Decomposition Of Solid Solution Research Articles

Radiation tolerance of nanostructured TiAlN coatings under Ar+ ion irradiation

The radiation tolerance of TiAlN coatings under irradiation with 200 keV Ar+ ions is studied at room temperature. The ion fluence varied in the range of 1·1016–2·1017 ions/cm2. The TiAlN coatings were deposited by reactive magnetron sputtering on single crystalline silicon wafers as well as on AISI 304 stainless steel bars. Elemental composition of the coatings was investigated using Rutherford backscattering spectrometry with He+ ions of 2.53 MeV and 4.53 MeV as well as by energy-dispersive X-ray spectroscopy using 18 keV electrons. Phase composition and structure of TiAlN coatings were examined by X-ray diffraction and scanning electron microscopy. Mechanical properties of TiAlN coatings were evaluated by nanoindentation using a nanohardness tester with a Berkovich diamond tip and applying the Oliver-Pharr method. Some selective nitrogen sputtering was detected caused by the Ar+ ion irradiation. The TiAlN coatings crystallites refined under argon ion irradiation. It was found that the irradiation fluence of 2·1017 ions/cm2 is a threshold fluence, at which the solid solution decomposition starts. Ion irradiation causes mechanical properties improvement up to the fluence of 5·1016 ions/cm2. No destruction processes of the coatings such as blistering or flaking were detected for all irradiation fluences used in this study.

Formation of Finely Dispersed Structures in Alloys of Aluminum with Cobalt and Zirconium

Rapidly quenched alloys of aluminum with cobalt and zirconium are investigated using a combination of means of physicochemical analysis to study the formation of finely dispersed structures that considerably enhance the strength characteristics of materials. Rapidly quenched alloys are studied, since it is a mode of alloy treatment that allows the maximum isolation of the strengthening phase. It is found that the transfer of the single-phase structure of a supersaturated solid solution of Alsupers(Co,Zr) to Als(Co,Zr) + ZrAl3 + Co2Al9 is accompanied by an increase in hardness, due to the sequential separation of the intermetallic phases in the finely dispersed state. It is shown that the value of the dispersion hardening effect depends largely on the temperature and time parameters of the decomposition of supersaturated solid solutions.

The structure of rapidly solidified foil of the eutectic Sn – 8.8 wt. % Zn alloy

Microstructure of rapidly solidified eutectic alloy foil Sn – 8.8 wt. % Zn was studied. The alloy foil consists of solid solutions of zinc and tin. Dark equiaxed dispersed precipitates of zinc solid solution are uniformly interspersed in the matrix of tin solid solution. The parameters of the microstructure were determined. The average chord of a random secant at the sections of precipitates of a solid solution of zinc is 0.33 mm, and the specific interface surface is 0.81 mm–1. The precipitations of the tin solid solution have a microcrystalline structure. Specific surface of high angle boundaries less than 1 mm–1. The texture of the precipitates of solid solutions of tin and zinc in the foil was studied, and the pole densities of the diffraction lines of these phases are presented. The tin solid solution has the texture (100), and the zinc solid solution has the (0001) texture, which is explained by the predominant growth of grains, in which the crystalline planes of (100) tin and (0001) zinc are most closely packed and perpendicular to the heat flux. Eutectic alloy Sn – 8.8 wt. % Zn is in an unstable state. Annealing the foil causes the dissolution of small and coarsening of large particles of zinc solid solution, as well as the decomposition of a supersaturated tin solid solution. These processes cause an enlargement of the microstructure: an increase in the average particle size (dZn) of a solid solution of zinc and its volume fraction (VZn), a decrease in the specific surface (S ) of interphase boundaries.

Influence of decomposition of oversatured liquid solutions on the structure and microhardness of quickly curing alloys of the Pb–Sn system

