Decomposition Of Solid Solution Research Articles

Phase transformation and strengthening of the gas-atomized FeCoCrNiMo0.5Al1.3 high-entropy alloy powder during annealing

Phase evolution and strengthening of the FeNiCoCrMo0.5Al1.3 powder alloy produced via inert gas atomization and annealed in the temperature interval of 300–800 °C have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and microhardness testing. It was found that annealing at 300–600 °C leads to an increase of the element segregations between the several solid solutions with a rise of the lattice misfit (ε) to 1.5 % and microhardness growth to 1070 HV. It was assumed that elastic stress caused by the element partitioning is the main strengthening mechanism: microhardness rises linearly with misfit rise with dHV/dε = 43400 MPa. Sigma arises after the maximum elastic deformation (in 1.5 %) was reached. Formation of the dispersed coherent sigma phase in the annealing interval 600–800 °C results in the microhardness rise. Oxidation that began at 800 °C in 27 h is accompanied with FCC formation due to a depletion of the B2 in Al caused by Al2O3 formation. Estimation of the activation energy of the initial stage of the solid solution decomposition gives a very low value in 0.65eV, apparently caused by the high concentration of quenched vacancies. The activation energy of sigma formation approximately coincides with the activation energy of self-diffusion in BCC metals (about 2.60 eV).

Oxidation Behavior of FeNiCoCrMo0.5Al1.3 High-Entropy Alloy Powder.

One of the most promising applications of FeNiCoCrMoAl-based high-entropy alloy is the fabrication of protective coatings. In this work, gas-atomized powder of FeNiCoCrMo0.5Al1.3 composition was deposited via high-velocity oxygen fuel spraying. It was shown that in-flight oxidation of the powder influences the coating's phase composition and properties. Powder oxidation and phase transformations were studied under HVOF deposition, and during continuous heating and prolonged isothermal annealing at 800 °C. Optical and scanning electron microscopy observation, energy dispersive X-ray analysis, X-ray diffraction analysis, thermogravimetric analysis, differential thermal analysis, and microhardness tests were used for study. In a gas-atomized state, the powder consisted of BCC supersaturated solid solution. The high rate of heating and cooling and high oxygen concentration during spraying led to oxidation development prior to decomposition of the supersaturated solid solution. Depleted Al layers of BCC transferred to the FCC phase. An increase in the spraying distance resulted in an increase in α-Al2O3 content; however, higher oxide content does not result in a higher microhardness. In contrast, under annealing, the supersaturated BCC solid solution decomposition occurs earlier than pronounced oxidation, which leads to considerable strengthening to 910 HV.

EFFECT OF EQUAL CHANNEL ANGULAR PRESSING AND SUBSEQUENT AGING ON THE STRUCTURE AND MECHANICAL PROPERTIES OF Al-Mg2Si ALLOYS WITH TRANSITION METAL ADDITIVES

The effect of equal-channel angular pressing (ECAP) at a temperature of 150°C and subsequent aging on the structure and strength characteristics of Al-Mg2Si alloys alloyed with Sc and combined additives (Sc + Zr) and (Sc + Hf) has been studied. An analysis of the dependences of hardness and electrical resistivity on time and temperature revealed the same nature of the decomposition of a supersaturated solid solution of alloys with additives (Sc + Zr) and (Sc + Hf), and also made it possible to obtain optimal aging conditions for these alloys. The microstructure of the alloys and the precipitation of secondary phases were carefully studied using scanning (SEM) and transmission electron microscopy (TEM). In alloys after ECAP and aging, an increase in both strength and ductility was revealed due to the compensation of aging processes by recovery processes associated with the rearrangement of the dislocation structure.

