Chemical Inhomogeneity Research Articles

Effect of microstructure on the pitting susceptibility of a martensitic-ferritic stainless steel: A corrosion-metallurgical study

The relationship between microstructure, composition and the localized corrosion resistance of a low carbon Cr-Ni-Mo martensitic-ferritic stainless steel was investigated. Four heat treatments were selected to examine the effect of varying tempered Martensitic-Ferritic microstructures on localized corrosion susceptibility. The pitting potential for each heat treatment was determined in deaerated 192 g/L NaCl electrolyte saturated with CO2 (pH: 3.8) at 65 °C. Austenite reversion and other microstructural transformations associated with tempering had a detrimental effect on the pitting potential. The resulting chemical and structural inhomogeneities decreased the pitting potential.

Analysis of structural and chemical inhomogeneity of thin films developed on ferrite grains by color etching with Beraha-I type etchant with spectroscopic ellipsometry and XPS

The structural and chemical homogeneity of the developed thin film upon color etching a low-carbon steel specimen with Beraha-I type color etchant was investigated by spectroscopic ellipsometry and electron backscatter diffraction examinations. The obtained layer thickness maps showed a good correlation with the crystallographic orientation of the individual ferrite grains, corresponding well with previous studies that found a relation between etching and layer build-up speeds and the <100>, <111> directions. However, the refractive index map also showed a dependence on the grain orientation, which contradicts previous models that treat the developed interfering layer as a homogenous material with a constant refractive index and chemical composition. Scanning ellipsometry and X-ray photoelectron spectroscopy measurements confirmed that the chemical composition and refractive index of the developed layer are inhomogeneous both along the surface and the thickness of the film. It was shown that the developed layer consists of mainly oxides and sulfides and that the oxygen content decreases, while the Fe content increases along the normal direction from the surface of the film, in good agreement with the increasing refractive index. The observed differences can be related to the different etching speeds of the ferrite grains (Fe dissolution rate), depending on their orientation.

Tailoring the chemical heterogeneity of Mn-modified 0.75BiFeO3-0.25BaTiO3 ceramics for piezoelectric sensor applications

The Mn-modified 0.75BiFeO3-0.25BaTiO3 (75BFBTMn) piezoelectric ceramic possesses a high depolarization temperature of 500 °C and a large piezoelectric coefficient of 110 pC/N, showing the potential for high temperature piezoelectric sensors. However, 75BFBTMn ceramic usually suffers dielectric degradation and abrupt drop of piezoelectric coefficient in the range of 300 °C to 500 °C. Combined the high-energy synchrotron X-ray diffraction analysis with Backscatter-SEM results, it is demonstrated that the electrical thermal instability is owing to the existence of chemical inhomogeneity. The Air-annealing treatment is able to decrease the volume fraction of pseudo-cubic phase and the lattice distortion, removes the chemical inhomogeneity in the grain and free Bi2O3 at grain boundary, and then eliminates dielectric anomalies and piezoelectric degradation with temperature. These results indicate that air-annealing is a simple but effective method to eliminate the chemical inhomogeneity in 75BFBTMn ceramics, thereby improving the property thermal stability for high temperature piezoelectric sensor applications.

Constraining the original composition of the gas forming first-generation stars in globular clusters

ABSTRACT Disentangling distinct stellar populations along the red-giant branches (RGBs) of globular clusters (GCs) is possible by using the pseudo-two-colour diagram dubbed chromosome map (ChM). One of the most intriguing findings is that the so-called first-generation (1G) stars, characterized by the same chemical composition of their natal cloud, exhibit extended sequences in the ChM. Unresolved binaries and internal variations in helium or metallicity have been suggested to explain this phenomenon. Here, we derive high-precision Hubble Space Telescope photometry of the GCs NGC 6362 and NGC 6838 and build their ChMs. We find that both 1G RGB and main-sequence (MS) stars exhibit wider ChM sequences than those of second-generation (2G). The evidence of this feature even among unevolved 1G MS stars indicates that chemical inhomogeneities are imprinted in the original gas. We introduce a pseudo-two-magnitude diagram to distinguish between helium and metallicity, and demonstrate that star-to-star metallicity variations are responsible for the extended 1G sequence. Conversely, binaries provide a minor contribution to the phenomenon. We estimate that the metallicity variations within 1G stars of 55 GCs range from less than [Fe/H]∼0.05 to ∼0.30 and mildly correlate with cluster mass. We exploit these findings to constrain the formation scenarios of multiple populations showing that they are qualitatively consistent with the occurrence of multiple generations. In contrast, the fact that 2G stars have more homogeneous iron content than the 1G challenges the scenarios based on accretion of material processed in massive 1G stars on to existing protostars.

