pores and on the surface of the attached cement which improved the microstructure of the interfacial transition zone (ITZ), which further enhanced the strength and ductility of the HPC.

Effect of gas composition on the oxide scale growth mechanisms in a ferritic steel for solid oxide cell interconnects

The oxidation behavior of a ferritic steel Fe-23Cr-0.5Mn-0.6 Nb-0.1Ti (at%) considered for application in solid oxide cell (SOC) stack interconnects was studied at 800 °C. The oxidation kinetics and oxide scale microstructure formed in Ar-20%O2, Ar-4%H2-4%H2O and Ar-1%CO-1%CO2 atmospheres, simulating the SOC operation environments, were investigated by thermogravimetry (TG) in conjunction with electron microscopy (SEM/TEM) and atom probe tomography (APT). In all three environments multilayered oxide scales formed, consisting of Mn-Cr spinel on top of Cr2O3 and an additional Nb-rich oxide layer at the chromia-alloy interface. The initially faster oxidation in the low pO2 gases was attributed to formation of porous chromia scales compared to a dense scale formed in the high pO2 (Ar-O2) atmosphere. APT revealed segregation of minor alloying elements (Mn, Nb and Ti) to chromia grain boundaries in all three simulated SOC environments in quantitatively similar amounts, suggesting their similar effect on the ionic transport through the oxide scale. The findings indicate that oxygen activity in the test gas plays a dominating role in governing the oxidation kinetics and the oxide scale microstructure of the studied ferritic steel.

Light and scanning electron microscopic characterization of the Egyptian buffalo hair in relation to age with analysis by SEM-EDX.

The purpose of this study was to demonstrate a relationship between the microstructure and measurements of Egyptian buffalo hair and age. The buffalo studied ranged in age from young to premature to adult (3-8 months, 1.5-3, 4-6, and 8-10 years). The hair was collected from the animals' withers. Cuticle elements were examined using scanning electron microscopy (SEM), light microscopy, and energy-dispersive X-ray (EDX) analysis. Hair shaft diameter increased with age, according to SEM and light microscopy measurements. The values of shaft diameter obtained by SEM of the same animal were 64%-67% of the values obtained by light microscopy due to shrinkage of the hair during the drying process. Additional microscopy measurements revealed that the width of the cortex and medulla increased with age, while the width of the cuticle decreased slightly. The medulla index of four different age groups ranged from 0.56 to 0.61 μm. The average distance between successive scale values increased from 4.83 μm in the young group to 8.86 μm between the ages of 8 and 10 years. The scale pattern had a distinct personality at each stage of age. The hair medulla was in the center and consisted of a mesh-like structure with large pores divided into smaller pores by septa. The cortex was a bundle of fibers that wrapped around the medulla. Light microscopy revealed small oval granules and large streak-like granules in the cortex. EDX spectra revealed that carbon, oxygen, and nitrogen were shown to be more abundant in all age groups of buffalo. In buffalo hair, oxygen was the second most abundant element after carbon. The carbon mass in the examined samples decreased slightly with age (42.31%, 39.18%, 38.88%, and 38.49%), while oxygen increased with age. We concluded that hair measurements varied with age, scale microstructure, and elements, so we estimated buffalo animals' ages up to 10 years. HIGHLIGHTS: The goal was to show a link between the microstructure and measurements of Egyptian buffalo hair and age. Hair shaft diameter increased with age, according to scanning electron microscopy (SEM) and light microscopy measurements. The hair shaft diameter obtained by light microscopy was higher than that obtained by scanning electron microscopy of the same animal; we hypothesized that the difference in hair shaft diameter measured by light microscopy and scanning electron microscopy of the same animal was due to the shrinkage of the hair during the drying process. The width of the cortex and medulla increased with age, while the width of the cuticle decreased slightly. The average distance between successive scale values increased from 4.83 μm in the young group to 8.86 μm between 8 and 10 years old. At each stage of age, the scale pattern had a distinct personality. Carbon, oxygen, and nitrogen were found to be more abundant in the hair of buffalo of all ages and were detected using energy-dispersive X-ray (EDX) spectra. After carbon, oxygen was the second most abundant element in buffalo hair. The carbon mass in the samples studied decreased slightly with age, while the oxygen mass increased. Hair measurements varied according to age, scale microstructure, and elements.

