On the Microstructure and Properties of Nb-Ti-Cr-Al-B-Si-X (X = Hf,Sn, Ta) Refractory Complex Concentrated Alloys

We studied the effect of the addition of Hf, Sn, or Ta on the density, macrosegregation, microstructure, hardness and oxidation of three refractory metal intermetallic composites based on Nb (RM(Nb)ICs) that were also complex concentrated alloys (i.e., RM(Nb)ICs/RCCAs), namely, the alloys TT5, TT6, and TT7, which had the nominal compositions (at.%) Nb-24Ti-18Si-5Al-5B-5Cr-6Ta, Nb-24Ti-18Si-4Al-6B-5Cr-4Sn and Nb-24Ti-17Si-5Al-6B-5Cr-5Hf, respectively. The alloys were compared with B containing and B free RM(Nb)ICs. The macrosegregation of B, Ti, and Si was reduced with the addition, respectively of Hf, Sn or Ta, Sn or Ta, and Hf or Sn. All three alloys had densities less than 7 g/cm³. The alloy TT6 had the highest specific strength in the as cast and heat-treated conditions, which was also higher than that of RCCAs and refractory metal high entropy alloys (RHEAs). The bcc solid solution Nb_ss and the tetragonal T2 and hexagonal D8₈ silicides were stable in the alloys TT5 and TT7, whereas in TT6 the stable phases were the A15-Nb₃Sn and the T2 and D8₈ silicides. All three alloys did not pest at 800 °C, where only the scale that was formed on TT5 spalled off. At 1200 °C, the scale of TT5 spalled off, but not the scales of TT6 and TT7. Compared with the B free alloys, the synergy of B with Ta was the least effective regarding oxidation at 800 and 1200 °C. Macrosegregation of solutes, the chemical composition of phases, the hardness of the Nb_ss and the alloys, and the oxidation of the alloys at 800 and 1200 °C were considered from the perspective of the Niobium Intermetallic Composite Elaboration (NICE) alloy design methodology. Relationships between properties and the parameters VEC, δ, and Δχ of alloy or phase and between parameters were discussed. The trends of parameters and the location of alloys and phases in parameter maps were in agreement with NICE.     

Influence of Dissolving Fe–Nb–B–Dy Alloys in Zirconium on Phase Structure,Microstructure and Magnetic Properties

This paper refers to the structural and magnetic properties of [(Fe₈₀Nb₆B₁₄)_0.88Dy_0.12]_1−xZr_x (x = 0; 0.01; 0.02; 0.05; 0.1; 0.2; 0.3; 0.5) alloys obtained by the vacuum mold suction casting method. The analysis of the phase contribution indicated a change in the compositions of the alloys. For x < 0.05, occurrence of the dominant Dy₂Fe₁₄B phase was observed, while a further increase in the Zr content led to the increasing contribution of the Fe–Zr compounds and, simultaneously, separation of crystalline Dy. The dilution of (Fe₈₀Nb₆B₁₄)_0.88Dy_0.12 in Zr strongly influenced the magnetization processes of the examined alloys. Generally, with the increasing x parameter, we observed a decrease in coercivity; however, the unexpected increase in magnetic saturation and remanence for x = 0.2 and x = 0.3 was shown and discussed.     

Structure and Mechanical Properties of Cu–Al–Mn Alloys Fabricated by Electron Beam Additive Manufacturing

In this work, the method of electron beam additive manufacturing (EBAM) was used to fabricate a Cu-based alloy possessing a shape memory effect. Electron beam additive technology is especially relevant for copper and its alloys since the process is carried out in a vacuum, which makes it possible to circumvent oxidation. The main purpose of the study was to establish the influence of the printing parameters on the structure of the obtained products, their phase composition, mechanical properties, dry friction behavior, and the structure-phase gradient that formed in Cu–Al–Mn alloy samples during electron beam layer-by-layer printing. The results of the study allowed us to reveal that the structure-phase composition, the mechanical properties, and the tribological performance of the fabricated material are mainly affected by the magnitude of heat input during electron beam additive printing of Cu–Al–Mn alloy. High heat input values led to the formation of the β1′ + α decomposed structure. Low heat input values enabled the suppression of decomposition and the formation of an ordered 1 structure. The microhardness values were distributed on a gradient from 2.0 to 2.75 GPa. Fabricated samples demonstrated different behaviors in friction and wear depending on their composition and structure, with the value of the friction coefficient lying in the range between 0.1 and 0.175.     

