Lattice Parameters Of Alloys Research Articles

Effect of phase composition and cluster structure on de-/hydriding kinetics of as-cast and heat-treated Ti33V37Mn30-xCrx alloys

To enhance the hydrogen storage property, elements Mn in Ti33V37Mn30 alloy were partially substituted with varying concentrations of elements Cr. The Ti33V37Mn24Cr6 variant, which exhibited superior performance, was selected for further analysis. Ti33V37Mn24Cr6 samples were first heat-treated separately at 773K, 973K and 1173K for 2h, and then water-quenched. The effect of Cr substitution and heat treatment on the microstructure and de-/hydriding properties of Ti33V37Mn30-xCrx alloys were investigated. As-cast alloys were composed of BCC phases mainly, along with some C14 Laves phases and Ti-rich phases. The lattice parameter of BCC phases in Ti33V37Mn24Cr6 increased to 3.053 Å. Cr substitution changed the tetrahedral gap of the alloy. At 298K, the initial hydrogen absorption capacity and the maximum hydrogen desorption capacity of Ti33V37Mn24Cr6 were raised to 3.07 wt% and 1.81 wt%, respectively. The lattice parameter of Ti33V37Mn24Cr6 alloys heat-treated at 773K also enlarged to 3.056 Å. Elevating the heat treatment temperature to 973K and 1173K significantly raised the proportion of C14 Laves phases in the alloy. Hydrogen storage performance of heat-treated alloys was examined at 298K. The results suggested that the heat-treated alloys could be fully activated after one hydrogen ab-/desorption cycle. Ti33V37Mn24Cr6 alloy heat-treated at 773K achieved the maximum hydrogen desorption capacity of 1.83 wt%, with an accelerated hydrogen ab-/desorption rate.

Accelerating Elastic Property Prediction in Fe-C Alloys through Coupling of Molecular Dynamics and Machine Learning.

The scarcity of high-quality data presents a major challenge to the prediction of material properties using machine learning (ML) models. Obtaining material property data from experiments is economically cost-prohibitive, if not impossible. In this work, we address this challenge by generating an extensive material property dataset comprising thousands of data points pertaining to the elastic properties of Fe-C alloys. The data were generated using molecular dynamic (MD) calculations utilizing reference-free Modified embedded atom method (RF-MEAM) interatomic potential. This potential was developed by fitting atomic structure-dependent energies, forces, and stress tensors evaluated at ground state and finite temperatures using ab-initio. Various ML algorithms were subsequently trained and deployed to predict elastic properties. In addition to individual algorithms, super learner (SL), an ensemble ML technique, was incorporated to refine predictions further. The input parameters comprised the alloy's composition, crystal structure, interstitial sites, lattice parameters, and temperature. The target properties were the bulk modulus and shear modulus. Two distinct prediction approaches were undertaken: employing individual models for each property prediction and simultaneously predicting both properties using a single integrated model, enabling a comparative analysis. The efficiency of these models was assessed through rigorous evaluation using a range of accuracy metrics. This work showcases the synergistic power of MD simulations and ML techniques for accelerating the prediction of elastic properties in alloys.

Effects of second metals (M = Fe, Cu, Ga, In, Sn) on the geometric and electronic properties of platinum for the direct dehydrogenation of propane