On the Impact of Additive Manufacturing Processes on the Microstructure and Magnetic Properties of Co–Ni–Ga Shape Memory Heusler Alloys

Microstructure design allows to prevent intergranular cracking and premature failure in Co–Ni–Ga shape memory alloys. Favorable grain boundary configurations are established using additive manufacturing techniques, namely, direct energy deposition (DED) and laser powder bed fusion (L‐PBF). L‐PBF allows to establish a columnar grain structure. In the Co–Ni–Ga alloy processed by DED, a microstructure with strong ⟨001⟩ texture is obtained. In line with optimized microstructures, the general transformation behavior is essential for performance. Transition parameters such as transition temperature and thermal hysteresis depend on chemical composition, homogeneity, and presence of precipitates. However, these parameters are highly dependent on the processing method used. Herein, the first‐order magnetostructural transformation and magnetization properties of Co–Ni–Ga processed by DED and L‐PBF are compared with single‐crystalline and as‐cast material. In the alloy processed by L‐PBF, Ga evaporation and extensive formation of the ferromagnetic Co‐rich γ'‐phase are observed, promoting a very wide transformation range and large thermal hysteresis. In comparison, following DED, the material is characterized by minor chemical inhomogeneity and transition and magnetization behavior being similar to that of a single crystal. This clearly renders DED‐processed Co–Ni–Ga to become a promising candidate material for future shape memory applications.

Soft X-ray characterization of halide perovskite film by scanning transmission X-ray microscopy

Organic–inorganic metal halide perovskites (MHPs) have recently been receiving a lot of attention due to their newfound application in optoelectronic devices, including perovskite solar cells (PSCs) which have reached power conversion efficiencies as high as 25.5%. However, the fundamental mechanisms in PSCs, including the correlation of degradation with the excellent optoelectrical properties of the perovskite absorbers, are poorly understood. In this paper, we have explored synchrotron-based soft X-ray characterization as an effective technique for the compositional analysis of MHP thin films. Most synchrotron-based studies used for investigating MHPs so far are based on hard X-rays (5–10 keV) which include various absorption edges (Pb L-edge, I L-edge, Br K-edge, etc.) but are not suited for the analysis of the organic component in these materials. In order to be sensitive to a maximum number of elements, we have employed soft X-ray-based scanning transmission X-ray microscopy (STXM) as a spectro-microscopy technique for the characterization of MHPs. We examined its sensitivity to iodine and organic components, aging, or oxidation by-products in MHPs to make sure that our suggested method is suitable for studying MHPs. Furthermore, methylammonium triiodide with different deposition ratios of PbI2 and CH3NH3I (MAI), and different thicknesses, were characterized for chemical inhomogeneity at the nanoscale by STXM. Through these measurements, we demonstrate that STXM is very sensitive to chemical composition and homogeneity in MHPs. Thus, we highlight the utility of STXM for an in-depth analysis of physical and chemical phenomena in PSCs.

Correlation between thickness dependent nanoscale structural chemistry and superconducting properties of ultrathin epitaxial NbN films

NbN-based superconductors have attracted interest for superconducting circuits, quantum computation and high frequency devices. The superconducting properties of NbN films are predominately reliant on the microstructure, therefore, an atomic-level understanding of the structure-chemistry is required to achieve high quality epitaxial NbN films. Here, the thickness-dependent superconducting properties of NbN films (5, 10, and 50 nm) within NbN/AlN/Al2O3 heterostructures are investigated. NbN and AlN were epitaxially grown by an industrial scale physical vapor deposition technique. The role of nanoscale chemistry on the ultrathin NbN superconducting film is investigated at the atomic level for the first time via atom probe tomography, providing three-dimensional atomic distribution, chemical homogeneity, effect of impurities, specially, in secondary phase formations and interfacial abruptness. The NbN film with 5 nm of thickness demonstrates a superconducting transition temperature of 11.2 K as compared to 50 nm NbN films with a transition temperature of 15.3 K. These thickness dependent variation of superconducting properties are associated with the chemical inhomogeneity in terms of in-plane N:Nb distribution, secondary phase formations and NbN/AlN interfacial abruptness as a function of the NbN films thicknesses. The analysis depicts the interplay between the surface/interface and the superconducting properties of ultrathin NbN films. These results provide insights on material design and growth that will enable the development of optimized superconducting NbN films for quantum devices.

