High-entropy alloys (HEAs) are of more chemical inhomogeneity than traditional alloys. How thermal effects perturb entropy and chemical fluctuations is a major scientific issue. In this study, selected benchmark phenomena revealed by in-situ synchrotron X-ray mapping demonstrates how local chemical gradients control temperature-dependent behaviors in HEAs. Specifically, the gradient chemical layers in the core/shell structure play an important role in the thermally-induced phase transformation of Cu15Ni35Ti50-x(HfZr)x high-entropy shape-memory alloys (HESMAs). The dendritic microstructure in Cu15Ni35Ti20(HfZr)30 exhibits the mixing enthalpy-driven pronounced composition inhomogeneity of an Ni-Hf-rich core and Cu-Zr-Ti-rich shell, demonstrated by thermodynamics calculations and second nearest-neighbor modified embedded atom method (2NN MEAM) formalism. The shell acts as an interfacial energy barrier for the stable martensitic transformation that occurred primarily in the effective Ni-Hf-rich core of the Cu15Ni35Ti20(HfZr)30. The temperature-dependent Gibbs-free energy agrees with the Cu movement, which widens the thermally-induced gradient layer of the elemental redistribution. Our findings are conducive to a potential design strategy of tailoring gradient chemical core/shell HEAs for stable high-temperature shape-memory applications

This research primarily focuses on the effect of changing electric field directions on the crystal structure of piezoelectric fibers, notably, P(VDF–TrFE) and P(VDF–TrFE–CTFE). The study also explores the deformation mechanisms of fibers at micro- and nanoscales. A significant aspect of the research involves the application of parallel and perpendicular electric fields and observation of their impact on fiber properties. In situ wide-angle X-ray diffraction (WAXD) studies are crucial for determining the nanoscale properties when the electric field orientations change. The results show that the direction of the electric field significantly affects the sign (positive or negative) of the dipole vector within the β-crystal lattice structure of the fibers. This can be attributed to the rotation of dipole vectors in response to the electric field–fiber alignment angle. Furthermore, the research identifies the crystal plane (201,111)β as exhibiting the highest magnitude of piezoelectric response strain in the β phase. The study also employs scanning electron microscopy and digital image correlation (DIC) to reveal the material's morphology and to assess fiber strain distribution at the micrometer scale under different voltages. DIC results particularly highlight that stress concentration leads to the deformation of fibers into voids, which are spaces between fibers created by electrospinning. This work comprehensively elucidates how deformation works in piezoelectric polymers by connecting large-scale changes observed in fibers through DIC and small-scale changes observed in WAXD studies presenting the piezoelectric strain responses at the crystal plane.

This work applied three machine learning (ML) models—linear regression (LR), random forest (RF), and support vector regression (SVR)—to predict the lattice parameters of the monoclinic B19′ phase in two distinct training datasets: previously published ZrO2-based shape-memory ceramics (SMCs) and NiTi-based high-entropy shape-memory alloys (HESMAs). Our findings showed that LR provided the most accurate predictions for ac, am, bm, and cm in NiTi-based HESMAs, while RF excelled in computing βm for both datasets. SVR disclosed the largest deviation between the predicted and actual values of lattice parameters for both training datasets. A combination approach of RF and LR models enhanced the accuracy of predicting lattice parameters of martensitic phases in various shape-memory materials for stable high-temperature applications.

Distributions of Eu2+ and Eu3+ do affect the optical properties. However, the substitution of the activator ions hardly perturbed the crystal structure of the host lattice. Without the differences in crystal structure, it is not trivial to develop an effective descriptor to investigate stoichiometry-dependent mechanism to explore the effects of Eu species on valence states. In this study, through x-ray nanodiffraction, x-ray fluorescence, x-ray absorption near edge structure, and x-ray excited optical luminescence, we mapped the valence state distributions of Eu species to calculate the local mixing enthalpy and entropy. The calculated thermodynamics parameters show good agreement with the optical properties. We found that Eu2+ of Eu-doped BaAl2O4 predominantly existed in a divalent state, which results in segregation phenomena of local Eu2+ and Eu3+ ions.