Supported Pt-based bimetallic catalysts are representative types of dehydrogenation catalysts used for alkanes to olefins conversion. The platinum in these catalysts exhibits unique structural features accompanied with changes in electronic states due to the addition of the second metal. To investigate the impact of each effect on the activity for propane dehydrogenation, a series of Pt-M/SiO 2 (M= Fe, Cu, Ga, In and Sn) catalysts were prepared and used for propane dehydrogenation. Utilizing various characterization techniques, the geometric and electronic properties of these catalysts were studied. The relationships between the specific activity of bimetallic platinum catalysts in propane dehydrogenation and atomic sizes of alloys (i) and the total density of unoccupied d bands in platinum (ii) were considered. Via alloy formation, it was found that dilution of the active metal Pt occurred in these SiO 2 supported bimetallic catalysts, and the lattice parameter of Pt-M alloys decreased on Pt-Fe, Pt-Cu and Pt-Ga alloys, but increased on Pt-In and Pt-Sn alloys when compared with that of Pt foil. Catalytic activity was evidently shown to not be a function of the lattice parameters of Pt-M alloys, but appears closely related with the d -holes of Pt in Pt-M bimetallic catalysts. More d holes show favorably high activity. Among the studied Pt-M/SiO 2 (M= Fe, Cu, Ga, In and Sn) catalysts, the prominent and primary role of the electronic effect was demonstrated. • Mansour’method was used to quantitatively determine the electronic state of Pt. • Pt-Ga/SiO 2 catalyst exhibits biggest d -holes and highest initial conversion of propane. • The electronic effect plays a crucial role in studied systems.

Microstructure and Mechanical Properties of Co32Cr28Ni32.94Al4.06Ti3 High-Entropy Alloy.

High-entropy alloys have good application prospects in nuclear power plants due to their excellent mechanical properties and radiation resistance. In this paper, the microstructure of the Co32Cr28Ni32.94Al4.06Ti3 high-entropy alloy was researched using metallurgical microscopy, X-ray diffraction, and scanning electron microscopy. The mechanical properties were tested using a Vickers microhardness tester and a tensile testing machine, respectively. The results showed that Co32Cr28Ni32.94Al4.06Ti3 had a single-phase, disordered, face-centered, cubic solid-solution structure and was strengthened by solid solution. The alloy lattice parameter and density were estimated as 0.304 nm and 7.89 g/cm3, respectively. The test results indicated that the alloy had satisfactory mechanical properties with yield stress and tensile strength of about 530 MPa and 985 MPa, respectively.

Mechanical properties and yield strength modeling of a medium entropy alloy containing L12 precipitates

Medium/High Entropy Alloys (M/HEAs) exit over immense compositional fields, which represent a challenging opportunity for the development of alloys with optimized properties. To realize their potential, we need to be able to predict properties of interest from different compositions effectively. Precipitation strengthened alloys are of wide interest, but their yield strength modeling is not simple because many factors as precipitate type, size, fraction, and composition play important roles. The Cr29.7Co29.7 Ni35.4Al4.0Ti1.2 (at%) alloy was designed to have a highly concentrated Cr-Co-Ni face centered cubic matrix with L12 precipitates. In the present work, this alloy was aged at 850 °C for times up to 166 h and had its yield strength measured in the different aging conditions through tensile tests. A recently developed model to calculate the solid solution contribution in FCC multi-principal element alloys was coupled with classical grain-boundary strengthening and precipitation hardening models to predict the yield strength of the studied alloy. We show that the different strengthening contributions can be modeled independently with satisfactory accuracy. The results can be easily extrapolated to other alloys of the Cr-Co-Ni-Al-Ti system. An empirical relationship to estimate the room temperature lattice parameter of FCC alloys is also proposed. A promising route to explore the vast compositional space of M/HEA and design new precipitation hardening alloys with optimized mechanical properties is suggested.

Effect of electron localization in theoretical design of Ni-Mn-Ga based magnetic shape memory alloys

The precise determination of the stability of different martensitic phases is an essential task in the successful design of (magnetic) shape memory alloys. We evaluate the effect of electron delocalization correction on the predictive power of density functional theory for Ni-Mn-Ga, the prototype magnetic shape memory compound. Using the corrected Hubbard-model-based generalized gradient approximation (GGA+U), we varied the Coulomb repulsion parameter U from 0 eV to 3 eV to reveal the evolution of predicted material parameters. The increasing localization on Mn sites results in the increasing stabilization of 10M modulated structure in stoichiometric Ni2MnGa in agreement with experiment whereas uncorrected GGA and meta-GGA functional provide the lowest energy for 4O modulated structure and non-modulated structure, respectively. GGA+U calculations indicate that 10M structure is more stable than other martensitic structures for U > 1.2 eV.The key features of density of states (DOS) responsible for the stabilization or destabilization of particular martensitic phases calculated with GGA+U are found also in DOS calculated with advanced quasi-particle self-consistent GW (QSGW) method. It supports the physical background of Hubbard correction. Moreover, the calculations with U = 1.8 eV provide the best agreement with experimental data for lattice parameters of stoichiometric and off-stoichiometric alloys.

