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In situ growth of pyrochlore iridate thin films has been a long-standing challenge due to the low reactivity of Ir at low temperatures and the vaporization of volatile gas species such as IrO3(g) and IrO2(g) at high temperatures and high PO2. To address this challenge, we combine thermodynamic analysis of the Pr-Ir-O2 system with experimental results from the conventional physical vapor deposition (PVD) technique of co-sputtering. Our results indicate that only high growth temperatures yield films with crystallinity sufficient for utilizing and tailoring the desired topological electronic properties and the in situ synthesis of Pr2Ir2O7 thin films is fettered by the inability to grow with PO2 on the order of 10 Torr at high temperatures, a limitation inherent to the PVD process. Thus, we suggest techniques capable of supplying high partial pressure of key species during deposition, in particular chemical vapor deposition (CVD), as a route to synthesis of Pr2Ir2O7.

Oxygen (O) is an inevitable impurity in bulk metallic glasses (BMGs) and its influence over the glass-forming ability (GFA) of BMGs is a longstanding controversy. The present ab initio molecular dynamics (AIMD) simulations indicate that the GFA decreases upon introducing 0.78 at. pct O in the amorphous Zr55Cu55Al9Be9 (at. pct), while examining the evolution of atomic configurations and kinetic properties in BMGs. This study includes a comprehensive analysis using pair correlation function (PCF), bond pair analysis (BPA), and Voronoi polyhedra construction. It is concluded that the incorporation of O leads to a decline in the closely packed icosahedral polyhedrons, where the atom O is coordinated with Be and Zr in the first nearest shell to form the O-centered clusters with enhanced ordering. Mean square displacement (MSD) analysis also shows that the trace O could induce remarkable acceleration of atomic mobility, therefore increasing crystallization tendency of the Zr55Cu55Al9Be9 alloy. The present results illuminate the role of O in the metallic glass-forming process and reveal the underlying role of O in the GFA of the Zr-Cu amorphous alloys.

Atomic structure, diffusivity and viscosity of Al1-xMgx (x=0, 0.0039, 0.1172, 0.9180, 0.9961, 1)melts at 875, 1000, 1125, and 1250K were investigated by the ab initio molecular dynamics (AIMD) simulations. The simulated results are compared with available experimental and calculated data in the literature with reasonable agreements. Considering the results of pair correlation function g(r), it can be observed that Mg atoms in Al0.8828Mg0.1172 melt aggregate more obviously at 1000 and 1250K. For Al0.0820Mg0.9180, Al atom segregation is more obvious at 875 and 1000K. The tracer diffusion coefficients of Al or Mg in Al1-xMgx (x=0.1172, 0.9180) melts, and interdiffusion coefficients of Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts are all close to the self-diffusion coefficients of Al or Mg. With the increasing temperature, the diffusivity increases linearly. In dilute melts, the tracer diffusion coefficients of solute atom and the interdiffusion coefficients increase nonlinearly with the increasing temperature. For Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts, the viscosities ? are comparatively higher than pure melts. The viscosities of all melts decrease with the increasing temperature, then increase at 1250K. The results obtained in the present work provide an insight into the design of Al and Mg alloys.

Thermodynamics of ferroelectric materials and their ferroelectric to paraelectric (FE-PE) transitions including those in PbTiO3 is commonly described by the phenomenological Landau theory and more recently by effective Hamiltonian and various potentials, all with model parameters fitted to experimental or theoretical data. Here we show that the zentropy theory, which considers the total entropy of a system as a weighted sum of entropies of configurations that the system may experience and the statistical entropy among the configurations, can predict the FE-PE transition without fitting parameters. For PbTiO3, the configurations are identified as the FE configurations with 90- or 180-degree domain walls in addition to the ground state of the FE configuration without domain wall. With the domain wall energies predicted from first-principles calculations based on the density functional theory in the literature as the only inputs, the FE-PE transition for PbTiO3 is predicted showing remarkable agreement with experiments, unveiling the microscopic fundamentals of the transition.

Metallic amorphous/crystalline (A/C) nanolaminates exhibit excellent ductility while retaining their high strength. However, the underlying physical mechanisms and the resultant structural changes during plastic deformation still remain unclear. In the present work, the structure-property relationship of CuZr/Cu A/C nanolaminates is established through integrated high-throughput micro-compression tests and molecular dynamics simulations together with high-resolution transmission electron microcopy. The serrated flow of nanolaminates results from the formation of hexagonal-close-packed (HCP)-type stacking faults and twins inside the face-centered-cubic (FCC) Cu nano-grains, the body-centered-cubic (BCC)-type ordering at their grain boundaries, and the crystallization of the amorphous CuZr layers. The serration behavior of CuZr/Cu A/C nanolaminates is determined by several factors, including the formation of dense dislocation networks from the multiplication of initial dislocations that formed after yielding, weak-spots-related configurational-transitions and shear-transition-zone activities, and deformation-induced devitrification. The present work provides an insight into the heterogeneous deformation mechanism of A/C nanolaminates at the atomic scale, and mechanistic base for the microstructural design of self-toughening metallic-glass (MG)-based composites and A/C nanolaminates.