The present study investigates the crystallographic-texture effects on the improved fatigue resistance in the CoCrFeMnNi high-entropy alloys (HEAs) with the full-size geometry of the American Society for Testing and Materials (ASTM) Standards E647-99. We exploited X-ray nano-diffraction (XND) mapping to characterize the crystal-deformation levels ahead of the crack tip after stress unloading under both constant- and tensile-overloaded-fatigue conditions. The crack-tip blunting-induced much higher deformation level was concentrated surrounding the crack-tip which delays the fatigue-crack growth immediately after a tensile overload. The predominant deformation texture orientation in the Paris regime was investigated, using electron backscatter diffraction (EBSD) and orientation distribution function (ODF) analyses. The twinning formation-driven shear deformation gave rise to the development of the Goss-type texture within the plastic deformation regime under a tensile-overloaded-fatigue condition, which was attributed to enhance the crack deflection and thus the tensile-induced crack-growth-retardation period in the CoCrFeMnNi HEA. Our new findings address the quantitative discrepancy found in our earlier work.

To minimize the stress shielding effect of metallic biomaterials in mimicking bone, the body-centered cubic (bcc) unit cell-based porous CoCrMo alloys with different, designed volume porosities of 20, 40, 60, and 80% were produced via a selective laser melting (SLM) process. A heat treatment process consisting of solution annealing and aging was applied to increase the volume fraction of an ε-hexagonal close-packed (hcp) structure for better mechanical response and stability. In the present study, we investigated the impact of different, designed volume porosities on the compressive mechanical properties in as-built and heat-treated CoCrMo alloys. The elastic modulus and yield strength in both conditions were dramatically decreased with increasing designed volume porosity. The elastic modulus and yield strength of the CoCrMo alloys with a designed volume porosity of 80% exhibited the closest match to those of bone tissue. Different strengthening mechanisms were quantified to determine their contributing roles to the measured yield strength in both conditions. The experimental results of the relative elastic modulus and yield strength were compared to the analytical and simulation modeling analyses. The Gibson–Ashby theoretical model was established to predict the deformation behaviors of the lattice CoCrMo structures.

The present work extends the examination of selective laser melting (SLM)-fabricated 15-5 PH steel with the 8%-transient-austenite-phase towards fully-reversed strain-controlled low-cycle fatigue (LCF) test. The cyclic-deformation response and microstructural evolution were investigated via in-situ neutron-diffraction measurements. The transient-austenite-phase rapidly transformed into the martensite phase in the initial cyclic-hardening stage, followed by an almost complete martensitic transformation in the cyclic-softening and steady stage. The compressive stress was much greater than the tensile stress at the same strain amplitude. The enhanced martensitic transformation associated with lower dislocation densities under compression predominantly governed such a striking tension-compression asymmetry in the SLM-built 15-5 PH.

The extraordinary dynamics of microstructures, such as various dislocations, stacking faults, twinning, and polymorphism transformations, dominate the mechanical performance of high-entropy alloys. To reveal the phase transformation kinetics, we precisely detect the microstructure evolution in CoCrFeMnNi high-entropy alloy (HEA) and CrFeNi medium-entropy alloy (MEA) subjected to high-pressure compression using in situ angular-dispersive synchrotron X-ray diffraction. We find that controlling the initial microstructural state using cold-rolling can significantly reduce the stacking fault energy of CoCrFeMnNi and CrFeNi alloys, which results in lower onset pressures for phase transformations. The microstructure-induced stacking-fault energy reduction facilitates the formation of twins, which can act as nucleation sites for hexagonal close-packed (HCP) phase formation and recrystallization. The microstructure evolution-driven deviatoric deformation mechanism of CoCrFeMnNi HEA and CrFeNi MEA under quasi-hydrostatic compression is explored. Beyond the FCC phase, twinning in the HCP phase of CoCrFeMnNi alloy under high pressure is observed for the first time. This implies that the deformation mechanism of CoCrFeMnNi HEAs in the HCP phase is dominated by twinning-induced plasticity, which is verified using transmission electron microscopy.

In this research, we systematically investigated equiatomic CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs). Both of these HEA systems are single-phase, face-centered-cubic (FCC) structures. Specifically, we examined the tensile response in as-cast quaternary CoCrFeNi and quinary CoCrFeMnNi HEAs at room temperature. Compared to CoCrFeNi HEA, the elongation of CoCrFeMnNi HEA was 14% lower, but the yield strength and ultimate tensile strength were increased by 17% and 6%, respectively. The direct real-time evolution of structural defects during uniaxial straining was acquired via in situ neutron-diffraction measurements. The dominant microstructures underlying plastic deformation mechanisms at each deformation stage in as-cast CoCrFeNi and CoCrFeMnNi HEAs were revealed using the Convolutional Multiple Whole Profile (CMWP) software for peak-profile fitting. The possible mechanisms are reported.