Effect of TiAlNbCrSi Alloy Microstructure Produced by Mould Casting (MC) or Electron Beam Powder Bed Fusion (EB-PBF) on Scale Grown Under Dry Air and Steam

TiAl parts fabricated with additive manufacturing have begun to find applications in car and aviation industry. Optimization of their properties concentrates on introduction of new alloying additions improving the TiAl ductility and oxidation resistance. Their effect on the mechanical properties was worked out quite well, but the knowledge how they affect the oxidation processes is still limited. Therefore the present experiment was aimed at investigation of scale grown over mould cast (MC) and electron beam powder bed fusion (EB-PBF) Ti–48Al–2Nb–0.7Cr–0.3Si (at. pct) alloys. It was conducted at 650 °C for 1000 hours both in dry air and steam covering early stages of this process. The scale microstructure, chemical and phase composition was examined with the transmission electron microscopy (TEM). Applied treatment caused development of three-layer scale, i.e. with major portions of R-TiO2 + α-Al2O3/R-TiO2/α-Al2O3. The one formed during dry-air oxidation of the EB-PBF alloy was most compact. Steam oxidizing changed morphology of rutile present at its surface from rod/plate-like into whiskers. The Si turned out to be especially active during scale growth diffusing up to its surface. The presence of steam further increased mobility of both Si and Cr rising their presence in the upper part of the scale. The Nb was found to accumulate within the substrate area adjoining to the scale. Refinement of EB-PBF microstructure as compared with the MC alloy resulted in promoting reaction at the scale/substrate front contributing significantly to development of thicker oxide coating and nitrides bearing oxidation affected zone.

Influence of the Anodizing Time on the Microstructure and Immersion Stability of Tartaric-Sulfuric Acid Anodized Aluminum Alloys

Tartaric-sulfuric acid anodizing (TSA) has been selected by the aerospace industry to replace Cr(VI)-based anodizing treatments of aluminum alloys. Modification of the bath composition can result in the necessity to revise the process conditions, including the time necessary to obtain the desired properties of the anodized layer. This study focuses on the microstructure and immersion stability of the pilot scale anodized AA2024 aluminum alloy, with anodizing times of 25 min and 45 min. The layer structure was characterized by scanning electron microscopy (SEM) and glow discharge optical emission spectrometry (GD-OES). The electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion resistance and immersion stability of the samples in 0.01 M NaCl solution. The density of pores formed in the 45 min anodized samples was higher which correlated with higher impedance modulus at equivalent immersion time and higher thickness of the oxide layer. Contact angle measurements demonstrated better wettability of the 45 min anodized sample. The results suggest that 45 min anodizing offers higher corrosion resistance and better initial adhesion with subsequent post-treatment such as sealing or painting.

Mechanistic modelling of fatigue nucleation and short crack growth in polycrystalline alloys

This paper proposes an engineering approach at the microstructural scale to the problem of fatigue crack initiation. Initiation of an engineering fatigue crack approximately 0.2–0.4 mm in size is broken down into the separate processes of nucleation of a small facet, and subsequent short crack growth of the facet to an engineering crack. Engineering fatigue models frequently don't consider these processes separately and have difficulty predicting the total initiation life as the distributions of the separate processes are not known. A fundamental approach to modelling initiation life that tries to address these issues has been developed. A combination of crystal plasticity and the extended finite element method are used to model nucleation followed by short crack growth. The crack growth rate is calculated using the local stored energy at the crack tip, crack growth occurs on the crystallographic plane with the largest accumulated slip, thus allowing crack tortuosity to be modelled. A grain boundary hardening model has been developed which reduces the local stored energy available for growth at grain boundaries resulting in growth retardation. The levels of retardation experienced are in agreement with published data for a range of materials. The method has been successfully correlated with fatigue data for coarse grain RR1000.

A comprehensive study on size-effect, plastic anisotropy and microformability of aluminum with varied alloy chemistry, crystallographic texture, and microstructure

Fabrication of microparts with large aspect-ratio and complex shapes remains a huge challenge for industries and microforming is a potential solution to manufacture such microparts. However, similarity in specimen-deformation and microstructural length scales during microforming results in size effect, leading to unpredictable plastic behavior and increased process scatter. One approach to counter size effect is by engineering suitable microstructure in the material. In the present work, three grades of Al (AA1070, AA5083, AA2014) with unique alloy chemistry and microstructural profile are processed by cryorolling (CR) to 95% thickness reduction. By imparting controlled postprocess annealing on the CR materials, three distinctive microstructures – (i) ultrafine grained (UFG) with average grain size around 1 μm, (ii) fine grained (FG) with average grain size near to 5 μm, and (iii) coarse grained (CG) with approximate average grain size of 20 μm are engineered. The influence of alloy chemistry, grain boundary engineering and crystallographic texture on microformability are studied. For pure Al (AA1070), the UFG and FG microstructures show superior microformability than the CG counterparts. The equiaxed UFG grains present in these microstructures mitigate the size effect abnormalities by increasing the number of grains in the deformation volume and uniformly distributing the complex microforming strain via grain boundary mediated plasticity. Their corresponding texture containing strong Copper mixed with scattered Cube elements promotes in-plane strain condition and high resistance to localized thinning. Also, the material shows near-zero planar anisotropy that leads to a homogenous in-plane strain distribution. Unlike pure Al, the UFG and FG Al alloys suffer from increased strain localization due to presence of solute clouds and nanoprecipitates. They influence strain-aging (Portevin–Le Chatelier effect), strain gradient hardening phenomenon, and shear propensity during failure of the Al alloys. A composite texture consisting of a combination of Brass, Dillamore, S, and β-fiber elements in the Al alloys is found to be detrimental to their microformability. The Dillamore texture is contributed by formation of adiabatic shear bands during deformation of Al alloys.