The results of studies of the structure and microhardness of foil alloys of the lead–tin system obtained by high-speed cooling from the liquid phase are presented. The foil sample had the following dimensions: length – up to 10 cm, width – up to 1 cm, and thickness – 30–80 microns. Melt cooling rate was not less than 105 K/s. A rapidly cooled foil is chara cterized by a dispersed structure. The size of the discharge of tin and lead does not exceed 5 μm. The specific surface of the interfacial boundaries achieve 1.7 μm–1. Due to supercooling, a microcrystalline structure forms in the foil. The average lengths of chords of random secants on lead and tin grain sections in the Pb–73 at.% Sn alloy foil are 0.8 and 1.8 μm respectively. The texture of (111) lead and (100) tin is formed in the foil of alloys of the lead – tin system under certain conditions. The formation of the structure of lead alloys containing from 20 to 95 at.% tin is due to the occurrence of spinodal decomposition of a supersaturated liquid solution, and, in other alloys, due to decay by the mechanism of formation and growth of nuclei of crystalline phases. The stratification of the liquid solution leads to the formation of areas enriched in lead and tin, which contribute to the formation of crystallization centers that are equally distributed in the volume of the foil. The microhardness of the foil alloys, whose compositions are close to eutectic, is less than the microhardness of massive alloys of the same composition, which is associated with the softening effect of grain boundaries and interphase boundaries. Exposure of these alloys at room temperature causes an increase in microhardness due to a decrease in slippage at the boundaries. The decomposition of supersaturated solid solutions of Pb–5 at.% Sn and Sn–1 at.% Pb alloys leads to a decrease in microhardness due to the weakening of the effect of the solid solution hardening mechanism. The results of the study can be used to create fusible solders, bearing alloys, alloys for cable sheaths with improved physicochemical properties.

Quantitative Phase Analysis by X-ray Diffraction—Doping Methods and Applications

X-ray powder diffraction is an ideal technique for the quantitative analysis of a multiphase sample. The intensities of diffraction lines of a phase in a multiphase sample are proportional to the phase fraction and the quantitative analysis can be obtained if the correction for the absorption of X-rays in the sample is performed. Simple procedures of quantitative X-ray diffraction phase analysis of a multiphase sample are presented. The matrix-flushing method, with the application of reference intensities, yields the relationship between the intensity and phase fraction free from the absorption effect, thus, shunting calibration curves or internal standard procedures. Special attention is paid to the doping methods: (i) simultaneous determination of the fractions of several phases using a single doping and (ii) determination of the fraction of the dominant phase. The conditions to minimize systematic errors are discussed. The problem of overlapping of diffraction lines can be overcome by combining the doping method (i) and the individual profile fitting method, thus performing the quantitative phase analysis without the reference to structural models of particular phases. Recent suggestions in quantitative phase analysis are quoted, e.g., in study of the decomposition of supersaturated solid solutions—intermetallic alloys. Round Robin on Quantitative Phase Analysis, organized by the IUCr Commission on Powder Diffraction, is discussed shortly. The doping methods have been applied in various studies, e.g., phase transitions in titanium dioxide, biomineralization processes, and phases in intermetallic oxide systems and intermetallic alloys.

Твердые растворы AlGaInSbAs, выращенные на подложках InAs методом зонной перекристаллизации градиентом температуры

Growth of AlGaInSbAs solid solutions on InAs substrates from liquid phase in a temperature gradient field is discussed. There are calculated parameters and studied luminescent properties and spectral characteristics of AlGaInSbAs solid solutions isoperiodic to InAs substrates. Within the model of regular solutions, an analysis of heterophased neutrality in Al–Ga–In–Sb–As system is carried out. Regions of hermodynamic stability to spinodal decomposition of AlGaInSbAs solid solutions and isoperiodicity intervals to InAs substrate are revealed.

The effect of transition metals on the structure and hardening of Al-Mg-Si alloys after cold plastic deformation

The effects of equal-channel angular pressing (ECAP) and rotary swaging (RS) on the change in strength properties during aging at 170 ° C of Al-Mg-Si alloys doped with Sc, Zr and Hf additions was studied. The methods of measuring hardness, electrical resistivity, testing mechanical properties, light and transmission electron microscopy were used. The higher hardening effect compared to the initial state was found in the alloys after ECAP than after RS, whereas the strength properties (tensile strength and yield strength) were higher for alloys subjected to RS than ECAP. Al-Mg-Si alloys with the combined additives of scandium with zirconium and scandium with hafnium showed practically the same values of hardness and strength properties at tensile testing during aging. The reason is in the identical nature of the decomposition of the supersaturated solid solution. It is determined by the sequence of precipitation of the strengthening phase Mg2Si and (Sc1-x, Zrx) Al3 and (Sc1-x, Hfx) Al3 dispersoids which impede the movement of dislocations both in alloys after deformation and after aging.

Особенности фазовых переходов в висмутсодержащих упругонапряженных гетеросистемах AlGaInSbBi-InSb

In this paper the features of phase transformations in elastically stressed Al–Ga–In–Sb–Bi heterosystems and its subsystems In–Sb–Bi and Al–In–Bi are discussed. Isotherms for the aforesaid heterosystems and its subsystems are researched at temperatures from 653 to 923 K. The critical temperatures and critical point coordinates of spinodal decomposition of AlGaInSbBi solid solution are determined with regard to the coherent deformation energy. The elastic stresses effect on the thermodynamic behavior of the AlGaInSbBi–InSb heterosystem is investigated.