Effect of Rare Earth Metals (Y,La) and Refractory Metals (Mo,Ta, Re) to Improve the Mechanical Properties of W–Ni–Fe Alloy—A Review

Tungsten heavy alloys are two-phase metal matrix composites that include W–Ni–Fe and W–Ni–Cu. The significant feature of these alloys is their ability to acquire both strength and ductility. In order to improve the mechanical properties of the basic alloy and to limit or avoid the need for post-processing techniques, other elements are doped with the alloy and performance studies are carried out. This work focuses on the developments through the years in improving the performance of the classical tungsten heavy alloy of W–Ni–Fe through doping of other elements. The influence of the percentage addition of rare earth elements of yttrium, lanthanum, and their oxides and refractory metals such as rhenium, tantalum, and molybdenum on the mechanical properties of the heavy alloy is critically analyzed. Based on the microstructural and property evaluation, the effects of adding the elements at various proportions are discussed. The addition of molybdenum and rhenium to the heavy alloy gives good strength and ductility. The oxides of yttrium, when added in a small quantity, help to reduce the tungsten’s grain size and obtain good tensile and compressive strengths at high temperatures.     

Structure and Superconductivity of Tin-Containing HfTiZrSnM (M = Cu,Fe, Nb,Ni) Medium-Entropy and High-Entropy Alloys

In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)₅Sn₃ partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors.     

Investigation of Thermal Stability of Microstructure and Mechanical Properties of Bimetallic Fine-Grained Wires from Al–0.25%Zr–(Sc,Hf) Alloys

Thermal stability of composite bimetallic wires from five novel microalloyed aluminum alloys with different contents of alloying elements (Zr, Sc, and Hf) is investigated. The alloy workpieces were obtained by induction-casting in a vacuum, preliminary severe plastic deformation, and annealing providing the formation of a uniform microstructure and the nucleation of stabilizing intermetallide Al₃(Zr,Sc,Hf) nanoparticles. The wires of 0.26 mm in diameter were obtained by simultaneous deformation of the Al alloy with Cu shell. The bimetallic wires demonstrated high strength and improved thermal stability. After annealing at 450–500 °C, a uniform fine-grained microstructure formed in the wire (the mean grain sizes in the annealed Al wires are 3–5 μm). An increased hardness and strength due to nucleation of the Al₃(Sc,Hf) particles was observed. A diffusion of Cu from the shell into the surface layers of the Al wire was observed when heating up to 400–450 °C. The Cu diffusion depth into the annealed Al wire surfaces reached 30–40 μm. The maximum elongation to failure of the wires (20–30%) was achieved after annealing at 350 °C. The maximum values of microhardness (H_v = 500–520 MPa) and of ultimate strength (σ_b = 195–235 MPa) after annealing at 500 °C were observed for the wires made from the Al alloys alloyed with 0.05–0.1% Sc.     

Determination of Phase Transition and Critical Behavior of the As-Cast GdGeSi-(X) Type Alloys (Where X = Ni,Nd and Pr)

The aim of the paper is to present a study of the magnetocaloric effect and the nature of phase transition in the Gd₈₀Ge₁₅Si₅ (S1), Gd₇₅Ge₁₅Si₅Ni₅ (S2), Gd₇₅Ge₁₅Si₅Pr₅ (S3) and Gd₇₅Ge₁₅Si₅Nd₅ (S4) alloys. The magnetic entropy changes determined for studied samples, under external magnetic field ~3T, were 11.91, 12.11, 5.08 and 4.71 J/(kg K) for S1, S2, S3 and S4, respectively. The values of refrigerant capacity (under ~3T) were 164, 140, 160 and 140 J/kg for S1, S2, S3 and S4, respectively. The first order phase transition was detected for samples S1 and S2, while specimens S3 and S4 manifested the second order phase transition at the Curie point (T_C). The analysis of temperature evolution of the exponent n (ΔS_M = C·(B_max)ⁿ) showed the validity of this method in detecting either the first or the second order phase transition and the structural transition. The analysis of critical behavior was carried out for samples S3 and S4. The critical exponents and precise T_C values were calculated. The ascertained critical exponents were used to determine the theoretical value of the exponent n, which corresponded well with experimental result.     