Fabrication and characterization of nano-Cr2O3 dispersed mechanically alloyed and conventional sintered W-Zr alloys

Tungsten based alloys with stoichiometric composition of W98.5Zr0.5(Cr2O3)1 (alloy A), W97.5Zr00.5(Cr2O3)2 (alloy B) and W98Zr1(Cr2O3)1 (alloy C) (all in weight %) were synthesized through mechanical alloying (MA) for 20 h followed by conventional sintering at 1500 °C for 2 h in argon atmosphere. The milled powders and consolidated alloys has been investigated using X-ray diffraction (XRD), Particle size analyzer, Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Elemental mapping (EM). Minimum crystallite size of 11.81 nm and maximum lattice strain and dislocation density of 0.44% and 47.98 × 1016/m2 respectively were observed in alloy A at 20 h milling. Lattice parameter of alloys A through C increases upto 5 h further decreases past 5 h of milling. Excellent powder flowability was found in alloy A with minimum angle of repose (°) α = 25.029° at 20 h mechanically milled powder. Higher dispersion stability noticed in alloy C with zeta potential value −15.5 mV among all 20 h milled powder in pH2.4. The minimum average particle size of 321.6 nm was found in alloy C at 20 h milled powder on dilution with water has been measured using Dynamic light scattering (DLS). ZrCr2 intermetallics in the sintered alloys evident of both solid phase and liquid phase sintering. Maximum Sinterability and hardness of 91.46% and 13.613 GPa respectively observed in alloy A due to its fine crystallite size.

The effect of stress on surface and interface segregation in thin alloy films on inert substrates

We employed a regular solution-type model to describe the equilibrium segregation of solute atoms on the external surface and at the film–substrate interface in the ultrathin single-crystalline films of binary metal alloys attached to an inert substrate. The finite size of the system, the interlayer interactions in the film and the heteroepitaxial strain in the film were taken into account. We demonstrated that the homogeneous heteroeptiaxial strain in the film affects the surface and interface segregation of solute atoms only in the case when the value of coherency strain parameter (describing the relative change of alloy lattice parameter upon addition of solutes) in the surface and interface layers is different from its value in the rest of the films. The developed model was applied to the Ni(Au) thin films deposited on sapphire substrate. The quantitative agreement between the model predictions and recent experimental data on interface segregation of Au could be achieved by assuming that the film is heteroepitaxially compressed.

Structural, electronic and magnetic properties of MxPt1-X, (M= Co, Ni and V) binary alloys

The structural, optical and magnetic properties of ordered MxPt1-x (M = Co, Ni and V) binary alloys have been investigated using Vienna ab initio Simulation Package (VASP) within the framework of Density Functional Theory (DFT) and the Generalized Gradient Approximation (GGA). Ab initio calculations have been performed to obtain the most stable structure for each of the three binary systems. In addition, the optical and electrical properties such as electronic band structure, density of states and partial density of states of MxPt1-x binary alloys have been investigated. Specifically, total energy minimization has been performed to calculate the equilibrium in-plane, ao, out-of-plane, co, and volume, Vo, structural lattice parameters of MxPt1-x binary alloys. We found that ao, co and Vo for CoPt, NiPt and VPt3 equal to (ao = 3.806 A, co = 3.707 A and Vo = 53.7 A3) (ao = 3.84 A, co = 3.62 A and Vo = 53.64 A3) and (ao = 3.88 A, co = 7.88 A and Vo = 118.71 A3) respectively. Furthermore, the magneto-crystalline anisotropy energies (MAE) have been calculated to get a deeper insight into magnetic characteristics of the MxPt1- x binary alloys. We found that MAE values for CoPt, NiPt and VPt3 binaries are equal to 1.60, 0.231 and 0.0116 meV/unit cell respectively. These MAE values correspond to magneto-crystalline anisotropy constant K values equal to 4.8 ×107, 6.9 ×106 and 1.46 × 105 erg/cm3. The obtained results reveal that CoPt and NiPt binary systems exhibit attractive optical and magnetic properties, which make both systems potential candidates for magneto-optical and optical-electronic devices. Our results are in good agreement with the previous experimental and theoretical findings.