Влияние механизма дисперсионного твердения на закономерности пластической деформации и разрушения ванадийсодержащей высокоазотистой аустенитной стали

Nitrogen alloying of austenitic steels increases their corrosion resistance and improves mechanical properties. During heat treatment, high-nitrogen austenitic steels tend to the precipitation hardening and the increase of strength characteristics. In the current paper, the authors studied the effect of the duration of age-hardening at the temperatures of 700 °С and 800 °С on the structure, phase composition, plastic flow behavior, and fracture mechanisms of V-alloyed high nitrogen chrome-manganese austenitic Fe-19Cr-22Mn-1.5V-0.3C-0.86N (mass %) steel. The study revealed that after water-quenching at 1200 °С, the specimens possess the high strength properties, ductility and contain large (300-500 nm) (V,Cr)(N,C) particles. Aging at temperatures of 700 °С and 800 °С facilitates complex reactions of austenite discontinuous decomposition with the Cr 2 N-plate formation in grains and continuous decomposition with the formation of vanadium nitride-based particles in austenite. During the long-term aging (50 h at 700 °C and 10 h at 800 °C), the intermetallic σ-phase appears in specimens. At age-hardening, the observed phase transformations cause the changes in macro- and micro-mechanism of fracture in the specimens of steel under the study. In the initial state, the specimens show mainly the ductile transgranular fracture. After age-hardening, the fracture mechanism changes into the mixed mechanism with the elements of brittle intergranular and ductile transgranular fractures. When increasing the duration of aging and implementation of complex reactions of decomposition of solid solution, the specimens are fractured by the quasi-cleavage mechanism. The specimens aged at temperatures of 700 °С and 800 °С have quite similar precipitation hardening mechanisms, though the increase in aging temperature leads to the rising of the decomposition rate of solid solution. The sequence of transformations described above and the corresponding sequence of changes in the mechanisms of steel fracture are implemented faster when increasing the aging temperature.

Effect of annealing environment on the microstructure and mechanical property of CrWN glass molding coating

The CrWN glass molding coating was synthesized by plasma enhanced magnetron sputtering (PEMS). The effect of annealing environment (e.g., vacuum, N2 and Air) on the microstructure and mechanical property of as-deposited coating was investigated by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM) and nanoindentation tests. Results showed that the as-deposited coating exhibited dense columnar structure consisting of multilayer CrN and W2N phases. The vacuum annealed coating showed similar thickness to that of as-deposited coating, but underwent visible surface coarsening because of slight oxygen erosion. The N2 and air annealed coatings suffered from varying degree of oxidation damage accompanied by the formation of mixed WO3-CrWO4 phases, which consequently resulted in severe thickness expansion and surface coarsening. The vacuum annealing induced a spinodal decomposition of supersaturated solid solution to form nm-sized CrN and W2N domains. Strain fields originating from the lattice mismatch eventually caused a pronounced age-hardening in the vacuum annealed coating. Whereas the N2 and air annealed coatings showed significant mechanical degradation because these loose WO3-CrWO4 oxides degraded the stable matrix structure. Our results clearly demonstrated that vacuum environment effectively suppressed the oxidation damage and mechanical degradation of glass molding coating.

Decomposition of Supersaturated Solid Solution during Non-isothermal Aging and Its Effect on the Physical Properties and Microstructure of the Ag-Cu7.5 Alloy

The aim of the study was to examine the effect of supersaturated solid solution decomposition during non-isothermal aging on the microstructure and selected physical and mechanical properties of the Ag-7.5 wt.% Cu alloy. The decomposition mechanism was determined by complex research methods, i.e., physical properties testing, microstructure examinations, as well as hardness measurement. Decomposition of Ag-Cu7.5 supersaturated solid solution during heating has two stages. The first stage involves a significant increase in hardness and has no effect on electrical conductivity. During the second stage, growth of discontinuous precipitates and an increase in hardness and electrical conductivity are observed. Discontinuous precipitation cells consist of βCu rods and plates surrounded by αAg phase. Obtained activation energy of this microstructural evolution is lower than its values presented in the literature.