Three-Dimensional Shape Transformation of Eu3+-Containing Polymer Films through Modulating Dynamic Eu3+-Iminodiacetate Coordination

Shape-transformative materials that can autonomously adopt three-dimensional (3D) shapes in response to environmental stimuli are of interest for the development of sensors and soft robotics. We herein report a new synthetic strategy to fabricate shape-transformable Eu3+-containing interpenetrating polymer films consisting of poly(vinyl alcohol) (PVA) and poly(3-iminodiacetate-2-hydroxypropylmethacrylate-co-acrylic acid) (P(IDHPMA-co-AA)). Given the dynamic nature of Eu3+-iminodiacetate (IDA) coordination, ink patterning and water/Fe3+ diffusion are used to generate the in-plane or z-directional heterogeneities of Eu-IDA dynamic coordination in the polymer film, respectively. The heterogeneities can be visualized by the distribution of fluorescence emission of Eu3+. When subjected to high humidity, the differences in the swelling ratio and modulus as a result of chemical inhomogeneity further drive various 3D shape morphings, including rolling, helixing, twisting, surface buckling, and folding. Shape transformation is reversible upon the removal of moisture from the polymer films. The ink concentration and environmental humidity are demonstrated to impact the shape transformation kinetics and the final 3D shape along with other geometric parameters. Our work illustrates a novel way to fabricate new-generation biomimetic actuators and sensors.

Effective boundary conditions for dynamic contact angle hysteresis on chemically inhomogeneous surfaces

Recent experiments (Guan et al., Phys. Rev. Lett., vol. 116, issue 6, 2016a, p. 066102; Guan et al., Phys. Rev. E, vol. 94, issue 4, 2016b, p. 042802) showed many interesting phenomena on dynamic contact angle hysteresis while there is still a lack of complete theoretical interpretation. In this work, we study the time averaging of the apparent advancing and receding contact angles on surfaces with periodic chemical patterns. We first derive a new Cox-type boundary condition for the apparent dynamic contact angle on homogeneous surfaces using the Onsager variational principle. Based on this condition, we propose a reduced model for some typical moving contact line problems on chemically inhomogeneous surfaces in two dimensions. Multiscale expansion and averaging techniques are employed to approximate the model for asymptotically small chemical patterns. We obtain a quantitative formula for the averaged dynamic contact angles. It describes explicitly how the advancing and receding contact angles depend on the velocity and the chemical inhomogeneity of the substrate. The formula is a coarse-graining version of the Cox-type boundary condition on inhomogeneous surfaces. Numerical simulations are presented to validate the analytical results. The numerical results also show that the formula characterizes well the complicated behaviour of dynamic contact angle hysteresis observed in the experiments.

Microstructural evolution and effect of heat treatment on the precipitation and mechanical behavior of Al0.7CoCrFeNi alloy

The microstructural features and promising properties exhibited by Al0.7CoCrFeNi have led to extensive studies on the alloy. The current work discusses the microstructural evolution, thermal stability and mechanical behavior of the alloy. CALPHAD studies predicated the alloy to be near eutectic with pro-eutectic BCC and eutectic FCC and BCC/B2. However, experimental studies displayed the FCC phase to evolve from a high-temperature B2. Interfacial energy, chemical inhomogeneity and cooling rate were attributed to play a key role in the microstructural evolution and phase stability. Heat treatment resulted in the dissolution of BCC and the formation of Al-Ni-rich B2 phase. During solidification and heat treatment, Widmanstätten FCC formed and coarsened via superledge mechanism. Further, thermal exposure resulted in lamellar instability and localized globularization of the B2 phase. The heat-treated alloy displayed excellent resistance to thermal softening when compared to the cast alloy. Further, the thermally exposed alloy exhibited a superior work hardening rate.

Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189 b

The temperature of an atmosphere decreases with increasing altitude, unless a shortwave absorber exists that causes a temperature inversion. Ozone plays this role in the Earth`s atmosphere. In the atmospheres of highly irradiated exoplanets, shortwave absorbers are predicted to be titanium oxide (TiO) and vanadium oxide (VO). Detections of TiO and VO have been claimed using both low and high spectral resolution observations, but later observations have failed to confirm these claims or overturned them. Here we report the unambiguous detection of TiO in the ultra-hot Jupiter WASP-189b using high-resolution transmission spectroscopy. This detection is based on applying the cross-correlation technique to many spectral lines of TiO from 460 to 690 nm. Moreover, we report detections of metals, including neutral and singly ionised iron and titanium, as well as chromium, magnesium, vanadium and manganese (Fe, Fe+, Ti, Ti+, Cr, Mg, V, Mn). The line positions of the detected species differ, which we interpret as a consequence of spatial gradients in their chemical abundances, such that they exist in different regions or dynamical regimes. This is direct observational evidence for the three-dimensional thermo-chemical stratification of an exoplanet atmosphere derived from high-resolution ground-based spectroscopy.

PEGylation of silver nanoparticles by physisorption of cyclic poly(ethylene glycol) for enhanced dispersion stability, antimicrobial activity, and cytotoxicity

Silver nanoparticles (AgNPs) are practically valuable in biological applications. However, no steady PEGylation has been established, which is essential for internal use in humans or animals. In this study, cyclic PEG (c-PEG) without any chemical inhomogeneity is physisorbed onto AgNPs to successfully PEGylate and drastically enhance the dispersion stability against physiological conditions, white light, and high temperature. In contrast, linear HO–PEG–OH and MeO–PEG–OMe do not confer stability to AgNPs, and HS–PEG–OMe, which is often used for gold nanoparticles, sulfidates the surface to considerably degrade the properties. TEM shows an essentially intact nanostructure of c-PEG-physisorbed AgNPs even after heating at 95 °C, while complete disturbance is observed for other AgNPs. Molecular weight- and concentration-dependent stabilization by c-PEG is investigated, and DLS and ζ-potential measurements prove the formation of a c-PEG layer on the surface of AgNPs. Furthermore, c-PEG-physisorbed AgNPs exhibit persistent antimicrobial activity and cytotoxicity.

News from Gaia on σ Ori E: A case study for the wind magnetic braking process

Context.σ Ori E, a massive helium B-type star, shows high surface rotation and a strong surface magnetic field, potentially challenging the process of wind magnetic braking. Aims. The Gaia satellite provides an accurate distance to σ Ori E and confirms its membership to the σ Ori cluster. We account for these two key pieces of information in order to investigate whether single star models can reproduce the observed properties of σ Ori E and provide new estimates for its metallicity, mass, and age. Methods. We computed rotating stellar models accounting for wind magnetic braking and magnetic quenching of the mass loss. We considered two metallicities (Z = 0.014, with a helium mass fraction Y = 0.273 and Z = 0.020 with Y = 0.266), four initial masses between 8 and 9 M⊙, three initial rotations between 250 and 450 km s−1, and three initial surface equatorial magnetic field between 3 and 7 kG. Differential rotation is assumed for the internal rotation in all models. We looked for models simultaneously accounting for the observed radius, position in the HR diagram, surface velocity, and braking timescale. Results. We obtain that σ Ori E is a very young star (age less than 1 Myr) with an initial mass of around 9 M⊙, a surface equatorial magnetic field of around 7 kG, and a metallicity Z (mass fraction of heavy elements) of around 0.020. No solution is obtained with the present models for a metallicity of Z = 0.014. The initial rotation of the models fitting σ Ori E is not highly constrained and could be anywhere in the range studied here. Because of its very young age, models predict no observable changes of the surface abundances due to rotational mixing. Conclusions. The simultaneous high surface rotation and high surface magnetic field of σ Ori E may simply be a consequence of its young age. This young age implies that the processes responsible for producing the chemical inhomogeneities that are observed at its surface should be rapid. Therefore, for explaining the properties of σ Ori E, there is no necessity to invoke a merging event, although such a scenario cannot be discarded. Other stars (HR 5907, HR 7355, HR 345439, HD 2347, CPD –50°3509) showing similar properties to σ Ori E (fast rotation and strong surface magnetic field) may also be very young stars, although determination of the braking timescales is needed to confirm such a conclusion.

Metalloid substitution elevates simultaneously the strength and ductility of face-centered-cubic high-entropy alloys

Recently-developed high-entropy alloys (HEAs) containing multiple principal metallic elements have extended the compositional space of solid solutions and the range of their mechanical properties. Here we show that the realm of possibilities can be further expanded through substituting the constituent metals with metalloids, which are desirable for tailoring strength/ductility because they have chemical interactions and atomic sizes distinctly different from the host metallic elements. Specifically, the metalloid substitution increases local lattice distortion and short-range chemical inhomogeneities to elevate strength, and in the meantime reduces the stacking fault energy to discourage dynamic recovery and encourage defect accumulation via partial-dislocation-mediated activities. These impart potent dislocation storage to improve the strain hardening capability, which is essential for sustaining large tensile elongation. As such, metalloid substitution into HEAs evades the normally expected strength-ductility trade-off, enabling an unusual synergy of high tensile strength and extraordinary ductility for these single-phase solid solutions.