The role of residual stress is critical, particularly for machine tools demanding accuracy below 1 µm. Although minor stresses are subjected to a tiny area, the applied force can cause devastating distortions on the precision components at this length scale. In this research, we systematically investigated the residual stress in a stress frame of the gray iron used in machine tools using synchrotron X-ray and neutron sources. Through the combination of these techniques, the residual stresses on the surface, inside the bulk, and in average were presented. Comprehensive analysis results shed light on the vibratory stress relief technique, which reduced the residual stresses and stabilized them, even materials undergoing cycling heating. Although compressive stresses are not effectively reduced, this technique is useful in improving the mechanical stability of the materials in machine tools.

In this study, we explored the elevated-temperature stability of the medium- and high-entropy alloys for metallurgical processes and applications. Because the extraordinary mechanical properties of medium- and highentropy alloys are strongly correlated with their distinct microstructural developments, we applied the latest insitu high-resolution synchrotron X-ray diffraction technique to trace the real-time microstructural evolutions of these alloys during annealing and recrystallization processes. We resolved the convolution information for crystallite size, dislocation characteristics, and planar fault probabilities to examine the microstructural stability and differences between CrFeNi and CoCrFeMnNi alloys. The most significant difference is the grain coarsening of the two alloys subjected to heating from 600 degrees C to 800 degrees C. Specifically, the dominant dislocation type of medium- and high-entropy alloys switched from screw to mixed screw-edge after 700 degrees C. Meanwhile, the screening of dislocation-induced strain-fields of both alloys became stronger during annealing. Our major findings will be useful for the welding and additive manufacturing medium- and high-entropy alloys.

The combination of multiple-principal element materials, known as high-entropy materials (HEMs), expands the multi-dimensional compositional space to gigantic stoichiometry. It is impossible to afford a holistic approach to explore each possibility. With the advance of the materials genome initiative and characterization technology, a high-throughput (HT) approach is more reasonable, especially to identify the specified functions for the new HEMs development. There are three major components for the HT approach, which are the computational tools, experimental tools, and digital data. This article reviews both the materials informatics and experimental approaches for the HT methods. Applications of these tools on composition-varying samples can be used to obtain stoichiometry effectively and phase-structure-property relationships efficiently for the materials-property database establishment. They can also be used in conjunction with machine learning (ML) to improve the predictability of models. These ML tools will be an essential part of HT approaches to develop the new HEMs. The ML-developed HEMs together with ML-created other materials are positioned in this manuscript for future HEMs advancement. Comparing all the reviewed properties, the hierarchical microstructures together with the heterogeneous grain sizes show the highest potential to apply ML for new HEMs, which needs HT validations to accelerate the development. The promising potential and the database from the HEMs exploration would shed light on the future of humanity building from the scratch of Mars regolith.

Fine melt pool (FMP), coarse melt pool (CMP), and heat affected zone (HAZ) are generally observed in the additive manufactured AlSi10Mg alloys. In this study, we demonstrated that the yield strength can be estimated by the combination of the sizes and volume fractions of FMP, CMP, HAZ together with the second-phase hardening. Two different AlSi10Mg alloys fabricated via powder bed fusion (PBF) process were prepared to examine the lattice strain evolution of constituent phases during uniaxial tensile loading via in-situ neutron diffraction measurements. The horizontally-built (Hz-built) exhibited a much better yield and tensile strength as well as elongation compared to the vertically-built (Vt-built) AlSi10Mg alloy. The stress partitioning from Al matrix to reinforcement Si was obtained during plastic deformation regime in both alloys. However, a greater capability of enduring high load of Si and a load transferring back to the ductile Al matrix found in the latter period of plastic deformation are responsible for better tensile properties in the Hz-built AlSi10Mg alloy. We reported empirical strength quantification based on the sizes and ratios of FMP, CMP, and HAZ together with the possible failure mode to prevent early fracture in the additive manufactured alloys.