This article presents a brief review of our case studies of data-driven Integrated Computational Materials Engineering (ICME) for intelligently discovering advanced structural metal materials, including light-weight materials (Ti, Mg, and Al alloys), refractory high-entropy alloys, and superalloys. The basic bonding in terms of topology and electronic structures is recommended to be considered as the building blocks/units constructing the microstructures of advanced materials. It is highlighted that the bonding charge density could not only provide an atomic and electronic insight into the physical nature of chemical bond of materials but also reveal the fundamental strengthening/embrittlement mechanisms and the local phase transformations of planar defects, paving a path in accelerating the development of advanced metal materials via interfacial engineering. Perspectives on the knowledge-based modeling/simulations, machine-learning knowledge base, platform, and next-generation workforce for sustainable ecosystem of ICME are highlighted, thus to call for more duty on the developments of advanced structural metal materials and enhancement of research productivity and collaboration.

The present work examines the effect of alloying elements (denoted X) on the ideal shear strength for 26 dilute Ni-based alloys, Ni$_{11}$X, as determined by first-principles calculations of pure alias shear deformations. The variations in ideal shear strength are quantitatively explored with correlational analysis techniques, showing the importance of atomic properties such as size and electronegativity. The shear moduli of the alloys are affirmed to show a strong linear relationship with their ideal shear strengths, while the shear moduli of the individual alloying elements were not indicative of alloy shear strength. Through combination with available ideal shear strength data on Mg alloys, a potential application of the Ni alloy data is demonstrated in the search for a set of atomic features suitable for machine learning applications to mechanical properties. As another illustration, the predicted Ni ideal shear strengths play a key role in a predictive multiscale framework for deformation behavior of single crystal alloys at large strains, as shown by simulated stress-strain curves., Comment: Associated data at https://doi.org/10.5281/zenodo.5497912

Effect of solutes of transition metals (TM = Cr, Fe, Hf, Mn, Mo, Nb, Ni, Pt, Rh, Ru, Re, Ta, Ti, V, W, Y and Zr) on the local phase transition between the L12 and D019 structures in superlattice intrinsic stacking fault (SISF) of Co3TM has been investigated. All the models employed herein, i.e. (1) the SISF-containing supercell, (2) the axial nearest-neighbor Ising (ANNI) model, and (3) both the L12- and D019-containing (L12 + D019) supercell, yield the same result regarding the stability of SISF in L12-type Co3TM. In the view of bonding charge density, the atomic and electronic basis of local D019 phase transition in the SISF fault layers of Co3TM are revealed. Especially, the negative SISF energy predicted by the L12 + D019 model suggests that both the SISF fault layers (i.e. the local D019 structure) and the L12 phase of Co3TM can be stabilized through a coupling interaction between the fault layers and the solutes, paving a pathway to stabilize Co-base superalloys via Co3TM precipitate. Moreover, the consist results of ESISF via the ANNI model with the classical SISF-supercell method utilized in first-principles calculations supports the approach to efficiently distinguish various planar faults and predict their corresponding energies, such as SISF, superlattice intrinsic stacking fault, anti-phase boundaries, and so on.

A thermodynamic understanding of Seebeck coefficient was demonstrated in terms of electrochemical potential. It divided the contributions to the Seebeck coefficient into two contributions: the effect of thermal electronic excitations due to Fermi distribution and the effect of charge carrier gradient due to thermal expansion. The procedure is illustrated within the rigid band approximation in terms of the electronic density-of-states and the quasiharmonic approximation in terms of the phonon density-of-states. Numerical results were given using the n-type high temperature thermoelectric material La3-xTe4 at x = 0, 0.25, and 0.33 as the prototype at a variety of carrier concentrations.

NiSn4 grows in diffusion couples (Ni plates with electrodeposited Sn) in a temperature range from room temperature up to 353 K. Previously, the crystal structure of NiSn4 grown at ambient temperature was identified to be an intermediate stacking variant between the orthorhombic PtSn4-type and the tetragonal β-IrSn4-type structure, with a slight tendency towards the tetragonal type (Schimpf et al., Mater. Design 109 (2016) 324–333). Now it is reported that NiSn4 forming at 333 K and above, exhibits a 12-layer polytype (space group P42/nbc, a = b = 6.250 A, c = 69.00 A) due to ordered incorporation of stacking faults into the structure. This NiSn4 structure was derived by comparison of its diffraction patterns with those of the exhaustively generated NiSn4 polytypes. First-principles calculations on a series of selected NiSn4 polytypes demonstrate that the experimentally observed polytype is energetically favoured as compared to others.