Influence of Molybdenum on the Microstructure,Mechanical Properties and Corrosion Resistance of Ti20Ta20Nb20(ZrHf)20−xMox (Where: x = 0, 5, 10, 15, 20) High Entropy Alloys

The presented work was focused on investigating the influence of the (hafnium and zirconium)/molybdenum ratio on the microstructure and properties of Ti₂₀Ta₂₀Nb₂₀(ZrHf)_20−xMo_x (where: x = 0, 5, 10, 15, 20 at.%) high entropy alloys in an as-cast state. The designed chemical composition was chosen due to possible future biomedical applications. Materials were obtained from elemental powders by vacuum arc melting technique. Phase analysis revealed the presence of dual body-centered cubic phases. X-ray diffraction showed the decrease of lattice parameters of both phases with increasing molybdenum concentration up to 10% of molybdenum and further increase of lattice parameters. The presence of two-phase matrix microstructure and hafnium and zirconium precipitates was proved by scanning and transmission electron microscopy observation. Mechanical property measurements revealed decreased micro- and nanohardness and reduced Young’s modulus up to 10% of Mo content, and further increased up to 20% of molybdenum addition. Additionally, corrosion resistance measurements in Ringers’ solution confirmed the high biomedical ability of studied alloys due to the presence of stable oxide layers.     

First-Principles Study of Mechanical and Thermodynamic Properties of Binary and Ternary CoX (X = W and Mo) Intermetallic Compounds

In this study, the structural, elastic, and thermodynamic properties of DO₁₉ and L1₂ structured Co₃X (X = W, Mo or both W and Mo) and μ structured Co₇X₆ were investigated using the density functional theory implemented in the pseudo-potential plane wave. The obtained lattice constants were observed to be in good agreement with the available experimental data. With respect to the calculated mechanical properties and Poisson’s ratio, the DO₁₉-Co₃X, L1₂-Co₃X, and μ-Co₇X₆ compounds were noted to be mechanically stable and possessed an optimal ductile behavior; however, L1₂-Co₃X exhibited higher strength and brittleness than DO₁₉-Co₃X. Moreover, the quasi-harmonic Debye–Grüneisen approach was confirmed to be valid in describing the temperature-dependent thermodynamic properties of the Co₃X and Co₇X₆ compounds, including heat capacity, vibrational entropy, and Gibbs free energy. Based on the calculated Gibbs free energy of DO_19-Co₃X and L1₂-Co₇X₆, the phase transformation temperatures for DO_19-Co₃X to L1₂-Co₇X₆ were determined and obtained values were noted to match well with the experiment results.     

Fabrication,Structure, and Thermal Properties of Mg–Cu Alloys as High Temperature PCM for Thermal Energy Storage

This work studied the thermophysical properties of Mg-24%Cu, Mg-31%Cu, and Mg-45%Cu (wt.%) alloys to comprehensively consider the possibility of using them as thermal energy storage (TES) phase change materials (PCMs) used at high temperatures. The microstructure, phase composition, phase change temperatures, and enthalpy of these alloys were investigated by an electron probe micro analyzer (EPMA), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The XRD and EPMA results indicated that the binary eutectic phase composed of α-Mg and Mg₂Cu exists in the microstructure of the prepared Mg–Cu series alloys. The microstructure of Mg-24%Cu and Mg-31%Cu is composed of α-Mg matrix and binary eutectic phases, and Mg-45%Cu is composed of primary Mg₂Cu and binary eutectic phases. The number of eutectic phases is largest in Mg-31%Cu alloy. The DSC curves indicated that the onset melting temperature of Mg-24%Cu, Mg-31%Cu, and Mg-45%Cu alloys were 485, 486, and 485 °C, and the melting enthalpies were 152, 215, and 91 J/g. Thermal expansion and thermal conductivity were also determined, revealing that the Mg–Cu alloys had a low linear thermal expansion coefficient and high thermal conductivity with respect to increasing temperatures. In conclusion, the thermal properties demonstrated that the Mg–Cu alloys can be considered as a potential PCM for TES.     