Vliyanie rotatsionnoy kovki na strukturu i svoystva magnievykh splavov sistemy Mg-Y-Gd-Zr

The study results of the structure and mechanical properties of magnesium alloys obtained by rotary forging, similar in composition to the IMB7-1 alloy of the Mg-Y-Gd-Zr system, are presented. Mechanical properties were determined after rotary forging and after rotary forging with subsequent aging at 200 °C for up to 64 hours. The alloys were aged both immediately after rotary forging and after homogenization at 515 °C of the deformed alloys obtained. It is established that rotary forging contributes to the hardening of the studied alloys as a result of grain grinding and intensive twinning. Aging carried out after rotary forging leads to additional hardening of alloys as a result of the decomposition of supersaturated magnesium solid solution. Annealing after rotary forging increases the grain size in the studied alloys due to collective recrystallization and thereby reduces the strength properties of the alloys.

Study of the Al–Sc Solid Solution Decomposition during Annealing of Strained Al–0.5% Mg–Sc Alloys

Study of the Al–Sc Solid Solution Decomposition during Annealing of Strained Al–0.5% Mg–Sc Alloys

Investigation of the Decomposition of Al–Sc Solid Solution during Annealing of Deformed Al–0.5% Mg–Sc Alloys

Abstract—The results of studies of the kinetics of solid solution decomposition during firing of fine-grained conductive alloys Al–0.5% Mg–Sc with different scandium content are presented. The alloys were obtained by induction casting, and the fine-grained microstructure was formed using equal-channel angular pressing. The kinetics of the decomposition of a solid solution has been studied using methods for measuring electrical resistivity and microhardness. The results were analyzed using the Johnson–Mel–Avrami–Kolmogorov equation. It is shown that during the firing of fine-grained alloys, the separation of Al3Sc particles along the nuclei of lattice dislocations is observed, and discontinuous precipitation of scandium in aluminum also occurs.

FORMATION AND DECOMPOSITION OF ANOMALOUS SUPERSATURATED MOLYBDENUM SOLUTIONS IN COPPER-BASED CONDENSATES


 Cu-Mo condensates in the concentration range of the latter from 0.3 to 1.5 at.%, obtained by simultaneous evaporation in vacuum with subsequent condensation of the resulting vapor mixture on a non-orienting substrate (PVD method), were studied. The components of this system do not form chemical compounds under equilibrium conditions and are mutually insoluble in liquid and solid states. The structure of Cu-Mo condensates was studied by transmission electron microscopy and X-ray diffractometry both in the derivative state and after a series of isothermal anneals in the temperature range from 300 to 900°C. It was found that small concentrations of molybdenum lead to significant dispersion of the matrix metal. Molybdenum tends to form segregations at the boundaries of copper grains and form a strong coherent bond with the matrix metal, which persists even after isothermal annealing. The conditions for the formation of an anomalous supersaturated solid solution of molybdenum in the copper matrix, as well as the conditions for its decomposition, have been revealed. An assumption is made about the mechanism of formation of such a solution during condensation from the vapor phase, which consists in the kinetic capture of molybdenum atoms by the crystallization front during condensation from the vapor phase. It was found that the decomposition of the supersaturated solid solution begins when heated to 0.5 of the melting point of copper and is accompanied by a dispersion solidification process. During the experiment, it was first recorded that the dispersion solidification process can have a two-stage character. The first peak is observed in the region of 30 minutes of annealing, and the second peak is observed after about 2 hours of isothermal annealing. The height of the dispersion hardening peaks increases with increasing molybdenum concentration. It is suggested that the appearance of the second peak of dispersion hardening is associated with the peculiarities of the interaction between copper grains and molybdenum segregations at the grain boundaries. It is shown that the structure after solution decomposition is typically composite. The advantage of this material over conventional dispersively hardening alloys is the fact that in these pseudo-alloys there is no reverse solution of hardening particles at an increase in temperature.