Effects of hot forming cold die quenching and inter-pass solution treatment on the evolution of microstructure and mechanical properties of AA2024 aluminum alloy after equal channel angular pressing

The aim of this research is to investigate the effect of hot forming cold die quenching (HFQ) equal channel angular pressing (ECAP) on the microstructural evolution and mechanical properties of AA2024 aluminum alloy. For this purpose, solution treated AA2024 aluminum alloy was initially ECAPed in HFQ and water quenched (WQ). Microstructural evolutions, dislocation density, and mechanical properties were investigated after up to 3 (WQ-ECAP) and 5 (HFQ-ECAP) passes of deformation. Intermediate solution treatment was conducted after each ECAP pass. The samples underwent aging treatment after deformation. Large amount of shear banding was observed in samples after the first ECAP pass which was reduced in the successive passes of ECAP through intermediate solution treatment. Tensile properties and microhardness enhanced by increasing number of ECAP passes. However; after the fifth pass of HFQ-ECAP, sudden decrease in mechanical properties was observed. Partial decomposition of supersaturated solid solution was found to occur at higher strains. Mechanical properties and deformability were improved in the HFQ-ECAP samples with respect to WQ-ECAP.

Structural and Phase Transformations in Al–Li–Cu–Mg–Zr–Sc–Zn Alloy upon Storage after Megaplastic Deformation

Structural and phase transformations in a commercial multicomponent aluminum–lithium alloy have been studied electron-microscopically upon storage after mega-plastic deformation by high-pressure torsion. It has been shown that the arising deformation structure of the alloy is unstable, and upon subsequent storage at room temperature it is transformed via a complex reaction of in situ recrystallization and decomposition of the supersaturated solid solution. The character of the transformation is determined by the regime of the previous mega-plastic deformation and by the duration of the storage.

Strength properties and structure of CuCrZr alloy subjected to low-temperature KOBO extrusion and heat treatment

KOBO extrusion of metals and alloys strongly activates the point defect generation processes, as a result of which they reach a concentration exceeding the equilibrium level by many orders of magnitude. This leads to significant acceleration of diffusion phenomena which in heat-treatable alloys may cause disturbance of the thermodynamic equilibrium between the solid solution decomposition and dissolution of precipitates. In this work, measurements of mechanical and electrical properties and structural observations Cu1Cr0.1Zr alloy subjected to low-temperature KOBO extrusion at different stages of multi-variant heat treatment were conducted. In addition, the geometry of the extruded alloy’s flow zone was analyzed and the obtained results made it possible to assess the effectiveness of experimental procedures, including product formation with high extrusion ratio λ, aimed at achieving of high and thermally stable functional properties of the material.

Effect of Holmium and Ytterbium on Age Hardening of High-Strength Magnesium Alloy IMV7-1 of the Mg – Y – Gd – Zr System

The kinetics of decomposition of supersaturated magnesium solid solution and of the accompanying hardening of the latter at 200°C in cast alloy IMV7-1 of the Mg – Y – Gd – Zr system alloyed with two rare-earth metals, i.e., holmium and ytterbium, is studied. Holmium and ytterbium are introduced into IMV7-1 by substituting two other rare-earth metals, i.e., yttrium and gadolinium. It is shown that the presence of holmium and ytterbium instead of yttrium and gadolinium does not change the decomposition behavior of the supersaturated solid solution but decelerates this process and lowers the effect of age hardening.

Spinodal decomposition with formation of composition oscillations at low temperature GaInP - GaAs synthesis

The Cahn-Hillard equation is adapted to consider the spinodal decomposition process of semiconductor solid solutions. The obtained differential equation for the decomposition of a material is used to describe the composition modulation effect observed during the synthesis of GaxIn1-xP-GaAs heterostructures. The numerical simulation of the process of spinodal decomposition of the GaxIn1-xP solid solution is performed. The intervals of the thermodynamic parameters for the technological process of the structures synthesis, in which the composition modulation effect should appear, are found.

Structure and hydrogen permeability of V–15Ni alloy

The structure of the V–15Ni at.% alloy before and after hydrogen permeability tests was investigated by means of XRD and SEM with EDS analysis. We have found that decomposition of supersaturated V-based solid solution with variable Ni content occurred during testing. The volume fraction of the solid solution decreased and the fraction of V3Ni phase increased during permeability testing, thus bringing the alloy to nearly equilibrium. The membrane without Pd coating showed satisfactory hydrogen fluxes with a significant impact of the surface dissociation rate of hydrogen. The shape of hydrogen permeation curves at the downstream side of the membrane at various temperatures was unusual. We attribute it to the high concentration of dissolved hydrogen in the metal lattice and its effect on the hydrogen diffusivity and solubility. In addition, the multiphase structure with non-uniform distribution of nickel both between the phases and within the BCC solid solution (and, consequently, different hydrogen concentrations) may cause dilatation or compressing effect on neighbouring micro-volumes of the alloy.