The Effects of La Doping on the Crystal Structure and Magnetic Properties of Ni2In-Type MnCoGe1−xLax (x = 0, 0.01, 0.03) Alloys

In this experiment, a series of MnCoGe_1−xLa_x (x = 0, 0.01, 0.03) alloy samples were prepared using a vacuum arc melting method. The crystal structure and magnetic properties of alloys were investigated using X-ray diffraction (XRD), Rietveld method, physical property measurement system (PPMS), and vibrating sample magnetometer (VSM) analyses. The results show that all samples were of high-temperature Ni₂In-type phases, belonging to space group P6₃/mmc (194) after 1373 K annealing. The results of Rietveld refinement revealed that the lattice constant and the volume of MnCoGe_1−xLa_x increased along with the values of La constants. The magnetic measurement results show that the Curie temperatures (T_C) of the MnCoGe_1−xLa_x series alloys were 294, 281, and 278 K, respectively. The maximum magnetic entropy changes at 1.5T were 1.64, 1.53, and 1.56 J·kg⁻¹·K⁻¹, respectively. The respective refrigeration capacities (RC) were 60.68, 59.28, and 57.72J·kg⁻¹, with a slight decrease along the series. The experimental results show that the doping of La results in decreased T_C, basically unchanged magnetic entropy, and slightly decreased RC.     

Tuning of the Structure and Magnetocaloric Effect of Mn1−xZrxCoGe Alloys (Where x = 0.03, 0.05, 0.07, and 0.1)

The aim of the present work is to study the influence of a partial substitution of Mn by Zr in MnCoGe alloys. The X-ray diffraction (XRD) studies revealed a coexistence of the orthorhombic TiNiSi-type and hexagonal Ni₂In- type phases. The Rietveld analysis showed that the changes in lattice constants and content of recognized phases depended on the Zr addition. The occurrence of structural transformation was detected. This transformation was confirmed by analysis of the temperature dependence of exponent n given in the relation ΔS_M = C·(B_MAX)ⁿ. A decrease of the Curie temperature with an increase of the Zr content in the alloy composition was detected. The magnetic entropy changes were 6.93, 13.42, 3.96, and 2.94 J/(kg K) for Mn_0.97Zr_0.03CoGe, Mn_0.95Zr_0.05CoGe, Mn_0.93Zr_0.07CoGe, and Mn_0.9Zr_0.1CoGe, respectively. A significant rise in the magnetic entropy change for samples doped by Zr (x = 0.05) was caused by structural transformation.     

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: III. Matrix and Phases of the High-Coercivity State

Observations of the surface domain structure (Kerr-effect), optical metallography, scanning electron microscopy (SEM-SE), and electron microprobe analysis (EPMA-SEM), measurements of major and minor magnetic hysteretic loops were used to study pseudo-single-crystal samples of (Sm,Zr)(Co,Cu,Fe)_z alloys subjected to heat treatments to the high-coercivity state, which are used in fabricating sintered permanent magnets. Correlations between the chemical composition, hysteretic properties, structural components, domain structure, and phase state were determined for the concentration ranges that ensure wide variations of 4f-/4d-/3d-element ratio in the studied samples. The phase state formed by collinear and coherent phase components determines the high coercive force and ultimate magnetic hysteresis loops of the pseudo-single crystals. It was found that the 1:5 phase with the hexagonal structure (P6/mmm) is the matrix of the alloys for (Sm,Zr)(Co,Cu,Fe)_z permanent magnets; the matrix undergoes phase transformations in the course of all heat treatments for the high-coercivity state. The heterogeneity observed with optical magnifications, namely, the observation of main structural components A and B, is due to the alternation, within the common matrix, of regions with modulated quasi-spherical precipitates and regions with hexagonal bipyramids (cellular phase) although, traditionally, many investigators consider the cellular phase as the matrix. It is shown that the relationship of volume fractions of structural components A and B that account for more than 0.9 volume fraction of the total, which is due to the integral chemical composition of the alloys, determines the main hysteretic performances of the samples. The Zr-rich phases, such as 5:19, 2:7, and 6:23, and a structural component with the variable stoichiometry (Sm(Co,Cu,Fe)_3.5–5) that is almost free of Zr and contains up to 33 at% Cu, were found only within structural component A in quantities sufficient for EPMA analysis.     

