Cu8GeSe6–Ag8GeS6 System: Phase Equilibria and High-Entropy Alloys

Single crystal preparation and properties of the AgGaGeS4–AgGaGe3Se8 solid solution

The phase equilibria of the Sb2Te2S-Bi2Te2S system was studied by powder X-ray diffraction (PXRD), differential thermal analysis (DTA), scanning electron microscope (SEM) and energy dispersive Xray (EDX) microanalysis. It was shown that due to incongruent melting of the Sb2Te2S compound the system is non-quasibinary, but it is stable below the solidus and characterized by the formation of a continuous series of solid solutions with a tetradymite-like hexagonal structure. The lattice parameters were determined from powder diffraction patterns. It was established that the crystal lattice parameters of solid solutions vary linearly with composition

Phase equilibria in the Tl5Te3–Tl9BiTe6–Tl9TbTe6 system have been studied using differential thermal analysis, X-ray diffraction, and microhardness measurements. We have mapped out a number of vertical sections, the 760-K isothermal section of its phase diagram, and projections of its liquidus and solidus surfaces. The composition dependences of lattice parameters and microhardness have been obtained. The system has been shown to contain a continuous series of solid solutions, which crystallize in a tetragonal structure (Tl5Te3 type, sp. gr. I4/mcm).

1. The systems, potassium permanganate-potassium perchlorate-water and ammonium chloride-manganous chloride-water, have been studied at equilibrium conditions by phase rule and x-ray diffraction methods. 2. The system potassium permanganate-potassium perchlorate-water yields a continuous series of solid solutions having orthorhombic crystal symmetry. For these, the components of which are of similar crystal and chemical structure and of identical valence type, Vegard's additivity law is followed by the a0 and c0 lattice constants, but the b0 constant shows a definite deviation. 3. A method is described of obtaining homogeneous crystals with a particle size which gives excellent powder diffraction photograms in cases where heat annealing is not feasible. 4. A method of analyzing for ClO4— is given. 5. The danger of making serious errors is pointed out in the use of rapid precipitation by chemical reaction or from supersaturated solutions as a method of preparing solid solutions for the study of the relationship between their lattice constants and composition. 6. The system ammonium chloride-manganous chloride-water shows three solid solution series; the crystals obtained in the first series have cubic symmetry, while in the others the symmetry is tetragonal. 7. The mechanism of the formation of the ``anomalous'' solid solutions between ammonium chloride and manganous chloride is given. Experimental and other considerations verify it. 8. It is shown that Vegard's law is not followed by the first solid solution series in which the components are of dissimilar chemical and crystal structure and dissimilar valence types. The curve for the relationship between the lattice constants and composition rises to a maximum and then falls off. Reasons to explain why this law does not apply to these solid solutions are given. 9. The existence of a new ``compound,'' 6NH4Cl·MnCl2·2H2O, is demonstrated. This and the known compound, 2NH4Cl·MnCl2·-2H2O, are considered to be examples of ``compounds of variable composition.'' They are tetragonal with a0 = 15.256±0.004A, c0 = 16.008±0.007A and a0 = 7.5139±0.0005A, c0 = 8.245±0.003A, respectively. The structure of the latter is that of 2NH4Cl·CuCl2·2H2O which belongs to space group D414h or P4mnm.