The thermodynamic properties and phase stability of the Ba-Bi system are investigated computationally and experimentally in the present work. The enthalpies of formation and the finite temperature thermodynamic properties of seven compounds are predicted by first-principles calculations based on density functional theory (DFT), indicating five compounds (BaBi3, Ba11Bi10, Ba4Bi3, Ba5Bi3, and Ba2Bi) to be stable. Phase relations at 773 K and 858 K with composition xBa = 0.90 are established by isothermal annealing and powder X-ray diffraction (XRD) to clarify the previously observed phase transition at 796 K. The extremely low chemical activity of Ba in liquid for a wide range of temperatures and compositions indicates very strong short-range ordering in the liquid phase which is modeled in the present work by introducing the Ba4Bi3 and BaBi3 associates in the liquid phase. Both thermodynamic and phase equilibrium data are then used to evaluate the model parameters in Gibbs energy functions of the five stable compounds and three solution phases of liquid, bcc, and rhombohedral phases by the CALPHAD (CALculation of PHAse Diagram) technique. The present work shows that the Ba-Bi system consists of three eutectic reactions, two peritectic reactions, one peritectoid reaction, and two congruent reactions, as well as that the concentrations of associates are very high in the liquid phase with very low concentration of atomic Ba, which provides the fundamental understanding as to why Bi can be used to remove Ba ions from molten salt solutions.

Long periodic stacking ordered (LPSO) phases have been reported to enhance the strength and ductility of Mg alloys due to their high elastic properties. In the present work, the effects of atomic arrangements in terms of Gd-Al L12-type clusters on LPSOs' elastic properties in the Mg-Gd-Al system were studied using first-principles calculations. Four types of LPSO phases (10H, 18R, 14H, and 24R) were investigated with and without an interstitial atom in the center of the L12-type clusters. It was observed that the elastic stiffness components of the LPSO phases such as C11, C33 and C66 are closely related to the bonding distances of L12 cluster. Furthermore, the interstitial atom within the L12 cluster plays an important role in affecting the elastic stiffness constants of LPSOs, resulting in an increase of C11 and C33 due to the bonding distances of L12 cluster.

Interatomic bonding strength/energy can be quantified by stretching force constants (SFC) after first-principles phonon calculations. Here, we show that the slow-growing alumina (α-Al 2 O 3 ) scale mediated by reactive elements (REs) can be understood via the strong RE O bonding energy from the present SFC model applied to oxides (Al 2 O 3 , Cr 2 O 3 , Ti 2 O 3 , ZrO 2 , HfO 2 , Y 2 O 3 , and La 2 O 3 ), Al 3 M, and Al 47 MO 72 (M = Cr, Ti, Zr, Hf, Y, and La). The present model indicates that Hf is the best RE in retarding alumina scale growth, agreeing with the analyses from bulk modulus, melting point, and enthalpy of formation of oxides, and experimental observations.

An extensive first-principles quasiharmonic phonon calculation was carried out for the thermoelectric material La3−xTe4 at the compositions of x = 0.0, 0.25 and 0.33, focusing at the La site vacancy effects on the thermodynamic properties. The calculated quantities include the 0 K static total energy curves and electronic band structures as well as density-of-states, the phonon density-of-states, together with the linear thermal expansion coefficients, the entropies, the enthalpies, the heat capacities, the bulk moduli, and the Debye temperature as functions of temperature up to 1200 K. Both the standard Perdew-Burke-Ernzerhof (PBE) and the Perdew-Burke-Ernzerhof revised for solids (PBEsol) exchange-correlational functionals were examined and it was found that the PBEsol functional was generally better than the PBE functional in describing both the crystal and electronic properties for the La3−xTe4.

Titanium alloys are great implant materials due to their mechanical properties and biocompatibility. However, a large difference in Young’s modulus between bone (∼10–40 GPa) and common implant materials (ie. Ti-6Al-4V alloy ∼110 GPa) leads to stress shielding and possible implant failure. The present work predicts the single crystal elastic stiffness coefficients (cij’s) for five binary systems with the body centered cubic lattice of Ti-X (X = Mo, Nb, Ta, Zr, Sn) using first-principles calculations based on Density Functional Theory. In addition, the polycrystalline aggregate properties of bulk modulus, shear modulus, Young’s modulus, and Poisson ratio are calculated. It is shown that the lower Young’s modulus of these Ti-alloys stems from the unstable bcc Ti with a negative value of (c11–c12). The data gathered from these efforts are compared with available experimental and other first-principles results in the literature, which set a foundation to design biocompatible Ti alloys for desired elastic properties.

A systematic study of the stacking fault energy (?SF) for the dilute Al-based alloys (Al23X, Al47X and Al71X, where X = Al, Ag, Be, Ca, Cd, Co, Cu, Cr, Fe, Ga, Ge, Hf, In, K, La, Li, Mn, Mg, Ni, Na, Pb, Sc, Sn, Sr, Si, Ti, V, Zn, and Zr) has been performed by means of first-principles calculations. Alias shear deformation is adopted in the present investigations. The presently calculated ?SF for Al is in favorable accordance with experimental and other theoretical data. For the targeted elements, the calculations indicate that Na, Si, K, Ca, Sc, Ga, Ge, Sr, Zr, In, Sn, La, Hf, and Pb, in any concentration we considered, decrease the ?SF of Al, while Ag, Be, Cd, Co, Cu, Cr, Fe, Li, Mn, Mg, Ni, Ti, V, and Zn increase the ?SF of Al, when the concentration of alloying elements is 1.39 at. % in the system. With increasing concentration of alloying elements, Li, Mg, V, Ti, and Cd change from increasing the ?SF of Al to decreasing it, based on present investigations. Among the alloying elements, which decrease the ?SF of Al, La decreases the ?SF most significantly. It is also found that the ?SF of Al-X generally decreases with the increase of equilibrium volume. The results obtained in the present work provide an insight into the design of Al based alloys.

