Structure Of Alloys Research Articles

Unraveling the connection of electronic and phononic structure with mechanical properties of commercial AZ80 alloy

Magnesium alloys, particularly in the aluminum-zinc (AZ) series, are widely recognized for their remarkable strength-to-weight ratio. We performed electronic structure, lattice dynamics, and mechanical properties of the AZ80 alloy using first-principles density-functional theory. The influence of dilute alloying by Al/Zn was observed in electronic-structure of AZ80 through hybridization of Mg-(s,p) with Al-p/Zn-d states. The Allen’s electronegativity difference between Mg and Al/Zn was found to induce charge transfer mechanism that provides solid-solution strengthening and ductility, in agreement with experiments. The electronic and phononic band-structure was unfolded onto the primitive unit cell of pure Mg to provide key information related to structural distortions and disorder effects. Finally, the dynamic and mechanical stability of AZ80 were confirmed by phonons and Born-Huang criteria, respectively. Collectively, this study provides valuable insights into the fundamental properties of lightweight commercial grade AZ80, essential for application-oriented design of Mg alloys.

Preparation and Study of Ti3C2Tx MXene–Deficient In Situ Anchored Fe−Co Alloy Nanoparticle Electrocatalyst for Hydrolysis and Hydrogenolysis

AbstractThe novel two–dimensional MXene material Ti3C2Tx has the advantages of a large specific surface area, adjustable band gap, good electrical conductivity, and high stability. However, the precipitation of hydrogen via electrolytic water splitting over Ti3C2Tx has unacceptably slow kinetics. In this paper, Co nanoparticles were incorporated on the Ti3C2TxMXene surface via electrostatic adsorption by utilizing the intrinsic MXene defects generated during the etching process. Next, a Fe−Co alloy structure was also constructed on the Ti3C2TxMXenesurface by wet chemical impregnation method using the principle of galvanic coupling substitution. The prepared catalyst had an overpotential of 118 mV at a current density of 10 mA‐cm−2 and a Tafel slope of 97.56 mV dec−1. The Fe−Co alloy structure accelerated the kinetic hydrogen precipitation step, and Fe−Co/Ti3C2Txshowed excellent stability when used in a water electrolysis process for 11 h. This work offers a promising strategy for the synthesis of intrinsically defective synthetic alloy MXene structures.

Effects of ion-plasma treatment temperature of the aluminium coating on the structure and phase composition of the VT6 titanium alloy

In this study, we studied the effects of aluminum coating treatment temperature on the microstructure and phase composition when applied to a VT6 titanium alloy substrate within a low-pressure arc discharge plasma environment. The ion-plasma treatment was conducted at 450 and 500 °C, employing argon shielding, while the aluminum coating was deposited using the vacuum-arc process, resulting in a coating thickness of ~3 μm. Microstructural analysis was performed using a scanning electron microscope, and the structural and phase composition were examined using X-ray diffraction (XRD) imaging in symmetric imaging mode with CuKα radiation. Our findings demonstrate that the application of the aluminum coating initiates the formation of a near-surface α-stabilized layer, extending up to 2.5 μm in thickness due to the heat generated during the ion cleaning process. Subsequent ion-plasma treatment further results in the development of a TiAl3 intermetallide site, reaching thicknesses of up to 1.5 μm, while the α-stabilized region expands to 5.5 μm. Higher temperatures during the treatment process contribute to an increase in the thickness of these aforementioned layers and also lead to the emergence of an intermediate TiAl intermetallic layer.

Impact of Catalysis-Relevant Oxidation and Annealing Treatments on Nanostructured GaRh Alloys.