In this work, the evolution of the structure and phase composition of the multicomponent Ni-Fe-Cr-W-Mo system during mechanical alloying (MA) of an equiatomic mixture of elemental metal powders in a planetary mill is investigated. The formation of the phase composition and structure of the powdered equiatomic high-entropy NiFeCrWMo alloy at different stages of mechanical alloying was determined by scanning electron microscopy, X-ray diffraction and X-ray spectral analysis. It was found that during 10 hours of МА, a single-phase high-entropy alloy with the structure of a BCC solid solution in the nanostructural state with a crystallite size of 22 nm and a lattice strain (microstress) of 0.61 % was formed. It was shown that the metal components were completely dissolved in the solid state during mechanical alloying, in contrast to their limited solubility under equilibrium conditions. Moreover, despite the different features of the formation of solid solutions in high-entropy alloys and traditional materials, the order of dissolution of element atoms in the lattice of a solid solution follows general principles and occurs depending on the melting point in the following sequence: Ni→Fe→Cr→Mo→W. The average particle size of the produced powdered NiFeCrWMo high-entropy alloy is 3.8 μm, and their shape is predominantly spherical or close to spherical. The microstructure of the particles of the powdered NiFeCrWMo high-entropy alloy at the early stage (1.5 hours) of mechanical alloying is a layered structure formed in the process of grinding, deformation, and cold welding of particles of elemental metal powders. After 10 hours of МА, the microstructure of the alloy particles becomes homogeneous and contains a small amount of WC inclusions as a result of milling due to wear of grinding bodies in the MА process. The obtained NiFeCrWMo high-entropy alloy can be used in the future as a component/binder for other composite materials, for example, hard alloys based on WC to replace Co. Keywords: high-entropy alloy, mechanical alloying, structure, phase composition, solid solution, nanostructure

Alloys of the Hf-Rh-Ir system are refractory materials similar to Ni-based superalloys with higher melting temperatures, low values of thermal expansion coefficients, good mechanical properties at high temperatures and oxidation resistance. Binary alloys based on HfRh3 or HfIr3 are proposed as thermal barrier coatings, on Hf2Rh — as hydrogen adsorbents. To develop high-temperature functional materials based on the Hf-Rh-Ir alloys, an understanding of phase equilibria in this system is essential. The alloys of the Hf-Rh-Ir system of 16 compositions are prepared from iodide processed Hf, Rh wire and refined Ir powder (purity of 99.98%, 99.97% and 99.97%, respectively) by arc melting. The alloys are investigated in as-cast and annealed at subsolidus temperatures states by optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis, melting points measurements (Pirani-Alterthum technique) and X-ray diffraction. Based on the results of the alloys studies, solidus surface of the Hf-Rh-Ir system [1] as well as liquidus surface, melting diagram and Scheil diagram are represented. Also the vertical temperature-composition sections of the system phase diagram by the ray Ir : Rh = 1 : 1, along the isopleths at 15,0 at.% Ir, 10,0 and 42,5 at.% Rh as well as at 30,0; 33,0 and 62,5 at.% Hf are constructed for the first time. These sections demonstrate characteristic peculiarities of phase equilibria in the system in particular temperature ranges of alloys crystallization and character of phase transformations. So, the vertical section by the ray Ir : Rh = 1 : 1 shows the influence of Hf on the phase equilibria character. It was established that liquidus and solidus curves of the continuous series of solid solutions between high-temperature modifications of HfRh and HfIr with CsCl-type structure decrease quite steeply (vertical sections by the ray Ir : Rh = 1 : 1 and along the isopleths at 15,0 at.% Ir and 10,0 at.% Rh).

Photo-induced charge-transfer phase transition of rubidium manganese hexacyanoferrate in ferromagnetic and paramagnetic states

The Al–Ni–Si phase diagram. Part II: phase equilibria between 33.3 and 66.7 at.% Ni

The method of improving the microstructure and thus the properties of alloys by adjusting their composition has been widely used in the study of high entropy alloys (HEAs). However, most studies have focused on improving the properties of HEAs with face-centered cubic (FCC) or body-centered cubic (BCC) structures by adjusting the contents of elements such as Ni, Al, Ti, Cr, Mn and Mo. The doping of B, Mg and Zr also has a certain effect on the mechanical properties of HEAs. In this paper, the phase structure, microstructure, and mechanical properties of Ni45.5Co22Fe22Al5Ti5 HEA doped with B, Mg, and Zr were investigated. The results demonstrated that the three-phase structures of FCC matrix, L12 precipitate, and BCC phase were present in all the as-cast HEAs of Ni45.5Co22Fe22Al5Ti5×0.5 (X = B, Mg, and Zr). The microstructures of the as-cast alloys showed typical dendritic and inter-dendritic architecture. The maximum hardness was found in the alloy doped with B element, with a value of 433 HV. During the compressive test at room temperature, neither the Mg0.5 HEA nor the Zr0.5 HEA cracked until the load limit, but the B0.5 HEA cracked at a compressive strain of about 12%. B0.5 HEA had the highest compressive yield strength of the three alloys, followed by Zr0.5 HEA, while Mg0.5 HEA had the lowest, with values of 1030 MPa, 754 MPa, and 628 MPa, respectively. The work is expected to provide a boost for the research on the optimization of the properties of new HEAs reinforced by precipitation of L12 phase by providing a simple solution-microalloying method.

