Intermetallic Materials Research Articles

Capacity fading model for a solid electrolyte interface with surface growth

Many efforts in the area of renewable energies are focused in the development of batteries of electrochemical cells to store energy fulfilling the requirements of high energy and power density. Electrochemical cells based on Li-ions are able to satisfy the requirements of high energy and power density. In general, cell electrode materials based on intermetallic and conversion compounds possess higher capacity to store Li -ions than those based on intercalation compound. Among intermetallic materials, silicon is a very attractive material for anodes of Li -ion cells, since it has a very high gravimetric capacity (3572mAhg−1) compared to graphite (372mAhg−1), being graphite an intercalation material and the most common anode in Li -ion cells. However, the main problem associated to these intermetallic and conversion materials is capacity fading. In this work it is shown how the capacity fading of electrodes based on silicon can be theoretically described by considering a simple model for the solid electrolite interface, where the active surface of the electrode is allowed to increase during the process of lithiation and delithiation.

Spacer strategy for exceptionally low thermal conductivity and high zT in antimony-doped bulk silicon

In this study, the effects of inserting mica into bulk silicon for thermoelectric use on the alloying, nanosize, and spacer effects that are mainly used to suppress thermal conductivity are examined. Results revealed that nanocrystallinity as well as the extremely high doping amount of antimony in the grains drastically enhance the power factor. Dislocations or vacancies can be induced at the nanoscopic level by performing multiple heat treatments and by inserting spacer materials at the bulk level, which in turn can inhibit the heat transport in high thermally conductive materials. Furthermore, a record and reliable figure-of-merit of ∼0.6 at 1173 K is obtained for mica-inserted SiSb0.02, in addition to reduced thermal conductivity (∼6.5 W/m-K). These observations open avenues for silicon and can further lead to the formation of intermetallic, half-Heusler, and other chalcogenide materials.

Divergence of the quadrupole-strain susceptibility of the electronic nematic system YbRu2Ge2

Ferroquadrupole order associated with local [Formula: see text] atomic orbitals of rare-earth ions is a realization of electronic nematic order. However, there are relatively few examples of intermetallic materials which exhibit continuous ferroquadrupole phase transitions, motivating the search for additional materials that fall into this category. Furthermore, it is not clear a priori whether experimental approaches based on transport measurements which have been successfully used to probe the nematic susceptibility in materials such as the Fe-based superconductors will be as effective in the case of [Formula: see text] intermetallic materials, for which the important electronic degrees of freedom are local rather than itinerant and are consequently less strongly coupled to the charge-carrying quasiparticles near the Fermi energy. In the present work, we demonstrate that the intermetallic compound [Formula: see text] exhibits a tetragonal-to-orthorhombic phase transition consistent with ferroquadrupole order of the Yb ions and go on to show that elastoresistivity measurements can indeed provide a clear window on the diverging nematic susceptibility in this system. This material provides an arena in which to study the causes and consequences of electronic nematicity.

(Invited) Na-Ion Batteries: Challenges and Opportunities

With the ever-increasing demands of modern societies, energy generation, storage, and distribution are becoming increasingly important research fields. Currently, one of the most promising areas of research and development is Sodium ion Battery (SIB) technology, which has a range of potential applications but remains particularly suited for use in stationary systems. [1-5]. Here we will discuss SIB systems in terms of what may be considered its three most significant components: anodes, electrolytes, and cathodes. SIB anodes are mainly based on hard carbon materials, due to their attractive combination of low cost and high energy density. However, there has also been interest in other systems, such as intermetallic alloying materials and metal oxides, as well as exploiting specific electrolyte co-solvation effects so as to enable the use of graphite. In general, the SIB research community uses organic electrolytes which are analogous to already existing Lithium ion batteries (LIB). However, recently there has been growing interest in developing new electrolytes which are specifically tailored for use in SIBs, such as optimized liquid and solid electrolytes. At the present time, cathodes are one of the most explored SIB components - with a plethora of options to choose from, including Prussian blue and organic materials. However, the most promising are polyanionic and layered materials, with their good combinations of electrochemical performance, low cost, stability and available constituents. Although interest in SIB technology has only relatively new, when compared to LIBs, it has been already developed at the prototyping level. A general overview of the most interesting electrode and electrolyte materials for Na-ion batteries paying special attention to those related to the current prototypes will be presented. By examining this topic in detail, it will be shown that there exists a strong drive to exploit this technology and that there are a wide range of opportunities to develop new and improved SIB technologies.