Effect of Samarium on the Properties of Hot-Extruded Mg–Y–Gd–Zr Alloys

The effect of such an additional promising alloying element as samarium on hot-extruded Mg–Y–Gd–Zr alloys is investigated. The microstructure, kinetics of aging during the decomposition of a supersaturated Mg solid solution, and the mechanical properties of the alloys are studied. The differences of the recrystallization processes that occur in hot-extruded alloys with various contents of samarium (0, 1.7, 2.5%) are demonstrated. After hot extrusion, Mg–Y–Gd–Zr and Mg–Y–Gd–Sm–Zr alloys are additionally hardened during aging due to the decomposition of a supersaturated Mg solid solution. At the same time, samarium changes the nature of this hardening. The alloys with samarium are hardened faster, and the maximum hardness is achieved with shorter aging exposures. The mechanical properties of hot-extruded Mg–Y–Gd–Zr alloys with samarium addition are determined at room and elevated up to 300 °C temperatures. The efficiency and expediency of using samarium both as a separate alloying element and as a partial replacement of more expensive rare-earth elements in alloys with yttrium and gadolinium are shown.

Study of supersaturated solid solution decomposition during quenching of sheets from Al-Mg-Si aluminum alloy

This paper presents the results of a study of the stability of a supersaturated solid solution (SSS) of sheets made of thermally hardened aluminum alloy of the Al-Mg-Si system with a small addition of copper (Al-0.6Mg-1.0Si-0.2Cu) under various quenching modes. The samples were subjected to isothermal or continuous quenching with different quenching cooling rates, after which artificial aging was carried out at a temperature of 170°C. From the results of thermodynamic modeling of the equilibrium phase composition of the alloy, it was found that for the temperature range from 300 to 530°C, the presence of the β-phase (Mg2Si) is most likely. With the use of transmission electron microscopy and X-ray spectral microanalysis, it was found that during quenching, the decomposition of SSS leads to the precipitation of undesirable large particles of metastable β-type phases or equilibrium β-phase. The nucleation of the secretions is realized in the form of rod-shaped particles by a heterogeneous mechanism mainly on the surface of the α-phase dispersoids (Al15(Mn,Fe)3Si2), which thus significantly increase the quenching sensitivity of the alloy. The formation of these secretions at a low quenching rate causes, during subsequent aging, a decrease in the proportion and density of formation of strengthening particles of the β" phase, and also leads to an increase in their size and heterogeneity of distribution in the aluminum matrix, which reduces the potential of dispersion hardening during aging and corrosion resistance of the material.

Utilization of industrial wastes in Al2O3‐SiC‐SiO2‐C refractories: Characterization of erosion and corrosion resistance

AbstractIndustrial waste has a high potential for reuse in the production of refractories, which can significantly lower costs. The purpose of the research is to access the role of three types of recycled industrial wastes (ferro‐titanium slag [FTS], ferhro‐chromium slag [FCS], and ferro‐vanadium slag [FVS]) utilized as aggregate in the traditional Al2O3‐SiC‐SiO2‐C refractories (ASSC). Erosion and corrosion resistance characterization was performed to determine whether these industrial waste‐containing ASSC still perform better than traditional ASSC during service. Based on the results, incorporating FVS into the ASSC was not recommended, its corrosion resistance was significantly reduced due to the presence of excessive liquid phase. Nonetheless, FTS and FCS could be added as aggregate to the ASSC without affecting their performance. This necessity of the proper amount of liquid phase in ASSC was highlighted in this research since the parameters could alter its properties. Furthermore, the Ti(C,N) transformed from TiO2 in FTS via carbothermal reduction nitridation could effectively prevent further corrosion, and Cr2O3 derived from the decomposition of (Al,Cr)2O3 solid solution in FCS could play the same role during the corrosion process, both of which may be potential raw materials to be used in refractories.

Highly efficient leaching of aluminum and chromium from aluminum chromium slag using NaOH-NaNO3 binary molten salt