CoCrFeNiX (X=Mn, Cu) high entropy alloys (HEAs) were prepared by powder metallurgy. The effects of milling time and milling speed on the microstructures and properties of CoCrFeNiX (X=Mn, Cu) HEAs were studied. The results show that at high rotational speed, the particle size of the HEA powders is refined and is tended to be uniform, and obvious solid solution phenomenon occurs; the microstructure of CoCrFeNiMn HEA is mainly composed of BCC solid solution, FCC solid solution and CoNiCr intermetallic compound; with the increase of ball milling time, Cr-rich phase and CoNiCr compound decrease. The microstructure of CoCrFeNiCu HEA is mainly composed of BCC solid solution and FCC solid solution; with the increase of ball milling time, Ni-rich FCC solid solution is gradually replaced by Co-rich and Ni-rich FCC solid solution. CoCrFeNiMn and CoCrFeNiCu HEAs have higher compressive strength, compression ratio and hardness, and they are 1300 Mpa and 1100 Mpa, 34% and 33%, 400 HV and 350 HV, respectively; The friction coefficient curve of CoCrFeNiMn HEA is more stable than that of CoCrFeNiCu HEA.

In this study the effect of three different nickel concentration on the microstructure, hardness and corrosion properties of high entropy alloys (HEAs) from AlCrFeCoNi system as an alternative material for medical instruments fabrication was investigated. The analyzed HEAs were AlCrFeCoNix obtained by vacuum arc remelting from high purity raw materials and having nickel atomic ratio x = 1.0, 1.4 and 1.8. The microscopy examination revealed the dendritic morphology for the reference alloy (AlCrFeCoNi) and that the extent of the interdendritic areas increased with the concentration of nickel while Cr was more segregated in the interdendritic areas than in dendrites. Hardness values decreased as the percentage of nickel increased due to the dissolution of the precipitates in a nickel-rich matrix and consequently the formation of continuous solid solutions. The corrosion properties of the synthesized HEAs were evaluated using a potentiodynamic polarization method. The alloys were immersed in Simulated Body Fluid during one week and the corrosion parameters were recorded. The low corrosion rates, low corrosion currents and high polarization resistance attest the good stability of these HEAs in simulated biological environment indicating their possible use for surgical and dental instruments.

STRUCTURE OF ISOTHERMAL SECTIONS OF THE DIAGRAM OF THE STATE OF THE SYSTEM ZrO2 – La2O3 – Eu2O3 AT TEMPERATURES 1500 AND 1250 °C

A Raman study of both phases of barium metaborate (BBO)

Insights on phase formation from thermodynamic calculations and machine learning of 2436 experimentally measured high entropy alloys

To improve the wear properties of AZ91D magnesium alloys, a AlFeCuCoNiCrTi1.5high entropy alloy (HEA) coating was fabricated on AZ91D magnesium alloys by laser cladding using mixed powders of Al, Fe, Cu, Co, Ni, Cr, and Ti. The microstructure of the HEA coating was characterized by OM, SEM, and XRD. The wear resistance of the HEA coating was evaluated under dry sliding wear test condition at room temperature. The results show that the HEA coating mainly consists of a simple BCC solid solution phase. The HEA coating exhibits excellent wear resistance. The main wear mechanisms of the HEA coating and the AZ91D substrate were different, the former dominated by oxidative abrasive wear and the latter suffered from both adhesive and abrasive wear.