In this study, we examine the surface-derived electronic and chemical structures of nanostructured GaRh alloys as a model system for supported catalytically active liquid metal solutions (SCALMS), a novel catalyst candidate for dehydrogenation reactions that are important for the petrochemical and hydrogen energy industry. It is reported that under ambient conditions, SCALMS tends to form a gallium oxide shell, which can be removed by an activation treatment at elevated temperatures and hydrogen flow to enhance the catalytic reactivity. We prepared a 7 at. % Rh containing the GaRh sample and interrogated the evolution of the surface chemical and electronic structure by photoelectron spectroscopy (complemented by scanning electron microscopy) upon performing surface oxidation and (activation treatment mimicking) annealing treatments in ultrahigh vacuum conditions. The initially pronounced Rh 4d and Fermi level-derived states in the valence band spectra disappear upon oxidation (due to formation of a GaOx shell) but reemerge upon annealing, especially for temperatures of 600 °C and above, i.e., when the GaOx shell is efficiently being removed and the Ga matrix is expected to be liquid. At the same temperature, new spectroscopic features at both the high and low binding energy sides of the Rh 3d5/2 spectra are observed, which we attribute to new GaRh species with depleted and enriched Rh contents, respectively. A liquefied and GaOx-free surface is also expected for GaRh SCALMS at reaction conditions, and thus the revealed high-temperature properties of the GaRh alloy provide insights about respective catalysts at work.

Improving the performance of machine learning model predicting phase and crystal structure of high entropy alloys by the synthetic minority oversampling technique

It is critical to select the suitable integration of elements that has an influence on phase formation when selecting the proper High Entropy Alloys (HEAs) with desired qualities. Machine Learning (ML) models were used to predict the phase and crystal structure of HEAs in this study. Trained on extensive experimental datasets, the set of input characteristics includes Atomic size difference, Mixing Enthalpy, Mixing Entropy, Valence Electron concentration, Electronegativity difference, Ω and Average Melting Temperature. The phase is divided into three categories: Solid solution (S), Dual phase (D), and Intermetallic (Im). Crystal structure classifications include BCC, FCC, and FCC+BCC. For phase and crystal structure prediction, five ML algorithms were used: Decision Tree (DT), K Nearest Neighbour (KNN), Random Forest (RF), Gradient Boosting (GB) and eXtreme Gradient Boosting (XG Boosting), The classification of the HEAs phase has been predicted with great accuracy using an XG Boosting (80 %) and Random Forest exhibits the highest accuracy (94 %) for crystal structure prediction when model is trained on an experimental dataset. Even though the ML model predicts the classes with a better degree of accuracy (>80 %), the F1 value of each class varies more dramatically. This issue has arisen as a result of an imbalance in the dataset's class distribution. To boost performance, this work uses an ML model in conjunction with the Synthetic Minority Oversampling Technique (SMOTE). According to this approach, XG boosting identified the crystal structure with 93 % accuracy and predicted the phase of HEAs with 84 % accuracy. Additionally, it has been noted that each class's F1 score improved and the difference between them was reduced after using the SMOTE technique. It is evident that the SMOTE approach has improved the ML model's ability to differentiate between the various classes.

Experimental study on mechanical behaviour of friction stir welded aluminium alloy butt joints

The purpose of this paper is to understand the softening extent and stress-strain behavior of the normal-strength 6061-T6, 6013-T6, and high-strength 7075-T6 aluminium alloy butt joints using the novel friction stir welding (FSW) technique. A total of 107 monotonic tensile coupons and 33 Vickers hardness coupons were prepared from 8- or 12-mm thick welded plates using various tool rotation speed, welding transverse speed and tool configurations. The surface morphology, stress-strain curves and hardness distribution laws after welding were evaluated. The W-shaped hardness profiles were clearly observed, with the fracture location positively correlated at the lowest point of Vickers hardness near the edge of the weld toe. The strength reduction and softening extent of extruded aluminium alloys in T6 temper induced by FSW were superior to those of aluminium alloys using fusing welding process outlined in the Chinese and European standards, indicating the effectiveness and applicability of the FSW technique in the formation of components and connections for aluminium alloy structures. Additionally, the current widely used constitutive models generally yielded under-estimations on the strength under large strains. The developed three-stage Ramberg-Osgood model, using seven key input parameters, significantly improved the accuracy and consistent predictions in the full-range stress-strain curve of FSW aluminium alloys. Furthermore, the suggested model could still achieve a great balance between accuracy and practicality when using just three common available parameters with the employment of predictive expressions on other four parameters.

Synergistic Ni-W Dimer Sites Induced Stable Compressive Strain for Boosting the Performance of Pt as Electrocatalyst for the Oxygen Reduction Reaction.