Electrochemical Energy Conversion on Intermetallic Compounds: A Review

Structurally ordered intermetallic compounds possess unique chemical and physical properties, making them an interesting class of materials for application in electrocatalytic reactions. This Review comprises the work on intermetallic compounds used for energy relevant electrocatalysis and is structured by the reactions in scope, which are the hydrogen evolution reaction (HER), electrochemical carbondioxide reduction reaction (eCO2RR), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR) as well as the oxidation reactions of formic acid (FAOR), methanol (MOR), and ethanol (EtOR). Optimization pathways for electrocatalysts, based on the adjustability of the intermetallic materials, are highlighted, and experimental data are provided in a comparative manner, to provide an overview, foundation, and reference for further development.

On the prospects of application of nanostructured heterophase polyfunctional composite materials inengine building industry

The paper gives a brief review of properties and applications of developed extra-hard nanostructured composite materials and coatings based on them. The presentresearch suggestsaerospace applications of nanostructured composite materials based on carbides, carbonitrides and diboridesof transition and refractory metals. To improve the technical and economic performance of gas turbine engines, it is advisable to use new composite structural materials whose basic physicomechanical properties are several times superior to traditional ones. The greatest progress in developing new composites should be expected in the area of materials created on the basis of polymer, metal, intermetallic and ceramic matrices. Currently components and assemblies of gas turbine engines and multiple lighting power units with long operation life and durability will vigorously develop. Next-generation composites are studied in all developed countries, primarily in the United States and Japan.

First principles study of surface properties and oxygen adsorption on the surface of Al3Ti intermetallic alloys.

The density functional theory (DFT) method was applied to study the structural, electronic and surface properties of low-index Al3Ti intermetallic materials. The surface energies and electronic structures of those surfaces were also discussed in this study. The calculated surface energies of the low-index surfaces of Al3Ti indicated that nonstoichiometric (110) surface with Al termination was the most stable surface. On this basis, the oxygen adsorption behavior of the (110)-Al surface was further studied to clarify the antioxidant mechanism of Al3Ti intermetallic alloys. Various adsorption sites of oxygen atoms on the (110)-Al surface were considered to identify the most stable adsorption configurations. According to the calculation results of adsorption energies, it was found that stability was maximized when oxygen was adsorbed at the Al–Al bridge site. Meanwhile, a density of state study indicated that adsorption of oxygen on the (110)-Al surface preferred to bond with Al atoms rather than Ti atoms.

High temperature solid-lubricating materials: A review

Abstract This paper provides a review on the current research developments in high temperature solid-lubricating materials. We first briefly discuss fundamental of high temperature solid-lubricating materials, including design strategies of a low friction coefficient, a high wear resistance, a wide environment range, and how to construct high temperature solid-lubricating materials. And then the review highlights progress in the design and exploration of high temperature solid-lubricating coatings (monolithic coatings, multiphase coatings and self-adaptive coatings) and composites (metal, intermetallic and ceramic matrices high temperature solid-lubricating composites). Finally, we shortly introduce practical applications and trends of high temperature solid-lubricating materials in the future. These developments offer new avenues to both intensify the understanding of high temperature tribology and expand the diversity of practical applications.