Creep analysis of cementitious materials in seawater using a poro-chemo-mechanical model

With the rapid growth of the offshore engineering sector, studying the durability of offshore structures becomes primordial. Evaluating experimentally the coupling between mechanical and chemical degradation of the cement-based materials and structures is a challenging task because it requires tracking the evolution of the micro-mechanisms associated with the degradation in real time for long periods. To tackle this issue, a numerical approach is proposed, based on the micromechanics and the coupling between a creep-damage model and a chemical model at the microstructural scale. The seawater chemical effect on cement paste is simulated by considering the penetration fronts of the aggressive water and the attack by layers in the material. The aim of this study is to provide a tool for the rapid mechanical evaluation of the offshore structures and therefore a tool that can be used for the optimization and the development of durable marine constructions. The results highlight the competition between protective and damaged layers formed due to seawater attack, and that the global mechanical behaviour strongly depends on the chemically modified phases in the cement paste.

Role of silicon on formation and growth of intermetallic phases during rapid Fe–Zn alloying reaction

The study of liquid metal embrittlement in Fe–Zn systems is challenging because of the high temperature and vapor pressure of Zn, which hinders in-situ investigations with sufficiently high spatial resolution. This is typically associated with subsecond processing steps and the coexistence of a solid substrate and a liquid Zn phase, which renders direct observations at the microstructural scale difficult. In this study, we comprehensively investigate the reactions occurring during the rapid heating and cooling stages of Fe–Zn systems using synchrotron X-ray diffraction. The phase transformation is analyzed for specimens with different interfacial structures, with focus on changes in the coating microstructure above and below the peritectic temperature (782 °C) of the Fe–Zn system. Advanced high-strength steel (AHSS) variants with 1.5 wt% Si content show a prominent destabilizing effect at the onset of Fe–Zn intermetallic compound formation and a simultaneous deceleration of the liquid Zn depletion rate compared with other AHSS alloys containing 0 wt% Si. Furthermore, the addition of Si suppresses the formation of the Γ phase, which is due to turbulence in the outburst Zn at temperatures above 773 K. Consequently, the fraction of Γ phase compounds with accumulated Zn deceases as the exposure time of the liquid Zn to the ferritic matrix increases owing to the solute redistribution of Si in the liquid Zn during rapid heating. Meanwhile, the absence of silicon in the substrate causes the formation of a ζ phase with a low melting point, which delays the formation of liquid Zn via an increase in the melting point of the Zn layer in the early stage of heating. Additionally, the amount of residual liquid Zn decreases due to the rapid depletion of Zn during the liquid initiation stage via an equilibrium Fe/Zn binary phase transformation. The results of this study provide a deeper understanding of the Fe–Zn intermetallic phase transformation and the sensitivity to liquid metal embrittlement of third-generation AHSSs based on silicon content.

Friction measurement of modified Polydimethylsiloxane(PDMS) surfaces inspired by Malayopython Reticulatus

The lack of limbs on snakes enables its ventral scales to be in almost constant contact with the substrate. Their skin is presumably adapted to generate high and low friction to slither. This frictional characteristics in snakes were hypothesized to be contributed by the be tooth-shaped or denticle-like microstructures found on the snake ventral scales. The frictional properties of the microstructures found on snake ventral scales was studied and its feasibility as an inspiration for surface modifications was observed. This study was carried out to analyze the frictional anisotropy exhibit by the snake ventral scale microstructures and also how it changes the frictional properties of the PDMS surface when the microstructures are replicated on to it. The PDMS embedded-elastomeric stamping method was used in this experiment to replicate the snake ventral scales onto the PDMS. Based on the data collected the microstructures on the snake ventral scales does exhibit frictional anisotropy. The PDMS with replicated snakeskin microstructures displays higher COF compared to PDMS with smooth surface. When sliding on most types of surfaces, the COF of real snakeskin and replicated snakeskin is higher if the surface is semi wet. Whereas for smooth PDMS the COF is lower when the surfaces are semi wet. Generally, from both experiments, when the replicated snakeskin is sliding on the surface in the lateral direction, it is observed that the COF is the lowest followed by the caudal then the rostral direction.