In this study, the NaOH-NaNO3 binary molten salt was proposed as a highly efficient technique to leach aluminum and chromium from aluminum chromium slag (ACS). Various factors, such as roasting temperature, roasting time, mass ratio of NaOH (or NaNO3)/ACS, water leaching temperature and time, were adjusted to investigate their influence on the activation and extraction of aluminum-chromium resources from ACS. Moreover, the roasting activation conditions were optimized by response surface methodology, and the optimal extraction rates of alumina and chromium (88.72% and 95.64%, respectively) were obtained with the roasting temperature of 451 °C, roasting time of 3.9 h, NaOH/ACS mass ratio of 5.39:1, and NaNO3/ACS mass ratio of 0.79:1. Kinetic studies showed that the roasting process was controlled by the diffusion of the product interface. Finally, based on the comprehensive analysis of leaching data and physicochemical properties change of ACS with roasting, the mechanism of NaOH-NaNO3-ACS activation was revealed: NaOH-NaNO3 melted and encapsulated the ACS during the roasting reaction, NaOH provided a strongly alkaline environmental medium, which facilitated the decomposition of NaNO3 into NaNO2 and reactive oxygen species, thus prompting the oxidative decomposition of aluminum-chromium solid solution to form NaAlO2 and Na2CrO4, further improving the leaching rate of aluminum and chromium.

Phase stability and thermal expansion of ZnO solid solutions with 3d transition metal oxides synthesized at high pressure

Phase stability and thermal expansion of rock-salt Me1-xZnxO (Me = Ni2+, Co2+, Fe2+, Mn2+) solid solutions synthesized at high pressures and high temperatures have been studied by synchrotron X-ray diffraction in a wide (0.1 ≤ x ≤ 0.8) concentration range. At ambient pressure rs-Me1-xZnxO solid solutions were found kinetically stable up to 670–1100 K depending on the composition and type of Me2+ cation. Temperature-induced decomposition of the single-phase rock-salt solid solutions lead in most cases to the formation of a mixture of two solid solutions, with cubic and wurtzite structures. Oxidation of the Me2+ cation (Co, Mn) by atmospheric oxygen can result in formation of mixed higher oxides of these metals. In all the systems studied, the rock-salt solid solutions show a linear temperature dependence of the thermal expansion, but for the compositions with the highest ZnO content, deviations from the linear dependence are observed.Received 14.03.2023; revised XX.XX.2023; accepted XX. XX.2023; published XX. XX.2023.

"The resonance between the mixing energy and the elastic strain energy as the reason for the composition modulation effect appearance during the spinodal decomposition of GaInPAs solid solutions "

"The resonance between the mixing energy and the elastic strain energy as the reason for the composition modulation effect appearance during the spinodal decomposition of GaInPAs solid solutions "

Structure evolution and mechanical properties of Al-alloyed tantalum diboride films prepared by magnetron sputtering co-deposition

Alloying of transition metal diborides with other metals seems to be a suitable way to maintain their excellent mechanical properties under high-temperature loads. Here, we focus on the perspective tantalum diboride (TaB2) hard film, where we investigate the effect of aluminum alloying on the thermally induced structural evolution and mechanical properties of α-Ta1−xAlxB2 using a combination of density functional theory and experiments. Ab initio calculations predict a strong tendency toward the spinodal phase decomposition of the α-TaAlB2 solid solution into isostructural binaries in the entire concentration range at T = 0 K. However, an increase in temperature (T > 773 K) leads to stabilization of the α-Ta1−xAlxB2 solid solution at x < 0.5. The experimental results of magnetron co-sputtered Ta0.75Al0.25B2.14 and Ta0.69Al0.31B2.16 films with aluminum concentrations of 8 and 12.5 at. %, respectively, confirm the insolubility of aluminum in the TaB2 phase. The structure has a nanocomposite character formed by α-TaB2 nanofilaments surrounded by an Al-rich tissue phase. The films are structurally stable up to 1200 °C, but Al atoms already begin to diffuse from the boundary regions when the temperature exceeds 1000 °C. Al alloying causes a decrease in hardness, since the hardness of the reference as-deposited TaB1.21, Ta0.75Al0.25B2.14, and Ta0.69Al0.31B2.16 films is 34, 28, and 27 GPa, respectively. Exposing the films to high temperatures does not lead to a hardening effect; the hardness of Al-depleted films annealed at a temperature of 1200 °C decreased by approximately 10%. The decrease in Young's modulus from 420 GPa (TaB1.21) to 370 GPa (Ta0.69Al0.31B2.16) indicates a tendency toward the ductile behavior of Al alloyed films under mechanical load.