Paths to Stabilizing Electronically Aberrant Compounds: A Defect-Stabilized Polymorph and Constrained Atomic Motion in PtGa2

The structures and properties of intermetallic phases are intimately connected to electron count; unfavorable electron counts can result in structural rearrangements or new electrical or magnetic behavior when no such transformation is available. The compound PtGa2 appears to teeter on the border between these two scenarios with its two polymorphs: a cubic fluorite type form (c-PtGa2) and a complex tetragonal superstructure (t-PtGa2) whose Pt-Pt connectivity aligns with the 18- n electron counting rule. Here, we investigate the factors underlying this polymorphism. Electronic structure calculations show that the transition to t-PtGa2 opens a pseudogap at the Fermi energy that can be traced to Pt-Pt isolobal bond formation, in line with the 18- n bonding scheme. Conversely, DFT-chemical pressure (CP) analysis reveals a network of positive local pressures along Pt-Ga contacts, requiring that the c-PtGa2 to t-PtGa2 transition follows tightly concerted atomic motions. Experimentally, a series of samples with varying Pt:Ga ratios were synthesized to examine the stability ranges of the polymorphs. Ga-poor samples yield exclusively the cubic polymorph over the full range of temperatures studied, which can be correlated to the enhanced incorporation of interstitial Pt atoms (at points of negative pressure in the CP scheme). At more Ga-rich compositions, however, t-PtGa2 emerges as a low-temperature form. In these samples, the t-PtGa2 to c-PtGa2 transition is found to be reversible, but with a large hysteresis that in single crystals can exceed 100 °C. Together, the theoretical and experimental results indicate that the c-PtGa2 phase is buttressed at its unfavorable electron count by the interstitial atoms and networks of positive CPs that restrict atomic motion, suggesting more general strategies for achieving exotic electronic structures in intermetallic materials.

Catalysis-tunable Heusler alloys in selective hydrogenation of alkynes: A new potential for old materials.

Heusler alloys (X 2 YZ) are well-established intermetallic compound materials in various fields because their function can be precisely adjusted by elemental substitution (e.g., X 2 YZ 1-x Z' x ). Although intermetallic compound catalysts started attracting attention recently, catalysis researchers are not familiar with Heusler alloys. We report their potential as novel catalysts focusing on the selective hydrogenation of alkynes. We found that Co2MnGe and Co2FeGe alloys have great alkene selectivity. Mutual substitution of Mn and Fe (Co2Mn x Fe1-x Ge) enhanced the reaction rate without changing selectivity. The substitution of Ga for Ge decreased the selectivity but increased the reaction rate monotonically with Ga composition. Elucidation of these mechanisms revealed that the fine tuning of catalytic properties is possible in Heusler alloys by separately using ligand and ensemble effects of elemental substitution.

Revealing Electronic Influences in the Semihydrogenation of Acetylene

The electronic influence on the catalytic properties in the semihydrogenation of acetylene is addressed by applying unsupported intermetallic materials from the solid solution Ga1–xSnxPd2 (0 ≤ x ≤ 1). Due to the only marginal changes in the crystal structure, the whole series shows excellent selectivity to ethylene (∼85%) comparable with the binary GaPd2. Moreover, the incremental addition of up to one electron per formula unit reveals a maximum in the specific catalytic activity around the nominal composition with x = 0.28 corresponding to 4.0 atom % tin in the near-surface region, as revealed by operando X-ray photoelectron spectroscopy measurements. The study shows a reliable and quantitative relation between the d-band shift and catalytic activity, revealing once more the potential of intermetallic compounds in heterogeneous catalysis.

Wear-Resistant High-Temperature Composite Slide Bearings Based on Titanium Aluminides

The structure and properties of composite materials have been studied versus their composition. Comparative analysis of intermetallic titanium materials in dry friction with steel has been carried out. The intermetallic titanium material whose structure is represented by an intermetallic matrix with solid-phase inclusions has the highest tribotechnical properties.