Tailored tensile properties of CoCrNi medium entropy alloy by tuning the elemental distribution

High/medium entropy alloys (HEAs/MEAs), emerged as a new exciting class of materials, have inspired the exploration of the vast compositional space. Their unique multi-component feature makes the inhomogeneity of the local chemical environment appear inevitably. Compared with traditional alloys, one of the decisive advantages of HEAs/MEAs is the tunability of their inhomogeneous elemental distribution, which holds promise for obtaining unexpected mechanical properties. Accordingly, issues regarding the effect of chemical inhomogeneity are gradually paid more and more attention. Here, a series of comprehensive atomistic simulations on chemically inhomogeneous face-centered cubic (fcc) CoCrNi MEAs are carried out to study the effect of compositional gradient on tensile behaviors of MEA and the corresponding atomic-scale mechanisms. The simulation results on cubic single crystalline CoCrNi MEAs revealed that the local absolute concentration of each element is the primary factor affecting the tensile properties of MEAs. Dislocation nucleation is found to occur at the Cr-rich region due to the localized shear deformation induced by chemical inhomogeneity, and thus result in a decrease of tensile strength. Subsequently, based on a series of simulations on equiatomic CoCrNi nanopillars with different compositional periodicity, we found that ingenious design of compositional periodicity can improve the tensile strength and plastic deformation ability owing to the plastic strain delocalization stemming from the compositional periodicity. Thus, optimization design of chemical inhomogeneity in HEAs/MEAs can turn the disadvantages of local performance degradation into benefits through enhancing the plastic strain delocalization, which is one of the effective means to promote the strength-plasticity synergy.

Effect of varying tartaric acid to metal nitrate ratio on the structure, morphology and magnetic properties of BaZn0.2Zr0.2Fe11.6O19 samples

Here in, we report synthesis of BaZn0.2Zr0.2Fe11.6O19 hexaferrite nanoparticles through the sol-gel auto-combustion route using tartaric acid as fuel. The nature of the fuel and fuel to metal nitrate ratio plays an important role in deciding the phase purity, grain size, shape, and magnetic properties of M-type hexaferrites. The optimization of the tartaric acid to metal nitrate (TA/MN) ratio was carried out by varying TA/MN ratios (0.00, 0.50, 0.75, 1.00, 1.25, and 1.50). XRD data revealed a single-phase M-type in samples synthesized using TA/MN ratio 0.50, 0.75, and 1.00 and the presence of α-Fe2O3 as an impurity phase beyond 1.00 TA/MN ratio and in a standard sample (TA/MN ratio is 0.00) both α-Fe₂O₃ and BaFe2O4 were found. FESEM micrographs revealed grain size continuously increases from 0.50 to 1.25 TA/MN ratio and decreases afterward for 1.50 TA/MN ratio. Magnetic measurements confirm that all the samples exhibit ferromagentic ordering. However, a kink along with wasp waist shape was observed in the samples synthesized using TA/MN ratio 0.00, 0.50, and 0.75 which may be due to presence of secondary phases/impurites and chemical inhomogeneity. The Hc was found to be minimum at 1.25 TA/MN ratio whereas Mr and Ms were found to be maximum at 1.00 TA/MN ratio. The optimum TA/MN ratio was found to be 1.00. These materials could be suitable for microwave absorber and magnetic recording applications due to their high Ms and low Hc values.

In Situ Infrared Micro and Nanospectroscopy for Discharge Chemical Composition Investigation of Non‐Aqueous Lithium–Air Cells (Adv. Energy Mater. 45/2021)

Li–Air Batteries In article number 2101884, Gustavo Doubek and co-workers report the use of multi-scale FTIR (Micro-Nano) to track the chemical evolution and inhomogeneities of Li–Air batteries under a realistic atmosphere. The study combines Synchrotron Infrared Nano-Spectroscopy over distinct spots in the electrode with micro-sized FTIR showing high sensitivity for chemical changes, highlighting a decoupling of composition with discharge rate and a fast electrolyte degradation process.