Strain and Band-Gap Engineering in Ge - Sn Alloys via P Doping

Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge-Sn alloys. The heavily doped n-type Ge-Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge-Sn layers and to modify the lattice parameter of P-doped Ge-Sn alloys. The strain engineering in heavily-P-doped Ge-Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge-Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1x10^20 cm-3 the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology.

Investigation of the Li solubility in the intermediate phase Li17Sn4 relevant to understanding lithiation mechanisms in Sn-based anode materials

A comprehensive study of the Li-rich phase boundary of the intermediate Li17Sn4 compound is given based on thermochemical and electrochemical investigations. From the results a partial phase diagram showing the homogeneity range of this phase could be constructed. Using these results, the defect mechanism for the compound Li17Sn4 could also be clarified. Galvanostatic coulometry with potential limitation (GCPL) was performed using 2032 coin cell equipment. This allowed for the determination of the amount of Li insertion on special crystallographic sites at 25 °C, which is 0.41 ± 0.04 at.%. The respective Li loss mechanisms (solid electrolyte interface formation, Li plating, Li trapping) are discussed. Irreversible capacity according to Li trapping could be excluded due to the limited voltage window of the experiments. Moreover, differential scanning calorimetry (DSC) was carried out on two individual Tian-Calvet type calorimeters. The Li-rich boundary of the Li17Sn4 compound was determined at 81.31 ± 0.04 (C-80) and 81.28 ± 0.05 at.% Li (M-HTC) at 427 °C. In addition, the latter results were compared to the change of lattice parameters of alloys with compositions Li17+xSn4.

Structural and elastic properties of zinc-blende and wurtzite InN1-Bi alloys

Structural and elastic properties of InN1-xBix alloys in both zinc-blende and wurtzite phases are studied by using first-principle calculations. Two different Bi-atom arrangements of uniform and clustered configurations have been considered for x = 0.25, 0.5, and 0.75. It is found that clustered configuration has a significant effect on lattice parameters of wurtzite InN1-xBix alloys. A slightly sublinear dependence on the alloy content, x, can be accepted for C11, C12, C13, and C33 in zinc-blende InN1-xBix, and for C12, C13, and C44 in wurtzite InN1-xBix, whereas clearly linear deviations are obtained for C44 and C66 in zinc-blende alloys and for C11 and C33 in wurtzite alloys. The effect of Bi atoms clustering leads to a decrease in all elastic constants and bulk modulus in zinc-blende InN1-xBix, and makes big deviations from Vegard's-like law and has little influence on bulk modulus in wurtzite InN1-xBix alloys.

First-principles modeling of energetic and mechanical properties of Ni–Cr, Ni–Re and Cr–Re random alloys

We apply the exact-muffin-tin-orbitals (EMTO) method to investigate structural properties, formation enthalpies, mechanical stability and polycrystalline moduli in Ni–Re, Ni–Cr and Cr–Re disordered fcc, bcc and hcp phases. Substitutional disorder is treated by using the coherent potential approximation (CPA). We predict the alloy lattice parameters in good agreement with the experiment. We find a continuous softening, as a function of Cr composition, of the tetragonal shear modulus C′ in fcc Ni–Cr phase indicating mechanical instability in Cr-rich Ni–Cr alloys. On the other hand, we show that the mechanical stability of fcc Ni–Re alloys persists through the whole composition range. We observe an intriguing behaviour of the Young’s modulus vs. the intrinsic ductility curve in Ni-rich Ni–Re fcc phase.