Titanium alloys are being investigated as suitable materials for load-bearing implants because of their biocompatibility and mechanical properties. Stress shielding, a common issue with the current load-bearing implant materials, occurs due to a Young’s modulus (E) mismatch between bone (∼10–40 GPa) and implants (such as Ti-6Al-4V ∼110 GPa), which leads to bone dying around the implant and ultimately implant failure. Reducing the Young’s modulus of Ti alloys may overcome the issues of stress shielding and improve implant materials. In the present work, first-principles calculations have been used to predict the single crystal elastic stiffness coefficients (cij’s) for the Ti-containing ternary alloys Ti-X-Y (X ≠ Y = Mo, Nb, Sn, Ta, Zr) in the bcc lattice. It is found that the ternary Ti-X-Y (X ≠ Y = Mo, Nb, Ta) alloys behave similarly; so do the ternary Ti-X-Sn (X = Mo, Nb, Ta) alloys and the Ti-X-Zr (X = Mo, Nb, Ta) alloys. This is expected due to the similarity between the Mo, Nb and Ta elements. The results also show that the Ti-Zr-X alloys stabilized the bcc phase at lower alloying concentrations. The polycrystalline aggregate properties are also estimated from the cij’s, including bulk modulus, shear modulus and Young’s modulus. The results show that Ti-alloys with compositions close to the bcc stability limit have the lowest E. In combination with previous predictions, a complete elastic database has been established using the CALPHAD (CALculation of PHAse Diagram) based modeling approach. The database results are compared with the E of higher order Ti alloys and shown to be able to predict the E accurately. This complete database forms a foundation to tailor Ti alloys for desired elastic properties.

The diffusion of interstitial oxygen (O) in fcc aluminum (Al) has been studied using first-principles and the diffusion coefficient has been calculated. Whereas interstitial atoms in fcc systems are typically found to hop directly between interstitial centres, the diffusion pathway for interstitial O in fcc Al was calculated to have a curved minimum energy pathway with an energy barrier of 0.95 eV. The barrier was found to be off-centre of a neighboring octahedral site. Also unlike the majority of fcc metals, O prefers to sit in the tetrahedral interstitial site as opposed to the octahedral site. The calculated O diffusion coefficient is on the same order of magnitude of the diffusion coefficient of O in other fcc metals. The preferred interstitial site, diffusion pathway and vacancy binding energy were found to be related to the bond length of O with neighboring Al atoms.

Bulk and surface properties of oxygen in cubic c-Cr0.5Al0.5N were investigated through first-principles calculations based on density functional theory (DFT) in the present work. It was observed that the (0 0 1) surface of c-Cr0.5Al0.5N terminated with Cr-Al-N is energetically favorable. Calculations of oxygen adsorbed on the (0 0 1) surface show that O is bonding with Cr preferentially instead of Al due to the stronger Cr-O bond strength in comparison with that of Al-O. The difference charge density and electronic density of states indicate that the electrons shared between O and Cr and hybridization between the O-p and Cr-d orbitals contribute to the formation of strong Cr-O bonding on the surface. An oxidation mechanism is proposed, i.e. the Cr-O bond is first established, resulting in the formation of α-Cr2O3, and subsequent incorporation of α-Al2O3 promotes the formation of a mixed (Cr, Al)2O3 scale.

Refractory high-entropy alloys present attractive mechanical properties, i.e., high yield strength and fracture toughness, making them potential candidates for structural applications. Understandings of atomic and electronic interactions are important to reveal the origins for the formation of high-entropy alloys and their structure−dominated mechanical properties, thus enabling the development of a predictive approach for rapidly designing advanced materials. Here, we report the atomic and electronic basis for the valence−electron-concentration-categorized principles and the observed serration behavior in high-entropy alloys and high-entropy metallic glass, including MoNbTaW, MoNbVW, MoTaVW, HfNbTiZr, and Vitreloy-1 MG (Zr41Ti14Cu12.5Ni10Be22.5). We find that the yield strengths of high-entropy alloys and high-entropy metallic glass are a power-law function of the electron-work function, which is dominated by local atomic arrangements. Further, a reliance on the bonding-charge density provides a groundbreaking insight into the nature of loosely bonded spots in materials. The presence of strongly bonded clusters and weakly bonded glue atoms imply a serrated deformation of high-entropy alloys, resulting in intermittent avalanches of defects movement. A cluster-and-glue model of atomic arrangements explains the yield strength and mechanical response of high entropy alloys. Inspired by metallic glass, a team led by William Yi Wang at China’s Northwestern Polytechnical University and collaborators in the United States of America used molecular dynamics to build different atomic arrangements of refractory high entropy alloys consisting of four or more elements. Depending on atomic size and the periodic table group of each atom, some atoms organized into clusters while others glued the clusters together. Chemical bonds broke and formed with plastic deformation as the alloys went from one atomic arrangement to another via the glue atoms, causing defect avalanches explaining the serrated mechanical response of high entropy alloys. Taking into account atomic arrangement may thus help us predict the properties of high entropy alloys.