Pathways of phase transformation in β-phase-stabilized σ/γ-TiAl alloys subjected to two-step heat treatments

In order to increase the maximum service temperature of intermetallic TiAl materials novel alloy and microstructure concepts are required. Thus, this study focuses on so-called σ/γ-TiAl materials alloyed with β-stabilizing elements Cr and Mo. These alloys in principle show improved mechanical capabilities, but their microstructure control necessitates judicious design of composition and heat treatment parameters. In this work the effects of the alloying elements Cr and Mo are elucidated. The presence of these elements retards the formation of γ- and σ-phases due to diffusional redistribution required, thereby, allowing for the formation of a fine-grained matrix with an embedded particle structure.

Synthesis of alumina ceramic encapsulation for self-healing materials on thermal barrier coating

Durability of Thermal Barrier Coating or TBC can be optimized by inducing Self-Healing capabilities with intermetallic materials MoSi2. Nevertheless, high temperature operation causes the self-healing materials to become oxidized and lose its healing capabilities. Therefore, a method to introduce ceramic encapsulation for MoSi2 is needed to protect it from early oxidation. The encapsulation process is synthesized through a simple precipitation method with colloidal aluminum hydroxide as precursor and variations on calcination process. Semi-quantitative analysis on the synthesized sample is done by using X-ray diffraction (XRD) method. Meanwhile, qualitative analysis on the morphology of the encapsulation was carried out by using Scanning Electron Microscope (SEM) and Field Emission Scanning Electron Microscope (FESEM) equipped with dual Focus Ion Beam (FIB). The result of the experiment shows that calcination process significantly affects the final characteristic of encapsulation. The optimum encapsulation process was synthesized by colloidal aluminum hydroxide as a precursor, with a double step calcination process in low pressure until 900 °C.

Переменные параметры «упругости» нелинейно деформируемой трансверсально-изотропной среды

Composite materials based on metal and ceramic matrices appear in the design of parts and structures. The mechanical properties of the constituents of these com-posite materials are comparable. The design of parts made of polymer composite materials is usually based on the assumption of elastic deformations of constituents of the composite material, including the polymer matrix. This assumption does not always work for metal and ceramic composite materials, which makes it difficult to optimize products made of such materials. In addition, the assumption of the elas-ticity of the composites makes it impossible to estimate the ultimate deformation of the parts. In this connection, nonlinear properties of inhomogeneous, transversally anisotropic composite materials based on metallic or intermetallic matrices are dis-cussed here. It is assumed that the nonlinear properties of composite materials are formed by the nonlinear behavior of the matrix. Earlier, on the basis of the modi-fied theory of plastic flow, nonlinear dependences of the deformation of an anisot-ropic matrix were obtained. The modified theory of plastic flow makes it possible to take into account the nonlinear dependence not only between deviators of stresses and deformations, but also between the first invariants of stresses and de-formations. The nonlinearity in the dependence of the first invariants can be caused by particular manufacturing technology. Five independent strain curves for unidi-rectionally reinforced composite materials were obtained using the Maxwell and Feucht models. The obtained relations are used to find the stress-strain curves of an aluminum alloy unidirectionally reinforced with boron fibers.

Structural, electronic and thermoelectric properties of the intermetallic materials based on Mg2X (X= Si, Ge, Sn): DFT calculations

The scope of this work is the investigation of the physical properties of chalcopyrite materials using ab-initio methods in order to simulate a new structure of thin-films photovoltaic cells with high conversion efficiency. In the first framework, we obtained the results of calculations based on Density Functional Theory (DFT) using the full-potential linearized augmented plane wave method (FP-LAPW) as involved in the WIEN2K computational package. For the exchange-correlation potential, the local density approximation (LDA) was used to calculate the lattice parameters, Bulk modulus and its first derivative as well as the densities of states of the intermetallic semiconductors materials based on Mg2X (X=Si, Ge and Sn). The semi-local Becke-Johnson (mBJ) potential and its modified form proposed by Tran and Blaha (TB-mBJ) were also used for studying the electronic and thermoelectric properties; (merit factor, Seebeck coefficient, electronic conductivity). The achieved results were compared to computational works and other data acquired experimentally.