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: II. Composition,Magnetization Reversal,and Magnetic Hardening of Main Structural Components

Experimental series of alloys for (Sm,Zr)(Co,Cu,Fe)_Z permanent magnets are presented in the concentration ranges that provide wide variations of (4f)/(4d)/(3d) ratios of comprising elements. Optical metallographic analysis, observation of the surface domain structure upon magnetization reversal (Kerr effect), electron microprobe analysis, and measuring the major hysteresis loops of samples at different stages of heat treatment are used to study processes related to the development of the highly coercive state of these samples. It was found that the volume fractions of two main structural components A and B, which comprise 90% of the total sample volume, rigorously control the coercivity at all stages of thermal aging. At the same time, structural components A and B themselves in samples being in the high-coercivity state differ qualitatively and quantitatively in the chemical composition, domain structure and its development in external magnetic fields and, therefore, are characterized by different morphologies of the phases comprising the structural components. Two stages of phase transformations in the sample structure are observed. During isothermal annealing, the cellular structure develops within the B component, whereas, during stepwise (slow) cooling or quenching from the isothermal aging temperature to 400 °C, a phase structure evolves within both the cell boundaries in B and the structural component A. The degree of completion of the phase transformations within micro- and nano-volumes of the components determines the ultimate hysteretic characteristics of the material.     

Hydrothermal Synthesis of Nanocrystalline ZrO2-8Y2O3-xLn2O3 Powders (Ln = La,Gd, Nd,Sm): Crystalline Structure,Thermal and Dielectric Properties

Zirconium dioxide (ZrO₂) is one of the ceramic materials with high potential in many areas of modern technologies. ZrO₂ doped with 8 wt.% (~4.5 mol%) Y₂O₃ is a commercial powder used for obtaining stabilized zirconia materials (8 wt.% YSZ) with high temperature resistance and good ionic conductivity. During recent years it was reported the co-doping with multiple rare earth elements has a significant influence on the thermal, mechanical and ionic conductivity of zirconia, due complex grain size segregation and enhanced oxygen vacancies mobility. Different methods have been proposed to synthesize these materials. Here, we present the hydrothermal synthesis of 8 wt.% (~4.5 mol%) YSZ co-doped with 4, 6 and 8 wt.% La₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃ respectively. The crystalline phases formed during their thermal treatment in a large temperature range were analyzed by X-ray diffraction. The evolution of phase composition vs. thermal treatment temperatures shows as a major trend the formation at temperatures >1000 °C of a cubic solid solutions enriched in the rare earth oxide used for co-doping as major phase. The first results on the thermal conductivities and impedance measurements on sintered pellets obtained from powders co-doped with 8 wt.% Y and 6% Ln (Ln = La, Nd, Sm and Gd) and the corresponding activation energies are presented and discussed. The lowest thermal conductivity was obtained for La co-doped 8 wt.% YSZ while the lowest activation energy for ionic conduction for Gd co-doped 8 wt.% YSZ materials.     