Phase stability, elastic, and thermodynamic properties of (Co,Ni)3(Al,Mo,Nb) with the L12 structure have been investigated by first-principles calculations. Calculated phonon density of states show that (Co,Ni)3(Al,Mo,Nb) is dynamically stable, and calculated elastic constants indicate that (Co,Ni)3(Al,Mo,Nb) possesses intrinsic ductility. Young’s and shear moduli of the simulated polycrystalline (Co,Ni)3(Al,Mo,Nb) phase are calculated using the Voigt–Reuss–Hill approach and are found to be smaller than those of Co3(Al,W). Calculated electronic density of states depicts covalent-like bonding existing in (Co,Ni)3(Al,Mo,Nb). Temperature-dependent thermodynamic properties of (Co,Ni)3(Al,Mo,Nb) can be described satisfactorily using the Debye–Gruneisen approach, including heat capacity, entropy, enthalpy, and linear thermal expansion coefficient. Predicted heat capacity, entropy, and linear thermal expansion coefficient of (Co,Ni)3(Al,Mo,Nb) show significant change as a function of temperature. Furthermore the obtained data can be used in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys.

The S-Se system is the key to many chalcogenide alloys. A thermodynamic model of the S–Se system is formulated using an integrated approach of first-principles calculations and the CALculation of PHAse Diagram (CALPHAD) method, which is used to predict the vapor-liquid-solid S-Se phase diagram. An existing first-principles approach is modified through considering the contribution from the acoustic Gruneisen parameters to the thermodynamic properties, enabling more accurate prediction of thermodynamic properties of crystals with large unit cells. The approach is applied to all the stable and metastable phases with complex molecule structures within the S-Se system with the exception of an intermediate phase due to its unknown structure. The prediction of the transition temperature between α-S and β-S (428 K) is close to the experimental value (369 K). Given the high complexity of solid solutions containing multiple molecular species, two models based on homogeneous and randomly substituted species are constructed and applied to give an interval estimation of solid mixing enthalpies. The CALPHAD approach is applied using both selected experimental measurements and thermodynamic properties predicted by first-principles calculations, reproducing experimental data and predictions reasonably well.

First-principles calculations have been performed to investigate the phase stability, elastic, and thermodynamic properties of Co 3 (Al,Mo,Nb) with the L1 2 structure. Calculated elastic constants show that Co 3 (Al,Mo,Nb) is mechanically stable and possesses intrinsic ductility. It is found that the shear and Young's moduli of Co 3 (Al,Mo,Nb) are smaller than those of Co 3 (Al,W). Calculated density of states indicate the existence of covalent-like bonding in Co 3 (Al,Mo,Nb). Temperature-dependent thermodynamic properties of Co 3 (Al,Mo,Nb) can be described satisfactorily using the Debye-Gruneisen approach, including entropy, enthalpy, heat capacity and linear thermal expansion coefficient, showing their significant temperature dependences. Furthermore the obtained data can be employed in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys.

Nano-porous materials are spreading widely in various fields, such as electrochemistry, biochemistry, adsorption, and catalysis. In the present work, nano-porous γ-Al2O3 layers with 200 nm thickness have been fabricated on porous Ti-48Al-6Nb alloys by soaking in NaOH solution. Corrosion products of γ-Al2O3 with 200 nm thickness form after 48 h and begin to transform to nano-porous structures at 72 h in the areas with a smaller radius of curvature. Then the nano-pores shrink and reach the final size of 60 ± 10 nm within 120 h. Increasing the concentration of NaOH solution or soaking time accelerates the formation of nano-porous layers and the best situation is soaking for 120 h in a 2.0 mol/L NaOH solution. Meanwhile, the nano-porous γ-Al2O3 layers improve the electrochemical corrosion resistance of the porous alloys due to the more positive self-corrosion potential/current and the right-moved passive region. The NaOH corrosion method to fabricate nano-porous γ-Al2O3 layers is much easier than other methods and the porous alloys possess the better corrosion resistance and absorbability thanks to the nano-porous γ-Al2O3 layers and the micron-porous Ti-48Al-6Nb matrix. Keywords: Porous TiAl alloys, Nano-porous, γ-Al2O3, Total pore area, Polarization

Pugh’s criterion in terms of the bulk/shear modulus ratio ( B / G ) is widely used to distinguish the ductility and brittleness of metals, with the recommended B / G ratio of 1.75 for the boundary ratio between ductility and brittleness. The present first-principles calculations yield a B / G = 3.69 for the C15 Laves phase NbCr 2 , suggesting the ductility of NbCr 2 according to Pugh’s criterion. However, experiments indicate that NbCr 2 is a brittle phase at room temperature with the fracture toughness of 1.0–1.4 MPa m 1/2 . NbCr 2 is hence a compound with its ductile and brittle behavior beyond Pugh’s criterion, and this finding also validates for other Laves phases and compounds. New insight into Pugh’s B / G criterion is also discussed.

In this work, the effects of Mn on lattice parameter, electron work function (EWF), bonding charge density, and hardness of nanocrystalline Al Mn non-equilibrium solid solutions are investigated. We show how the enhancement of the EWF contributes to the observed improvement of the hardness of Al Mn solid solutions. It is understood that the physical mechanisms responsible in our model, using the EWF coupled with a power law scaled hardness, are attributed to the redistribution of electrons caused by the presence of Mn solute atoms, supporting an atomic and electronic basis for the coupling of solid solution and grain refinement strengthening mechanisms.