Physics-informed machine-learning model of temperature evolution under solid phase processes

We model temperature dynamics during Shear Assisted Proccess Extrusion (ShAPE), a solid phase process that plasticizes feedstock with a rotating tool and subsequently extrudes it into a consolidated tube, rod, or wire. Control of temperature is critical during ShAPE processing to avoid liquefaction, ensure smooth extrusion, and develop desired material properties in the extruded products. Accurate modeling of the complicated thermo-mechanical feedbacks between process inputs, material temperature, and heat generation presents a significant barrier to predictive modeling and process design. In particular, connecting micro-structural scale mechanisms of heat generation to macro-scale predictions of temperature can become computationally intractable. In this work we use a neural network (NN) model of heat generation to bridge this gap, by combining it with a simplified model of the temperature dynamics due to conduction and convection to capture the macro scale evolution of temperature. We inform the construction of the NN heat generation model using crystal plasticity simulations at the micro-structural scale to model the effects of process inputs on generation of heat. We achieved close fits of the temperature dynamics model to a diverse experimental data-set. Further, the relationships learned by the NN model between process inputs and heat generation showed qualitative agreement with those predicted by crystal plasticity simulations.

Microstructure characteristics, stress–strain behaviour, fresh properties, and mechanical performance of recycled plastic aggregate self-compacting concrete modified with nano-silica

Reuse of recycled plastic in the construction industry is a novel approach instead of landfilling. However, the utilization of recycled plastic aggregates (RPA) aggravated the majority of concrete properties. In previous investigations, different techniques such as surface treatment of RPAs were utilized to reduce the negative influence of the RPAs on the concrete performance. Research regarding the improvement of RPA self-compacting concrete (SCC) properties by the addition of nano-silica particles (NS) is scarce. Therefore, the current study aims to experimentally investigate the properties of the SCC-incorporated RPAs modified with NS. The experimental program contained sixteen different mixtures which were subdivided into three stages. In the first stage, the effect of NS addition on the performance of SCC mixtures was evaluated. Moreover, the effect of different percentages of RPAs was investigated in the second phase. In the third stage, the optimum percentage of NS particles found in the first stage was utilized to improve the performance of SCC mixtures which aggravated in the second stage. The total binder content for all mixtures was 500 kg/m3 which contained 70 % of cement, 20 % of ground granulated blast furnace slag (GGBFS) and 10 % silica fume. In the first stage the cement was replaced by 1 %, 2 %, and 3 % NS particles, while, in the second stage, the natural fine aggregate (NFA) was replaced by RPAs at six volume fractions (5 %, 10 %, 15 %, 20 %, 30 %, and 40 %). The fresh behaviour of all SCC mixtures was investigated to assess the flowability, filling ability, passing ability, and cohesiveness of the mixtures. The mechanical behaviour was evaluated for compressive strength, splitting tensile strength, modulus of elasticity, flexural strength, and stress–strain behaviour. Moreover, the microstructure characteristics were investigated to illustrate the modifications that occurred in the microstructure scale. The results indicated that the addition of an optimum percentage of NS particles can significantly restore most properties of RPASCC which were degraded due to the addition of RPAs. This technique can help the construction industry to safely use the RPAs in the SCC mixtures without concern about their negative impact on concrete performance.

Nickel oxide scale microstructure and accelerated growth in combustion flue gas: Effect of ash particles

Model Ni-25Cr and Ni-25Cr-2Mn-1Si (wt%) alloys coated with an industrial fly ash were exposed to a wet CO2 gas at 750 °C. It was found that the outer thermally-grown NiO scale encapsulated ash particles at an accelerated rate. TEM combined with TKD analysis revealed that nano structured NiO grains on the ash surface contributed to the observed NiO encapsulating effect.

Micromechanical origin for the wide range of strength-ductility trade-off in metastable high entropy alloys†

Through different annealing temperatures and times, it is reported here that interstitial metastable high entropy alloys (HEAs) can exhibit a wide range of strength-ductility trade-offs. The underlying mechanisms were investigated via in situ neutron diffraction, electron backscattered diffraction, and electron channel contrast imaging analyses. These techniques revealed that the phase transformation process could be tuned by various annealing processes, resulting in different degrees of load partitioning and sharing among different phases and grain families on the commensurate microstructural length scales. Therefore, the microstructures generated by thermal treatments and phase transformation from face-centered-cubic to hexagonal-close-packed phases could efficiently improve the ductility of the studied alloys.