The Effect of (Mg,Zn)12Ce Phase Content on the Microstructure and the Mechanical Properties of Mg–Zn–Ce–Zr Alloy

The quantitative study of rare earth compounds is important for the improvement of existing magnesium alloy systems and the design of new magnesium alloys. In this paper, the effective separation of matrix and compound in Mg–Zn–Ce–Zr alloy was achieved by a low-temperature chemical phase separation technique. The mass fraction of the (Mg, Zn)₁₂Ce compound was determined and the effect of the (Mg, Zn)₁₂Ce phase content on the heat deformation organization and properties was investigated. The results show that the Mg–Zn–Ce compound in both the as-cast and the homogeneous alloys is (Mg, Zn)₁₂Ce. (Mg, Zn)₁₂Ce phase formation depends on the content and the ratio of Zn and Ce elements in the initial residual melt of the eutectic reaction. The Zn/Ce mass ratios below 2.5 give the highest compound contents for different Zn contents, 5.262 wt.% and 7.040 wt.%, respectively. The increase in the amount of the (Mg, Zn)₁₂Ce phase can significantly reduce the critical conditions for dynamic recrystallization formation. Both the critical strain and the stress decrease with increasing rare earth content. The reduction of the critical conditions and the particle-promoted nucleation mechanism work together to increase the amount of dynamic recrystallization. In addition, it was found that alloys with 6 wt.% Zn elements tend to undergo a dynamic recrystallization softening mechanism, while alloys with 3 wt.% Zn elements tend to undergo a dynamic reversion softening mechanism.     

Structural,Optical, Charge-Transport,and Dielectric Properties of Double-Perovskite La2Co1−zFezMnO6 (z = 0, 0.2–1.0)

A series of double-perovskite La₂Co_1−zFe_zMnO₆ (z = 0, 0.2–1.0) ceramics were synthesized using a well-established sol–gel method. The series of samples with a monoclinic phase and a P2₁/n symmetry were characterized by XRD, FTIR, conductivity, and capacitance measurement to extract charge-transport and dielectric characteristics at room temperature. The obtained IR spectra fitted well with the Lorentz oscillator model to calculate the damping factor, optical frequency, and oscillator strength and compared with the theory, which gave better agreement. The calculated activation energies from the Arrhenius plot supported the semiconducting nature of all samples. The temperature and frequency-dependent dielectric parameters, such as the real part (εr′), imaginary part (ε″) of the dielectric constant, dielectric loss (tanδ), and ac-conductivity (σ_ac) were extracted. The dielectric constant (εr′, ε″) and dielectric loss (tanδ) were enhanced at a low frequency, while the ac-conductivity (σ_ac) displayed higher values at higher frequencies. The enhancement in the dielectric parameters with increasing iron concentrations arose due to the higher surface volume fraction of iron (Fe³⁺) ions than the cobalt (Co³⁺) ions. The radius of the Fe³⁺ (0.645 Å) was relatively higher than the Co³⁺ ions (0.61 Å), significantly influenced by the grains and grain boundaries, and enhanced the barrier for charge mobility at the grain boundaries that play a vital role in space charge polarization.     

First-Principles Study on Possible Half-Metallic Ferrimagnetism in Double Perovskites Pb2XX′O6 (X = Ti,Zr, Hf,V, Nb and Ta,X′ = Tc,Ru, Os and Rh)

Pb-based double perovskite compounds with chemical formula Phey have abundant physical properties in the spintronic field. Among all the features, the spin interaction of half-metallic (HM) is regarded as an important performance measure because of its high potential in spintronic devices. In this research study, we calculate density of state (DOS) to investigate possible half-metal candidates by executing structural optimization based on the method of generalized gradient approximation (GGA) and strong correlation effect (GGA + U). Furthermore, following the earlier methods by calculating and comparing energy difference of various compounds with the four initial magnetic states: ferromagnetic, ferrimagnetic, antiferromagnetic and nonmagnetic, we can determine which magnetic state is more stable. Results indicate that there are 13 possible ferrimagnetic HM candidates in these combinations, including Pb₂NbTcO₆, Pb₂TaTcO₆, Pb₂TiRuO₆, Pb₂ZrRuO₆, Pb₂HfRuO₆, Pb₂VRuO₆, Pb₂NbRuO₆, Pb₂TadRuO₆, Pb₂ZrOsO₆, Pb₂HfOsO₆, Pb₂VOsO₆, Pb₂ZrRhO₆ and Pb₂HfRhO₆ under GGA and GGA + U schemes. The stability of analysis by analyzing the energy gap illustrates that all 13 possible candidates are half metals and ferrimagnetic states, so our studies could provide guidelines for scientists to fabricate new double perovskites in future.     