The influence of various transition alloying elements (X's) on the elastic properties of W-based alloys has been studied via first-principles calculations on the basis of density functional theory. Here, nineteen transition metal alloying elements (X) are considered: Ti, V, Cr, Fe, Co, Ni, Y, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, Re, Os, Ir, and Pt. It is found that (i) the bulk modulus of the dilute W-X alloy decreases with increasing its equilibrium volume, particularly, for the alloying elements in the same period; (ii) all of the alloying elements decrease the shear modulus of BCC W; and (iii) the largest decrease of elastic properties of W is due to alloying element Y. In addition, it is shown that the changes of elastic properties of W caused by the alloying elements are traceable from the electron charge density distribution, resulting in a bonding distortion between W and the alloying atoms. Using the quasi-static approach based on the Debye model, the elastic properties of these W-X alloys at finite temperatures are predicted. Calculated properties of BCC W and the W-X alloys are in favorable agreement with available experimental measurements.

A new relationship among self- and impurity diffusion coefficients has been proposed for binary solution phases and verified via 30 solid solutions. In terms of this model, one impurity diffusion coefficient in a binary phase can be predicted once the other three diffusion coefficients are available. The application of the present model is exemplified in the Al-Mg system.

A complete first-principles thermodynamic model was developed and applied to hexagonal close-packed structure e -Fe3N. The electronic structure was calculated using density functional theory and the quasiharmonic phonon approximation to determine macroscopic thermodynamic properties at finite temperatures was generalized in terms of the partition function for any lattice of interest. Specially, thermal expansion of the hexagonal close-packed e phase with two independent lattice parameters was studied by means of the present model and first-principles phonon calculations. The present predictions of thermal expansion of e -Fe3N are in good agreement with experimental data.

High-Nb containing (6–10 at.%) TiAl alloys exhibit excellent high-temperature strength and oxidation resistance. However, they are difficult to be fabricated into sheet in comparison with the conventional TiAl alloys. In the present work, the hot-deformation behavior of a high Nb–TiAl alloy (Ti–45Al-8.5Nb-0.2W-0.2B-0.03Y) was investigated. Hot-rolling process was optimized and carried out directly from the PAM (Plasma Arc Melting) ingot without the hot isostatic pressing (HIP) and hot forging. The hot-rolled sheets were successfully manufactured with dimensions up to 360 mm × 100 mm × 3.5 mm. The microstructure of as-rolled sheet is a typical “near gamma” characteristic with an average grain size about 15 μm. In the view of breakdown the lamellar colonies of high Nb–TiAl alloy ingot, the direct hot-rolling process has advantage over hot can forging and extrusion. Moreover, mechanical properties at room and high temperatures were also tested. Noteworthily, the as-rolled high Nb–TiAl alloy shows superplasticity above 950 °C at relatively high strain rate of 5 × 10−4.

High-quality epitaxial growth of inter-metallic MnPt films on oxides is achieved, with potential for multiferroic heterostructure applications. Antisite-stabilized spin-flipping induces ferromagnetism in MnPt films, although it is robustly antiferromagnetic in bulk. Moreover, highly ordered antiferromagnetic MnPt films exhibit superiorly large exchange coupling with a ferromagnetic layer.

Topological materials are derived from the interplay between symmetry and topology. Advances in topological band theories have led to the prediction that the antiperovskite oxide Sr3 SnO is a topological crystalline insulator, a new electronic phase of matter where the conductivity in its (001) crystallographic planes is protected by crystallographic point group symmetries. Realization of this material, however, is challenging. Guided by thermodynamic calculations, a deposition approach is designed and implemented to achieve the adsorption-controlled growth of epitaxial Sr3 SnO single-crystal films by molecular-beam epitaxy (MBE). In situ transport and angle-resolved photoemission spectroscopy measurements reveal the metallic and electronic structure of the as-grown samples. Compared with conventional MBE, the used synthesis route results in superior sample quality and is readily adapted to other topological systems with antiperovskite structures. The successful realization of thin films of Sr3 SnO opens opportunities to manipulate topological states by tuning symmetries via strain engineering and heterostructuring.

A peculiar checkerboard microstructure has been observed in as-cast Mo-rich Al–Mo–Ti alloys with slightly less than 75 at.% Al. It contains a Mo-rich tetragonal D022-Al3Ti phase as well as an orthorhombically distorted variant thereof, with a somewhat higher Mo content, referred to as D022’. Both phases are fcc-based superstructures originating mainly from ordering of transition metal (TM) vs. Al. The measured lattice parameters of the D022’ phase were evaluated using strain tensors quantifying the strain with respect to some average fcc substructure. Thereby, it was shown that the D022’ structure possesses some common features with the binary Al8Mo3 and Al3Mo fcc-based superstructures known from the Al–Mo system. It is made likely that D022’ as well as Al8Mo3 and Al3Mo (with Mo being a group-vi transition metal) are some continuation of the series of structures observed for Al3TM with TM from group iii via iv to v with increasing average number of electrons per atom. This view is supported by first-principles calculations which indicate elastic instability of a hypothetical D022-Al3Mo structure towards an orthorhombically distorted structure. The checkerboard microstructure likely forms directly after solidification from a homogeneous D022 structure by decomposition into Mo-richer (D022’) and -poorer regions. The phase interface orientations can be reconciled with the deformation necessary to transform D022 into D022’. Further annealing at elevated temperatures leads to decomposition of the microstructures, resulting in formation of Al8Mo3 and Mo-depleted D022, indicating that the D022’ phase is metastable.