Investigation of Mechanical Properties of Fe-Doped Intermetallic NiAl

Last few decades intermetallic materials such as NiAl are mechanical and physical properties for high temperature practice. Especially high melting point, excellent oxidation resistance and high hardness properties draw the attention in that intermetallics. It is known that Ni-Al intermetallics are commonly used in various application fields with the addition of Fe, in particular as well as elements such as Ti, Cr, Mo and Co which are related to this group for improving properties thereof. It is especially determined that Fe additive provides positive results in terms of moderate intensity, high strenght and corrosion resistance in the produced intermetallics. Sintering process was used in this work, NiAl powder mixture and Fe powder were sintered at different temperatures. Scanning electron microscopy imaging, EDX line analysis tests performed respectively to sintering samples.

Fabrication of Functionally Graded Ti and γ-TiAl by Laser Metal Deposition

TiAl alloys have become a popular choice in the aerospace and automotive industries, owing to their high specific yield strength, specific modulus, and oxidation resistance over titanium alloys and Ni-based super alloys at elevated temperatures. Although laser metal deposition (LMD) techniques have been available for manufacturing metal alloys for a decade, limited research has been focused on joining intermetallic materials with dissimilar materials using LMD. Here, LMD was used to join titanium aluminide Ti-48Al-2Cr-2Nb and commercially pure titanium with an innovative transition path. The theorized transition was implemented by fabricating functionally graded material (FGM). Porosity- and crack-free deposits were successfully fabricated. Energy dispersive x-ray spectroscopy analysis revealed the final composition was very close to the design composition. X-ray diffraction showed the expected phases were formed. The Vickers hardness, ultimate tensile strength, and coefficient of thermal expansion were evaluated to characterize the FGM’s mechanical and physical properties. The properties of the material were comparable to those of as-cast material as reported in the literature .

Largest Magnetic Moments in the Half-Heusler Alloys XCrZ (X = Li, K, Rb, Cs; Z = S, Se, Te): A First-Principles Study.

A recent theoretical work indicates that intermetallic materials LiMnZ (Z = N, P) with a half-Heusler structure exhibit half-metallic (HM) behaviors at their strained lattice constants, and the magnetic moments of these alloys are expected to reach as high as 5 μB per formula unit. (Damewood et al. Phys. Rev. B 2015, 91, 064409). This work inspired us to find new Heusler-based half-metals with the largest magnetic moment. With the help of the first-principles calculation, we reveal that XCrZ (X = K, Rb, Cs; Z = S, Se, Te) alloys show a robust, half-metallic nature with a large magnetic moment of 5 μB at their equilibrium and strained lattice constants in their most stable phases, while the excellent HM nature of LiCrZ (Z = S, Se, Te) alloys can be observed in one of their metastable phases. Moreover, the effects of uniform strain in LiCrZ (Z = S, Se, Te) alloys in type II arrangement have also been discussed.

Effect of Surface Topography on Room Temperature Tensile Ductility of TiAl

Room temperature tensile ductility of extruded Ti-47Al-1.5Nb-1Cr-1Mn-0.5B (at.%) with different surface topographies was investigated. Tensile specimens were subjected to grinding with sandpaper of different grits and electrolytic polishing to achieve different surface topographies. Surface morphology/topography and tensile ductility of different surface preparations were compared. Results show that for ground samples, when the mean amplitude deviation (Ra) exceeds 0.1 mu m, initiation of tensile failure transits from the sample interior to surface, and tensile fracture strain decreases linearly with increasing Ra. Electrolytic polishing improves the surface topography of TiAl not only by reducing Ra, but also by modifying the amplitude shape and distribution of the surface, and it therefore increases ductility. The present work suggests that surface amplitude deviation (Ra), skewness (Rsk) and kurtosis (Rku) are appropriate parameters to evaluate the surface topography of intermetallic materials with limited ductility such as TiAl.