ОЦЕНКА ДЕФЕКТОВ ПОВЕРХНОСТИ ИЗДЕЛИЙ С ПОМОЩЬЮ ЦИФРОВЫХ ТЕХНОЛОГИЙ

The suggested approach provides an opportunity under the conditions of enterprises to give a comprehensive view of products defects and functional coatings imperfections. The application of the computer program developed in the Microsoft Visual Studio environment, which allows digital image processing of the studied surfaces to estimate the area of external defects of materials, regardless of the nature of the origin of defects and the method of image acquisition, is proved.&#x0D; Research methods. Digital images of metal surfaces and coatings obtained by energy dispersive microanalysis, electron and optical microscopy have been tested.&#x0D; Research results and novelty. The possibility of using the program for evaluation of surface bands with local chemical and morphological inhomogeneities, determination of the porosity of materials is shown. The possibility of express evaluation of digital images of objects at macro-, meso- and microstructural levels for automated diagnostic control of surface defects within 1-2 seconds is implemented. Disaggregation of brightness, texture and color components of the image significantly increases the speed and efficiency of image processing structures.&#x0D; Conclusions: The proposed program is versatile, does not require special user skills and serves as a convenient tool for analyzing and controlling the quality of objects of various physico-chemical nature. The results of the study indicate that the application of the developed computer program makes effective quantitative calculation of the area of local defects, areas of distribution of chemical elements, various inclusions, surface porosity of products and coatings possible.

Fundamental parameters of the Ap-stars GO And, 84 UMa, and κ Psc

Aims. The aim of this work is to determine fundamental parameters of three Ap stars, GO And (HD 4778), κ Psc (HD 220825), and 84 UMa (HD 120198), using spectroscopic techniques. By analysing these stars, we complete the sample of Ap stars for which fundamental parameters have additionally been derived by means of interferometry. This enables a cross-comparison of results derived by direct and indirect methods. Methods. Our study is based on the analysis of high-resolution spectra with a high signal-to-noise ratio that were obtained with ESPaDOnS spectrograph. We used an iterative method of fundamental parameter determinations that includes self-consistent modelling of the stellar atmosphere, taking individual abundances of chemical elements into account and subsequently fitting a theoretical spectral energy distribution to the observed distribution. The quality of the spectroscopic determinations was evaluated through a comparison with the interferometric results. Results. For all investigated stars, we determined fundamental parameters and derived chemical abundances that are typical for Ap stars. The abundances are mainly characterised by a gradual increase of heavy element atmospheric abundances from an order of magnitude for iron peak elements up to very significant excesses of 3–4 dex of the rare-earth elements relative to the solar values. The only exception is Ba, whose abundance is close to the solar abundance. There is also a significant He deficiency in the atmospheres of HD 120198 and HD 220825, whereas the He abundance in HD 4778 is close to the solar abundance. We do not find significant Fe and Cr stratification. Using these abundances, we constructed self-consistent atmospheric models for each star. The effect of the surface chemical inhomogeneity on the derived fundamental parameters did not exceed ±100 K in effective temperature, which lies within the range of errors in similar self-consistent analyses of Ap stars. Finally, we compared spectroscopically derived effective temperatures, radii, and luminosity for 13 out of 14 Ap stars in a benchmark sample with the interferometric results. While radii and luminosity agree within the quoted errors of both determinations, the spectroscopic effective temperatures are higher than the interferometric temperatures for stars with Teff &gt; 9000 K. The observed hydrogen line profiles favour the spectroscopically derived temperatures.

Designing order\u2013disorder transformation in high-entropy ferritic steels

Order–disorder transformations hold an essential place in chemically complex high-entropy ferritic steels (HEFSs) due to their critical technological application. The chemical inhomogeneity arising from mixing of multi-principal elements of varying chemistry can drive property altering changes at the atomic scale, in particular short-range order. Using density-functional theory-based linear-response theory, we predict the effect of compositional tuning on the order–disorder transformation in ferritic steels—focusing on Cr–Ni–Al–Ti–Fe HEFSs. We show that Ti content in Cr–Ni–Al–Ti–Fe solid solutions can be tuned to modify short-range order that changes the order–disorder path from BCC-B2 (Ti atomic-fraction = 0) to BCC-B2-L21 (Ti atomic-fraction > 0) consistent with existing experiments. Our study suggests that tuning degree of SRO through compositional variation can be used as an effective means to optimize phase selection in technologically useful alloys.Graphic abstract