In this work, ab initio molecular dynamic simulations investigate diffusivities of Ni and Al in Ni50Al50 melt under high pressures. While the tracer diffusion coefficients at the equilibrium state predicted by Green-Kubo and the Einstein equations follow the Arrhenius relationship and agree well with the experimental and theoretical results, a linear relationship between the logarithm of tracer diffusion coefficients and the external pressure is addressed in term of an activation volume modified Arrhenius relations. It is understood that the autocorrelation velocity functions (VACF) characterizes the capacity of an atom memorizing the velocity, which has also been considered as one of important approaches revealing thermodynamics, kinetics and structure relaxation dynamics of melts. The onset of the negative region of VACF is in line with the plateau of the meaning square displacement representing the cage effect of the system. The initial damping oscillations of VACFs are due to the momentum relaxation caused by the collision between the tagged atoms and its neighbor ones while the subsequent rises result from the energy relaxation. This work provides an insight into the physical factors controlling these dynamic behaviors under extreme conditions of Ni-Al, which could be extended to the other advanced materials.

An integrated experimental and computational approach has been adopted to investigate the formation mechanism of intermetallic compounds (IMCs) in dissimilar Al-Cu joints processed by vaporizing foil actuator welding (VFAW). Aiming to understand the formation of IMCs and their transition, the present work employed first-principles calculations of thermodynamic properties as a function of temperature and pressure together with diffusivities of Al and Cu from the literature. Agreeing with experimental observations, the predicted IMC formation sequence in the low-energy welding region is as follows. θ-Al2Cu forms first due to the fast diffusivity of Cu in the Al-matrix. θ-Al2Cu then transforms to η2-AlCu because of the fast diffusivities of Al/Cu in θ-Al2Cu. In the high-energy welding region, the stable γ1-Al4Cu9 and the metastable θ’’-Al3Cu are also formed in addition to the aforementioned θ-Al2Cu and η2-AlCu. η2-AlCu and considerable γ1-Al4Cu9 are the major phases in the high-energy welding region. The present approach, combining experiments and calculations, is proven to be a practical way to understand non-equilibrium metallurgical processes, as demonstrated through the study of VFAW Al-Cu joints. Keywords: Vaporizing foil actuator welding (VFAW), Al-Cu intermetallic compounds, Thermodynamic properties, Diffusion, First-principles and phonon calculations

Phase equilibria in the Ti–Al–V system at 1300 °C were studied experimentally by examining 50 samples with compositions up to 75 at % Al. An isothermal section of Ti–Al–V at 1300 °C was constructed by means of X-ray diffraction (XRD), electron backscattered diffraction (EBSD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The isothermal section is characterized by five single-phase regions (i.e., α phase with hcp_A3 structure, β phase with bcc_A2 structure, γ phase with L10 structure, δ phase with D82 structure, and e phase with D022 structure) and three three-phase regions (α+γ+e, α+δ+e, and α+β+δ). Compared with the tentative results at 1200 °C, the single α phase at 1300 °C is highly extended, while the other single-phase regions remain almost unchanged, resulting in the emergence of new three-phase regions.

In the present work, the phase equilibria of the Nb-Ni-Ru system at 1100 °C were investigated via a combination of triple diffusion and equilibrated alloys. The samples were examined by X-ray diffraction and electron probe microanalysis. Three new ternary compounds, namely, τ1 (Nb5Ni13Ru2), τ2 (Nb(Ni1-xRux)3, 0.17 ≤ x ≤ 0.32) and τ3 (Nb(Ni1-xRux)3, 0.34 ≤ x ≤ 0.67), were discovered. The isothermal section of the Nb-Ni-Ru ternary system at 1100 °C consists of 10 single-phase regions, 20 two-phase regions, and 11 three-phase regions. The homogeneity ranges for phases in this system were established. In addition, the phases of the Nb-Ru binary system at 1100 °C were discussed, and the existence of compounds NbRu and NbRu2 was confirmed. The NbRu3 phase was not identified, but it should be the solid solution of Nb in Ru.