Alloying Pt catalysts with transition metal elements is an effective pathway to enhance the performance of oxygen reduction reaction (ORR), but often accompanied with severe metal dissolution issue, resulting in poor stability of alloy catalysts. Here, instead of forming traditional alloy structure, we modify Pt surface with a novel Ni-W dimer structure by the atomic layer deposition (ALD) technique. The obtained NiW@PtC catalyst exhibits superior ORR performance both in liquid half-cell and practical fuel cell compared with initial Pt/C. It is discovered that strong synergistic Ni-W dimer structure arising from short atomic distance induced a stable compressive strain on the Pt surface, thus boosting Pt catalytic performance. This surface modification by synergistic dimer sites offers an effective strategy in tailoring Pt with excellent activity and stability, which provides a significant perspective in boosting the performance of commercial Pt catalyst modified with polymetallic atom sites.

Synergistic Ni−W Dimer Sites Induced Stable Compressive Strain for Boosting the Performance of Pt as Electrocatalyst for the Oxygen Reduction Reaction

AbstractAlloying Pt catalysts with transition metal elements is an effective pathway to enhance the performance of oxygen reduction reaction (ORR), but often accompanied with severe metal dissolution issue, resulting in poor stability of alloy catalysts. Here, instead of forming traditional alloy structure, we modify Pt surface with a novel Ni−W dimer structure by the atomic layer deposition (ALD) technique. The obtained NiW@PtC catalyst exhibits superior ORR performance both in liquid half‐cell and practical fuel cell compared with initial Pt/C. It is discovered that strong synergistic Ni−W dimer structure arising from short atomic distance induced a stable compressive strain on the Pt surface, thus boosting Pt catalytic performance. This surface modification by synergistic dimer sites offers an effective strategy in tailoring Pt with excellent activity and stability, which provides a significant perspective in boosting the performance of commercial Pt catalyst modified with polymetallic atom sites.

Development of instruments for imaging of local magnetic structure by magnetic neutron holography

We have developed instruments for magnetic neutron holography (MNH) using polarized white neutrons to investigate the local magnetic structures of magnetic alloys. We chose the 3He spin filter method as the neutron polarizer to polarize neutrons over a wide wavelength range of up to a few 100 meV. We developed a magnet device to saturate the magnetizations of ferromagnetic samples, and instruments to transport polarized neutrons from a 3He spin filter to the MNH sample. The neutron polarization, Pn, at the beginning of the MNH experiments was confirmed to be 0.46, which is feasible for MNH. Using the developed instruments, we obtained preliminary results for the room-temperature ferromagnetic alloy Fe0.08Co0.92. Technical problems encountered in the experiments and ways to overcome them are discussed. Based on these results, we believe that MNH that use polarized neutrons is promising.

Recent advances in synchrotron X-ray studies of the atomic structures of metal alloys in liquid state

Research into the atomic structures of metal materials in the liquid state, their dynamic evolution versus temperature until the onset of crystal nucleation has been a central research topic in condensed matter physics and materials science for well over a century. However, research and basic understanding of the atomic structures of liquid metals are far less than those in the solid state of the same compositions. This review serves as a condensed collection of the most important research literature published so far in this field, providing a critical and focused review of the historical research development and progress in this field since the 1920s. In particular, the development of powerful synchrotron X-ray sources and the associated experimental techniques and sample environments for studying in-situ the atomic structures of different metallic systems. The key findings made in numerous pure metals and metallic alloy systems are critically reviewed and discussed with the focus on the results and new understandings of structural heterogeneities found inside a bulk liquid, at the liquid surface or liquid-solid interface. The possible future directions of research and development on the most advanced experimental and modeling techniques are envisaged and briefly discussed as well.

Effect of Y element on atomic structure, glass forming ability, and magnetic properties of FeBC alloy

Abstract The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe86−x Y x B7C7 (x = 0, 5, 10 at.%) amorphous alloys via both experiments and ab initio molecular dynamics simulations. Furthermore, we explore the correlation between local atomic structures and properties. Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters, which can potentially enhance both glass-forming ability and thermal stability. These findings have been experimentally validated. The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals, resulting in a reduction in ferromagnetic coupling between Fe atoms. This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system, which is consistent with experimental results. The results could help understand the relationship between atomic structure and magnetic property, and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.