First-Principles Calculations of Electronic and Magnetic Properties in Ferromagnetic MnSeS, MnSeTe, and MnSePo Ternary Systems

In this paper, we present theoretical investigations of electronic and magnetic properties of the ordered cubic ferromagnetic MnSexS1 −x, MnSexTe1 −x, and MnSexPo1 −x for x = 0.25, 0.50, and 0.75 using the full-potential linearized augmented plane wave method. Regarding structural properties, we found that the lattice parameters of MnSeS, MnSeTe, and MnSePo alloys follow Vegard’s law. Results show that MnSexTe1 −x exhibits a half-metallic behaviour for all Mn concentrations, while MnSeS is half-metallic only for x = 0.5 and 0.75, and MnSePo is half-metallic only for x = 0.25. Moreover, a total magnetic moment of 5 µB is found for all alloys where the half-metallic phase is present. The total magnetic moment is found to be independent of composition and it is mainly due to the Mn atom.

X-ray studies of dynamic aging in an aluminum alloy subjected to severe plastic deformation

In this work, X-ray scattering methods were applied for a quantitative characterization of the microstructure of an aluminum alloy of the Al–Mg–Si system during dynamic aging realized through the high pressure torsion technique. A qualitative and quantitative phase analysis of the alloy was performed, together with Al alloy lattice parameter determination. From the reflections broadening the effective size of the coherent scattering domains and the lattice microstrain were determined in the framework of the Halder–Wagner approach. Using the method of small-angle X-ray scattering, the quantitative characteristics of the size, shape and spatial distribution of the secondary phase particles formed in the Al alloy during dynamic aging were established. In order to validate the obtained results, the method of small-angle X-ray scattering was preliminarily tested on similar samples after artificial aging and compared with the results from small-angle neutron diffraction widely known in literature.

Effects and mechanism of Ti, Ni, Sc, Fe substitution on the thermal stability of zirconium cobalt–hydrogen system

ZrCo alloys with Ti, Sc, Ni, Fe substitution (Zr0.8Ti0.2Co, Zr0.8Sc0.2Co, ZrCo0.8Ni0.2, ZrCo0.8Fe0.2) were prepared via arc-melting method, and then products before and after hydrogenation were characterized by X-ray diffraction. Results showed that the crystal structure of ZrCo alloys substituted with Ti, Sc, Ni and Fe substitution formed cubic phase, and the lattice parameters of ZrCo alloys and these hydrides decreased with Ti substituted, while increased with Sc, Ni, Fe substitution. The dehydrogenation pressure composition isotherms for all these alloys were obtained in the temperature range between 523 K and 623 K, and it was found that desorption plateau pressure increased in order of ZrCo0.8Fe0.2 < ZrCo < Zr0.8Sc0.2C < ZrCo0.8Ni0.2 < Zr0.8Ti0.2Co. Meanwhile, the enthalpy and entropy change for hydrogen desorption were calculated. And the kinetics of hydrogen-induced disproportionation in desorption mode for all these alloys was also investigated. Results demonstrated that the rate and extent of disproportionation of ZrCo alloys decreased with Ti substitution, while increased with Sc, Ni and Fe substitution. Thermal analytical method (DSC) was carried out to investigate the mechanism of thermal stability change of ZrCo alloys after Ti, Sc, Ni, Fe substitution. It could be inferred that the effect of element substitution on disproportionation of ZrCo alloys was caused by the radius change of hole sizes of hydrogen occupation sites.