The coaxial core/shell composite electrospun nanofibers consisting of relaxor ferroelectric P(VDF-TrFE-CTFE) and ferroelectric P(VDF-TrFE) polymers are successfully tailored towards superior structural, mechanical, and electrical properties over the individual polymers. The core/shell-TrFE/CTFE membrane discloses a more prominent mechanical anisotropy between the revolving direction (RD) and cross direction (CD) associated with a higher tensile modulus of 26.9 MPa and good strength-ductility balance, beneficial from a better degree of nanofiber alignment, the increased density, and C-F bonding. The interfacial coupling between the terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for comparable full-frequency dielectric responses between the core/shell-TrFE/CTFE and pristine terpolymer. Moreover, an impressive piezoelectric coefficient up to 50.5 pm/V is achieved in the core/shell-TrFE/CTFE composite structure. Our findings corroborate the promising approach of coaxial electrospinning in efficiently tuning mechanical and electrical performances of the electrospun core/shell composite nanofiber membranes-based electroactive polymers (EAPs) actuators as artificial muscle implants.

The effect of grain size on strain-controlled low-cycle fatigue (LCF) properties in the CoCrFeMnNi high-entropy alloys (HEAs) was investigated towards the distinct microstructural developments during cyclic loading at a strain amplitude of +/- 1.0%. A much more prominent secondary cyclic hardening (SCH) behavior at the final deformation stage was observed in the fine-grained (FG, 18 mu m) than in the coarse-grained (CG, 184 mu m) CoCrFeMnNi. In-situ neutron-diffraction and microscopic examination, strongly corroborated by molecular dynamic (MD) simulations, indicated that dislocation activities from planar slip to wavy slip-driven subgrain structures within the grains acted as the primary cyclic-deformation behaviors in the FG CoCrFeMnNi. Differently observed in the cyclic behavior of the CG CoCrFeMnNi was due to a transition from the planar dislocation slip to twinning. Our findings suggested that the fatigue-resistant HEAs can be designed via tuning the microstructure with an optimal range of grain size at a specific strain amplitude. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In this study, we optimized the geometry and composition of additive-manufactured pedicle screws. Metal powders of titanium-aluminum-vanadium (Ti-6Al-4V) were mixed with reactive glass-ceramic biomaterials of bioactive glass (BG) powders. To optimize the geometry of pedicle screws, we applied a novel numerical approach to proposing the optimal shape of the healing chamber to promote biological healing. We examined the geometry and composition effects of pedicle screw implants on the interfacial autologous bone attachment and bone graft incorporation through in vivo studies. The addition of an optimal amount of BG to Ti-6Al-4V leads to a lower elastic modulus of the ceramic-metal composite material, effectively reducing the stress-shielding effects. Pedicle screw implants with optimal shape design and made of the composite material of Ti-6Al-4V doped with BG fabricated through additive manufacturing exhibit greater osseointegration and a more rapid bone volume fraction during the fracture healing process 120 days after implantation, per in vivo studies.

An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both metallic systems. However, as obtained from the diffraction-peak-width evolution, the underneath deformation mechanisms are quite different. The CoCrFeMnNi HEA exhibits distinct lattice strain and microstructure responses under tension-compression cyclic loadings.

A N95 face-piece respirator and a 3M air filter composed of non-woven polypropylene filter material were investigated for their multi-scale microstructure and resulting filtration performance. Filtration mechanisms of each system are found and quantified. Both media showed a gradually decrease of the most penetrating particle size with respect to an increase in face velocity or surface charge density. Increasing the face velocity and porosity dramatically degraded the collection efficiency in the 3M filter rather than in the N95 system. We exploited three-dimensional X-ray tomography to characterize the morphological and geometrical properties of the fiber arrangement and deposition of aerosol on the fiber surface. Tuning the most predominant material parameters to achieve a precedence in lower pressure drop or higher collection efficiency in a specifically captured particle size range is of great requisite to a peculiar application of the filter media.

Unalloyed nickel aluminide has important applications but lacks ductility at room temperature. In this study, iron-added nickel aluminide alloys exhibit plasticity enhancement. The nickel aluminide alloys are prepared with different iron contents (0, 0.25, and 1 at%) to study their plasticity. The indentation-induced deformed areas are mapped by the synchrotron X-ray diffraction to compare their plastic zones. A complimentary tight binding calculation and generalized embedded atom method demonstrate how the Fe-addition enhances the plasticity of the iron-added nickel aluminide alloys.