Enhancement in dispersoid precipitation and dispersion strengthening by prior deformation in an Al–Mg–Mn alloy

Dispersion strengthening effect of Mn-containing dispersoids in the non-age hardenable Al–Mg–Mn alloys is generally limited since it is difficult to achieve the high-density and fine sized dispersoids through conventional homogenization treatment. In this work, inspired by the heterogeneous precipitation along dislocation for Mn-containing dispersoids, strain induced dislocations was introduced by prior deformation to increase the nucleation sites in the matrix. Based on the classical nucleation theory, the nucleation rate in the pre-strained specimen is improved by an order of magnitude compared with that of the as-cast specimen. Detailed electrical conductivity tests and transmission electron microscopy observations showed that prior deformation can promote the decomposition of supersaturated solid solution and successfully increase the number density of Mn-containing dispersoids, but decrease their sizes from 323 ± 83 nm to 118 ± 43 nm in long axis dimension after homogenization treatment. An improvement of 36.5 MPa in yield strength can be achieved through the enhanced dispersion strengthening mechanism. Simultaneously, the diffusion distance of Mn solute atoms dramatically increases from 0.85 μm to 27 μm due to the enhancement in diffusivity, which can be mostly attributed to the increase in diffusion paths caused by the higher density of strain-induced dislocations. Thus, the volume fraction of dispersoid free zones was decreased by 51% in the pre-strained specimen, indicating that a more uniform distribution of dispersoids in the Al matrix can be obtained by prior deformation. This work provides some insight into the enhanced dispersion strengthening effect of Mn-containing dispersoids by prior deformation, which is a promising approach to further improve mechanical properties of non-age hardenable Al alloy.

Effect of low-temperature quasihydroextrusion on the structure and physical properties of CuCrZr alloy

The work is devoted to the study of changes in the structural and physical properties of the precipitation-hardened CuCrZr alloy under the influence of low-temperature (77 K) quasihydroextrusion with various degrees of deformation at liquid nitrogen temperature with subsequent aging. Prior to quasihydroextrusion, commercial alloy samples were annealed and quenched from the premelting temperature to obtain a supersaturated solid solution of alloying elements in the copper matrix. After quasihydroextrusion, the microstructure, lattice constant, pole densities, tensile strength and yield strength, microhardness (in different cross-sections of the extrudate), and electrical conductivity of the CuCrZr alloy were studied depending on the degree of deformation by quasihydroextrusion. It is shown that the deformation degree determines the kinetics of decomposition of the supersaturated solid solution and its structure. As a result of extrusion, an anisotropic structure of the matrix and precipitates is formed, which also determines the anisotropy of material properties. Subsequent aging leads to a significant decrease in the anisotropy of properties. With an increase in the deformation degree during extrusion (before aging), a significant monotonous increase in physical and mechanical properties occurs. However, in the range of deformation degrees of 40–50%, an anomalous “jump” of all measured properties and structural parameters is observed. The study proposes a physical mechanism that explains the experimental results. The mechanism is based on the occurrence of two kinetically differently directed processes: dynamic aging and its inhibition due to an increase in the defectiveness of the material. The latter process manifests itself essentially at low temperatures. In general, low-temperature quasihydroextrusion makes it possible to obtain a complex of sufficiently high mechanical and electrical characteristics of the CuCrZr alloy at relatively low degrees of deformation for one extrusion cycle, which is facilitated by low deformation temperature.