Regularities of microdefect formation in silicon during heat treatment for internal getter synthesis

Gettering is defined as a process by which metal impurities in the device region are reduced by localizing them in predetermined, passive regions of the silicon wafer. Internal or intrinsic gettering is an effective way to reduce the contamination in active regions. The generation of internal getters is based on the decomposition of the supersaturated oxygen solid solution in silicon, which favours the formation of a complex defect system in silicon that consists of various precipitate/dislocation agglomerates. Regularities of microdefect formation during oxygen solid solution decomposition in silicon have been studied. We show that actual solid solution supersaturation, temperature and heat treatment duration determine the structure of the solid solution. Combining these factors, including heat treatment parameters, one can control solid solution decomposition rate and SiOx precipitate sizes and quantity. The methods of X-ray diffuse scattering and transmission electron microscopy have shown high efficiency for studying the effect of heat treatment in crystals. For annealing at 450 °C, solid solution decomposition occurs at high supersaturation degrees, and concentration inhomogeneity regions may form at an early decomposition stage over the actual annealing time (up to 40 h). With an increase in the temperature of subsequent annealing to 650 °C, local regions with above-average oxygen supersaturation degrees increase the efficiency of oxygen solid solution decomposition. Further, an increase in annealing temperature to T > 1000 °С results in a more intense generation of the largest precipitates at the expense of the smaller ones. Once the precipitate sizes become sufficiently large, the elastic stresses start to relax, leading to partial incoherence and the generation of dislocations around the particles. This type of defect structure seems to be the most efficient getter.

Effect of Severe Plastic Deformation on the Structure and Properties of the Aluminum Alloy System Al-Cu-Mg

The structure and properties of discs from cast coarse-grained D16 alloy have been investigated with the help of optical metallography and transmission electron microscopy, after the traditional heat treatment (HT) modes or subjected to high pressure torsion (HPT) under pressure in 6 GPa at room temperature. Standard HT modes included: Т4 (hardening 495°С + natural aging at room temperature for 5 days) and Т6 (hardening 495°С + artificial aging at 185°С for 10 hours). It is shown that after HT of alloy D16 according to modes T6 and Т4, the sizes of the structural elements, compared with the original, decreased by about 4,8 times and the microhardness increased by 1,6 times. It is shown that after one or ten rotates of HPT in D16 alloy the sizes of structural elements, in comparison with initial, decreased by 393 and 899 times, and microhardness increased by 2,4 and 2,9 times, respectively. Detection of hardening hard, brittle and high-alloy copper γ2- phases (Cu9Al4) indicates the passage in the HPT process of the decomposition of a supersaturated solid solution (dynamic aging) in the planes of a local shift.

Aluminum-Matrix Natural Composite Material Based on the Al–Ca–Ni–La–Fe System

The primary crystallization concentration region of the aluminum solid solution (Al) is refined using computational analysis in the Thermo-Calc program, including the construction of liquidus surfaces and polythermal sections of the Al–Ca–Ni–La–Fe system, as well as experimental microstructural analysis using scanning electron microscopy. This region can be considered promising for the formation of new aluminum-matrix natural eutectic-type composite materials containing above 20 vol % of intermetallic particles in the structure. The investigation into the microstructure of a promising composition with the formula, wt %, Al–4Ca–2Ni–1La–0.6Fe revealed that it contains up to 23 vol % of Al4Ca and Al9FeNi intermetallic phases of a eutectic nature according to the calculation. Separate crystals of these phases in the eutectic composition have submicron sizes, notably, a length of 250–400 nm and a thickness of 100–200 nm. It is also established that no formation of the Al4La intermetallic phase predicted by the thermodynamic calculation is observed, while lanthanum itself is completely dissolved in the Al4Ca calcium-containing phase. An analysis of the microstructure and hardness during stepped annealing has shown that codoping of the Al–4Ca–2Ni–1La–0.6Fe alloy by zirconium and scandium (0.2% Zr and 0.1% Sc) leads to precipitation hardening due to the decomposition of the (Al) solid solution and further formation of coherent nanoparticles of the L12 phase—Al3(Zr, Sc) up to 20 nm in size. The results of studying the mechanical properties under uniaxial tension testing of cylindrical castings of the Al–4Ca–2Ni–1La–0.6Fe–0.2Zr–0.1Sc alloy show a relatively high level of strength characteristics (σв of 265 MPa and σ0.2 of 177 MPa) with the conservation of the elongation acceptable for the composite material (~2%). Thus, it is shown based on these results that the Al–Ca–Ni–La–Fe system is promising for the fabrication of new aluminum-matrix natural composite materials.