Magnesium ions enhanced core-shell lattice matching for Narrow-Band green emission indium phosphide QDs

Indium phosphide QDs have emerged as a promising candidate for the next generation optoelectronic applications. However, the optical performance of InP QDs still lags behind that of CdSe-based QDs, partly due to surface traps induced by the lattice mismatch between InP and ZnSe. Herein, based on (DMA)3P, we designed an alloyed inner-shell structure of InP/Zn(Mg)Se/ZnS QDs. The dual-function mechanism of the Zn(Mg)Se was revealed, which effectively mitigates the lattice mismatch between the core and shell toreduce the emission of surface defect states, resulting in narrowed emission peaks (FWHM ∼ 36 nm). While the increased band gap of Zn(Mg)Se confines the exciton delocalization from core to shell, thereby reducing the non-radiative relaxation of carriers at the defect states in the shell. This discovery provides a strategy to improve the color purity and luminescence efficiency of InP QDs. By combining blue LED chips with InP/Zn(Mg)Se/ZnS, a white light-emitting diode (QLED) with a high luminous efficiency of 63 lm/W was obtained. Furthermore, the realization of QDs arrays with 10 μm pixel dots by inkjet printing technology and the fabrication of white-light emitting Micro-LEDs by combining QDs films with Micro-LED chip arrays demonstrate the potential application of InP QDs in high-efficiency optoelectronic devices (LEDs/micro-LEDs).

Effects of tempering treatment on structural evolution and electrochemical properties of laser cladded NiAlCrZrMo medium–entropy alloy coating by DFT calculation

A NiAlCrZrMo medium–entropy alloy (MEA) coating with solid solution was fabricated by laser cladding, which was evolved to high–entropy alloy (HEA) structure by tempering treatment for the improvement of corrosion resistance. The effects of tempering treatment on the structural evolution and electrochemical properties of obtained MEA coatings were comparatively investigated, and the corrosion mechanism was discussed with the density functional theory (DFT) calculation. The results show that the MEA structure of original MEA coating is evolved to HEA structure of tempered MEA coating by tempering treatment, which is composed of AlNi2Ti and Cr phases. The charge transfer resistance of tempered MEA coating is increased by ∼140 times compared with the original MEA coating, in which the diffusion of electrons is held back by its HEA structure. Moreover, the tempered MEA coating possesses higher electrochemical resistance compared with the original MEA coating, which is attributed to the AlNi2Ti phase of tempered MEA coating decreasing the corrosion tendency by the effect of high–entropy evolution.

Process optimization–oriented deformation control of large aluminum alloy structures from high-speed EMU

Process optimization–oriented deformation control of large aluminum alloy structures from high-speed EMU

Experimental and theoretical study on high-temperature creep of VT6 titanium alloy under multi-axial loading conditions

In the framework of damage mechanics, we discuss a new mathematical model that describes the kinetics of the stress–strain state and damage accumulation during material degradation by the mechanism of long-term strength under complex multiaxial stress state. An experimental and theoretical technique is proposed for determination of material parameters and scalar constitutive functions for damaged media based on specially set experiments on laboratory specimens. The results of experimental studies and numerical simulations of short-term high-temperature creep of VT6 titanium alloy under uniaxial and multiaxial loading are presented. Numerical results are compared with the data obtained through experiments. Particular attention is paid to simulating the process of unsteady creep for complex deformation modes, accompanied by rotation of main areas of stress, strain and creep strain tensors. It is shown that the developed version of the constitutive relations of the damaged media enables us to describe the processes of unsteady creep and long-term strength of structural alloys under multiaxial stress with the accuracy sufficient for engineering calculations.