Substitution limits and thermodynamic stability of solid solutions in HTSC based on iron and yttrium oxyarsenides

The mixing energies (interaction parameters) and the critical decomposition (stability) temperatures of Y1–xLnxFeAsO0.6 solid solutions, where Ln = La–Er, 0 < x < 1.0, were determined within the framework of the V. S. Urusov crystal-energetic approach in the approximation of regular solid solutions. Diagram of thermodynamic stability and domes of the solid solution decomposition have been plotted, which make it possible to calculate the equilibrium isomorphous substitution limits of yttrium for rare earth elements x depending on the decomposition temperature Td, or the decomposition temperature depending on the substitution limit. The results of calculation do not contradict to the experimental data found earlier in the literature for La1–xYxFeAsO0.6 and related systems La1–yYvFeAsO, La0.8Y0.2FeAsO0.7, and Y0.95La0.05FeAsO1–vH0.15. The results of this work can be useful in choosing the components’ ratio in “mixed” matrices and the dopant content in high-temperature superconductors, effective magnetic and other materials.

Decreasing the W-Cr solid solution decomposition rate: Theory, modelling and experimental verification

Tungsten-based alloys are essential materials in the nuclear fusion reactors’ development. Particularly, tungsten-chromium single solid solution is interesting for the combination of a good oxidation behaviour and lack of lower-melting-point phases. The W-Cr system has a miscibility gap though and the solid solution within the particular condition is inherently metastable/unstable and tends to decompose forming a Cr-rich phase. In this study, we have combined computer simulations and experimental work to find additional alloying elements to promote the stability of W-Cr solid solution. The results showed that alloying with Ta may result in lowering the stabilising temperature of the alloy, positively affecting the decomposition rate. Experiments performed on a W-Cr-Ta alloy showed prolonged solid solution lifetime when compared to W-Cr alloy. Formation of the third decomposed phase, enriched in Ta, was observed and changes in the chromium diffusion in the alloy were identified to be the governing factor for slowing down the decomposition.

Problems in Imaging the Decomposition of Liquid and Solid Solutions in the Ag–Cu–Ni and Ag–Cu–Pb Systems

Problems in Imaging the Decomposition of Liquid and Solid Solutions in the Ag–Cu–Ni and Ag–Cu–Pb Systems

ВЛИЯНИЕ ТЕРМИЧЕСКОЙ ОБРАБОТКИ НА СПЛАВЫ СИСТЕМЫ Al‒Mg‒SiС ИЗБЫТКОМ КРЕМНИЯ И МАЛЫМИ ЦИРКОНИЕВЫМИ ДОБАВКАМИ

The study is aimed at studying heat treatment for the formation of physical and mechanical properties in the Al-Mg-Si system with an excess of silicon and small zirconium additives. The study was carried out on the example of three alloys with different Mg/Si ratios with a zirconium content of 0.15%. The alloys were subjected to both one and two-stage heat treatment. In the course of a single-stage heat treatment, the alloys were annealed at a temperature of 375–550 °C and holding, which ranged from 10 seconds to 100 hours, followed by fixation of the microstructure in water. In addition, a multi-stage heat treatment was carried out, the annealing temperature of the first stage was varied in the range of 425–550 °C with an 8-hour exposure and subsequent fixation in water, after which the metal was subjected to a 3-hour artificial aging. After completion of the heat treatment, the microhardness and electrical conductivity were investigated. Based on the data on the change in the latter depending on the mode of heat treatment, C-curves of the decomposition of the supersaturated solid solution were constructed. For some modes of heat treatment, studies of intermetallic particles were carried out using scanning microscopy. Using scanning electron microscopy, particles were found in the alloys, similar in their chemical composition to Mg2Si, Al3(FeSi) and Zr2Si. The obtained C-curves show that the decomposition of a supersaturated solid solution begins already at a temperature of 375 °C. Using the constructed C-curves, the influence of the content of silicon, magnesium elements on the rate of decomposition of a supersaturated solid solution is shown. It has been established that the annealing temperature of 375 and 425°C adversely affects the microhardness in the alloys under consideration. After an increase in the annealing temperature to 550°C, there is practically no decrease in microhardness. The performed studies made it possible to choose the optimal mode of multi-stage heat treatment, namely heating to 550 °C for 8 hours with cooling in water, and subsequent 3-hour exposure at a temperature of 180 °C. In general, zirconium additives give an increase in microhardness by 11-25 HV compared to base alloys.