Bulk lattice parameter and band gap of cubic InXGa1−XN (001) alloys on MgO (100) substrates

InxGa1−xN (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted molecular beam epitaxy system. We determined the in-plane [001] and in-growth [110] lattice parameters, as well as the bulk lattice parameter of the alloys for different In concentrations by high resolution X-ray diffraction. The In concentration was determined assuming Vegard׳s law for the alloy lattice parameter. The optical energy gap of InxGa1−xN has been determined by transmittance measurements from absorption edges for several In concentrations. Our results show that the alloys have a direct band gap for all In concentrations and a bowing parameter b=1.84.

A concurrent multi-scale technique in modeling heterogeneous FCC nano-crystalline structures

In this paper, a multi-scale molecular dynamics–finite element coupling is presented to study the mechanical behavior of heterogeneous nano-crystalline structures. The stiffness and mass matrices of the continuum sub-domain are generated by applying a linear transformation on the matrices obtained via the atomic structure underlying the FE mesh. A Lagrange multiplier method is employed to the transition zone imposing velocity resemblance of the coupling regions. The constraint equations of motion are solved by the multi-time-step decomposition thus giving the opportunity to ascribe different time steps to each individual zone. The molecular dynamics is performed by employing the Sutton–RafiiTabar many body potential (Raffi-Tabar and Sutton, 1991) for FCC metallic alloys, and its integrity is attained by calculating the effective lattice parameter of different random alloys by minimizing the general form of Sutton–RafiiTabar interatomic potential energy. The authenticity and accuracy of the renovated concurrent scheme is remarkably acquired by comparing some numerical results of the proposed multi-scale model to those of implemented and validated molecular dynamics.

Alloying-related trends from first principles: An application to the Ti–Al–X–N system

Tailoring and improving material properties by alloying is a long-known and used concept. Recent research has demonstrated the potential of ab initio calculations in understanding the material properties at the nanoscale. Here, we present a systematic overview of alloying trends when early transition metals (Y, Zr, Nb, Hf, and Ta) are added in the Ti1−xAlxN system, routinely used as a protective hard coating. The alloy lattice parameters tend to be larger than the corresponding linearised Vegard's estimation, with the largest deviation more than 2.5% obtained for Y0.5Al0.5N. The chemical strengthening is most pronounced for Ta and Nb, although also causing smallest elastic distortions of the lattice due to their atomic radii being comparable with Ti and Al. This is further supported by the analysis of the electronic density of states. Finally, mixing enthalpy as a measure of the driving force for decomposition into the stable constituents is enhanced by adding Y, Zr, and Nb, suggesting that the onset of spinodal decomposition will appear in these cases for lower thermal loads than for Hf and Ta alloyed Ti1−xAlxN.

The influence of transition metal solutes on the dislocation core structure and values of the Peierls stress and barrier in tungsten

Several transition metals were examined to evaluate their potential for improving the ductility of tungsten. The dislocation core structure and Peierls stress and barrier of 1/2〈111〉 screw dislocations in binary tungsten–transition metal alloys (W1−xTMx) were investigated using density functional theory calculations. The periodic quadrupole approach was applied to model the structure of the 1/2〈111〉 dislocation. Alloying with transition metals was modeled using the virtual crystal approximation and the applicability of this approach was assessed by calculating the equilibrium lattice parameter and elastic constants of the tungsten alloys. Reasonable agreement was obtained with experimental data and with results obtained from the conventional supercell approach. Increasing the concentration of a transition metal from the VIIIA group, i.e. the elements in columns headed by Fe, Co and Ni, leads to reduction of the C′ elastic constant and increase of the elastic anisotropy A = C44/C′. Alloying W with a group VIIIA transition metal changes the structure of the dislocation core from symmetric to asymmetric, similarly to results obtained for W1−xRex alloys in the earlier work of Romaner et al (2010 Phys. Rev. Lett. 104 195503). In addition to a change in the core symmetry, the values of the Peierls stress and barrier are reduced. The latter effect could lead to increased ductility in a tungsten-based alloy. Our results demonstrate that alloying with any of the transition metals from the VIIIA group should have a similar effect to alloying with Re.