Endowing low fatigue for elastocaloric effect by refined hierarchical microcomposite in additive manufactured NiTiCuCo alloy

NiTiCu-based shape memory alloys have been considered as ideal materials for solid-state refrigeration due to their superb cycling stability for elastocaloric effect. However, the embrittlement and deterioration caused by secondary phase and coarse grains restrict their applications, and it is still challenging since the geometric components are required. Here, bulk NiTiCuCo parts with excellent forming quality were fabricated by laser powder bed fusion (LPBF) technique. The as-fabricated alloy exhibits refined three-phases hierarchical microcomposite formed based on the rapid cooling mode of LPBF, composed of intricate dendritic Ti2Ni–NiTi composite and nano Ti2Cu embedded inside the NiTi-matrix. This configuration endows far superior elastocaloric stability compared to the as-cast counterpart. The low fatigue stems from the strong elastic coupling between the interphases with reversible martensite transformation, revealed by in-situ synchrotron high-energy x-ray diffraction. The fabrication of NiTiCuCo alloy via LPBF fills the bill of complex geometric structures for elastocaloric NiTiCu alloys. The understanding of interphase micro-coupling could provide the guide for designing LPBF fabricated shape memory-based composites, enabling their applications for special demands on other functionalities.

Microstructure and Mechanical Properties Ultrasonic Assistance Laser Welded Joints of Beta Titanium Alloy with Multiple Vibrators

Aiming at the problem of deterioration of the properties of beta titanium alloy welded joints due to many porosity defects and coarse grains, multi-vibrator ultrasonic-assisted laser welding (M—ULW) technology was used to improve the structure and properties of beta titanium alloy welded joints. The microstructure evolution, tensile strength, elongation, and fracture behavior of the weld joint were studied through scanning electron microscopy, electron back-scatter diffraction, and a universal testing machine. The results show that ultrasonic vibration has no effect on the phase composition of titanium alloy welds during ultrasonic-assisted laser welding. However, it caused all grains in the weld to be transformed into equiaxed grains, and the higher the amplitude, the finer and more uniformly distributed were the equiaxed grains. When the ultrasonic amplitude reached 20 μm, the fine equiaxed crystals were uniformly distributed throughout the weld, and the average grain size of the weld was 56.15 um, which is only one-third of that of the unultrasonicated laser welded joint. Ultrasonic refinement makes the joint grain size decrease, weakens the beta titanium alloy {200} direction weaving, increases the dislocation density within the weld; and increases the tensile strength of the welded joint. The tensile strength of the welded joints exceeded that of the base material by 907 MPa, and the elongation was significantly increased by a factor of 1.8 compared with that of the un-ultrasonicated laser welded joints, resulting in a shift of the fracture location from the center of the weld to the heat-affected zone.

Constructing interlaced network structure by grain boundary corrosion methods on CrCoNiFe alloy for high-performance oxygen evolution reaction and urea oxidation reaction

Corrosion engineering is an effective way to improve the oxygen evolution reaction (OER) activity of alloys. However, the impact of grain boundary corrosion on the structure and electrochemical performance of alloy is still unknown. Herein, the vacuum arc-melted CrCoNiFe alloys with interlaced network structures via grain boundary corrosion methods were fabricated. The grain boundaries that existed as defects were severely corroded and an interlaced network structure was formed, promoting the exposure of the active site and the release of gas bubbles. Besides, the (oxy)hydroxides layer (25 nm) on the surface could act as the true active center and improve the surface wettability. Benefiting from the unique structure and constructed surface, the CrCoNiFe-12 affords a high urea oxidation reaction (UOR) performance with the lowest overpotential of 250 mV at 10 mA/cm2 in 1 M KOH adding 0.33 M urea. The CrCoNiFe-12||Pt only required a cell voltage of 1.485 V to afford 10 mA/cm2 for UOR and long-term stability of 100 h at 10 mA/cm2 (27.6 mV decrease). These findings offer a facile strategy for designing bulk multiple-principal-element alloy electrodes for energy conversion.

The Effect of Heat Treatment and Tungsten Content on the Structure, Phase Composition, and Corrosion Resistance of High-Entropy Alloys of the Fe–Cr–Ni–Mo–W System

The Effect of Heat Treatment and Tungsten Content on the Structure, Phase Composition, and Corrosion Resistance of High-Entropy Alloys of the Fe–Cr–Ni–Mo–W System

Structure of Al82Cu7Fe11 Alloy After High-Speed Quenching

Structure of Al82Cu7Fe11 Alloy After High-Speed Quenching