The Effect of Boron on the Microstructure and Properties of Refractory Metal Intermetallic Composites (RM(Nb)ICs) Based on Nb-24Ti-xSi (x = 16, 17 or 18 at.%) with Additions of Al,Cr or Mo

This paper is about metallic ultra-high temperature materials, in particular, refractory metal intermetallic composites based on Nb, i.e., RM(Nb)ICs, with the addition of boron, which are compared with refractory metal high entropy alloys (RHEAs) or refractory metal complex concentrated alloys (RCCAs). We studied the effect of B addition on the density, macrosegregation, microstructure, hardness and oxidation of four RM(Nb)IC alloys, namely the alloys TT2, TT3, TT4 and TT8 with nominal compositions (at.%) Nb-24Ti-16Si-5Cr-7B, Nb-24Ti-16Si-5Al-7B, Nb-24Ti-18Si-5Al-5Cr-8B and Nb-24Ti-17Si-3.5Al-5Cr-6B-2Mo, respectively. The alloys made it possible to compare the effect of B addition on density, hardness or oxidation with that of Ge or Sn addition. The alloys were made using arc melting and their microstructures were characterised in the as cast and heat-treated conditions. The B macrosegregation was highest in TT8. The macrosegregation of Si or Ti increased with the addition of B and was lowest in TT8. The alloy TT8 had the lowest density of 6.41 g/cm³ and the highest specific strength at room temperature, which was also higher than that of RCCAs and RHEAs. The Nb_ss and T2 silicide were stable in the alloys TT2 and TT3, whereas in TT4 and TT8 the stable phases were the Nb_ss and the T2 and D8₈ silicides. Compared with the Ge or Sn addition in the same reference alloy, the B and Ge addition was the least and most effective at 800 °C (i.e., in the pest regime), when no other RM was present in the alloy. Like Ge or Sn, the B addition in TT2, TT3 and TT4 did not suppress scale spallation at 1200 °C. Only the alloy TT8 did not pest and its scales did not spall off at 800 and 1200 °C. The macrosegregation of Si and Ti, the chemical composition of Nb_ss and T2, the microhardness of Nb_ss and the hardness of alloys, and the oxidation of the alloys at 800 and 1200 °C were also viewed from the perspective of the alloy design methodology NICE and relationships with the alloy or phase parameters VEC, δ and Δχ. The trends of these parameters and the location of alloys and phases in parameter maps were found to be in agreement with NICE.     

Hydrogen Gas Phase and Electrochemical Hydriding of LaNi5−xMx (M = Sn,Co, Al) Alloys

Hydriding/dehydriding properties of a series of LaNi₅ based alloys were compared by applying both hydrogen gas phase and electrochemical hydrogen charge/discharge methods. The highest hydrogen absorption capacity of 1.4 wt.% H₂ was found for LaNi_4.3Co_0.4Al_0.3, although LaNi_4.8Sn_0.2 also reveals comparable hydrogen capacity (>1.3%). A significant difference in the hydriding kinetics was observed for all studied alloys before and after activation. The activated alloys (5 cycles at 65 °C, 40 atm. H₂) reach their maximum capacities after less than a minute, whereas the pure LaNi₅ alloy needs several minutes for complete hydriding. The electrochemical hydriding/dehydriding behavior of the alloys reveals superior performance of LaNi_4.3Co_0.4Al_0.3 and LaNi_4.8Sn_0.2 compared to the other compositions studied, as the capacity of LaNi_4.8Sn_0.2 decreases by only 10% for 60 charge/discharge cycles at a current density of 100 mA/g. Good agreement between the hydrogen sorption kinetics of the alloys obtained electrochemically and from hydrogen gas phase has also been observed.