Ti–48Al–6Nb porous alloys were synthesized by the powder metallurgy (PM) method, and the associated phase transformation and pore parameter were investigated in order to reveal the pore-formation mechanism. The present results indicate that the Nb–Al and Ti–Al phase transformations contribute to the pore-formation. It was found that the five-step phase transformations for the Ti–48Al–6Nb porous alloys occur as follows: (1) Ti + Al → TiAl3 at 600–700 °C; (2) Nb + Al → NbAl3 at 700–900 °C; (3) TiAl3 + Ti → TiAl at 900–1100 °C; (4) TiAl + Ti → Ti3Al/TiAl at 1100–1350 °C; (5) NbAl3 + Nb → Nb2Al and the Ti3Al turns to the major phase at 1350 °C. These phase transformations made the pore-diameter increasing continuously from 1.71 μm to 12.10 μm and also made the pore volume distributing widely. At the second step of 700–900 °C, the Nb–Al phase transformation leads to 5% more volume expansion compared to the Ti–Al based porous alloys. Meanwhile, the porosity and total pore area initially increase and then decrease at this step, but they increase intensely at the final step, which is needed as a catalytic carrier. Keywords: Porous materials, Phase transformation, Heat treatment, Powder metallurgy, Microstructure

Elastic anisotropies obtained by density functional theory (DFT) calculations of four iron carbides exhibiting trigonal prismatic coordination of C by Fe are presented and compared. The elastic anisotropy is considerable for the carbides θ-Fe3C, χ-Fe5C2 and a hypothetical Fe2C with Pbcm symmetry, all with sheet-like arrangement of the trigonal prisms which results in a largely parallel arrangement of the prism axes. It is found that the easy shear which is mainly responsible for the large elastic anisotropy in these carbides occurs in all these three carbides in a plane perpendicular to the average axis of the prisms. In contrast to these three elastically anisotropic carbides, Fe7C3, in which the axes of the trigonal prisms are much more regularly distributed in space, shows a negligible elastic anisotropy.

The utility of the Debye–Gruneisen has been investigated with respect to a finite-temperature fitting parameter known as the scaling factor. This scaling factor is studied using bcc, fcc, hcp systems and the Mg–Zn binary system. Predicted Debye temperatures, using a calculated scaling factor, show good agreement with experiments and improvements over the scaling factor derived by Moruzzi et al. Finite-temperature thermodynamic properties of Mg, Zn, Mg4Zn7, MgZn2, and Mg2Zn11 are investigated to show the efficiency and improved accuracy of the calculated scaling factor. For the intermetallic compounds except Mg2Zn11, ΘD predictions are improved upon greatly by implementing a calculated scaling factor. Along the same line, heat capacity is also predicted, showing good agreement with experimental values for these compounds. For Mg2Zn11, the Debye–Gruneisen model cannot account for anomalous lattice dynamics at low temperatures.

High Nb containing TiAl porous alloys were synthesised by powder metallurgy (PM). In order to reveal reaction mechanism of Nb in preparation of the porous alloys, Nb–Al diffusion reaction was investigated using diffusion couples at relatively low temperatures of 600–800°C. The porous Nb–Al diffusion layer was identified as NbAl3 phase and the thickness of diffusion layer indicated that the Nb–Al diffusion mainly occurred at 800°C. In addition, the pore diameter distribution indicated that Nb–Al diffusion also contributed to the increase in pore diameter. According to these results, the diffusion reaction model was established for high Nb containing TiAl porous alloys.

Effects of W on structural evolution and diffusivity of Ni–10W and Ni–20W (at.%) melts are studied via ab initio molecular dynamic simulations. The atomic local topology is characterized in terms of pair correlation functions, structure factors, bond pairs, and topological structures. It is observed that the Ni–20W melt is more closely packed than the Ni–10W, showing higher average coordination number and more Voronoi polyhedra with high coordination numbers. The tracer diffusion coefficients of Ni and W calculated by the mean-squared displacement are very close to each other in both Ni–W alloys. Comparing with their self-diffusion coefficients of pure Ni and pure W, the tracer diffusion coefficient of Ni in Ni–W melts decreases, while that of W increases. Nearly identical tracer diffusivities of Ni and W in Ni–W melts attribute to the formation of local solute-centered polyhedra with high deformation electron density severing as bridges between various atomic clusters and strengthening the atomic bonding, indicating the collective motion of Ni and W in those melts. Moreover, atomic bonds of Ni–W metallic melts characterized by the deformation electron density present the network among different atomic clusters, revealing the physical nature of the collective motions between W and Ni.

Stacking fault energy ( γ SF ) for dilute multicomponent Ni-base alloys has been modeled using an integrating CALPHAD (calculation of phase diagram) modeling approach and first-principles alias shear deformation calculations of unary, binary, and ternary alloys. The present first-principles results of γ SF from 55 Ni 70 X 1 Y 1 (X and Y are 11 alloying elements of Al, Mo, Nb, Os, Re, Ru, Ta, Tc, Ti, V, and W) indicate that the more the structural similarity between X and Y, the smaller the ternary interaction of γ SF ; and the variation of γ SF due to alloying elements is similar to that of bulk modulus.

The structural and kinetic properties of Ni have been investigated between 300 and 2700 K using ab initio molecular dynamics within the framework of density–functional theory. Equations of state (EOS) are derived from the constant NVT ensembles with N being the number of atoms, V the volume, and T the temperature. From EOS fitting, the equilibrium volumes of Ni are predicted as a function of temperature, which are in good agreement with available experimental data. It is found that the solid–liquid phase transformation can be evaluated by the internal energy change and validated by the appearance of short-range ordering according to structural analysis. Additionally, the diffusion coefficient and shear viscosity are also predicted, in favorable accord with experimental data.