Formation Of Supersaturated Solid Solution Research Articles

Thermodynamic modelling application for prediction of diffusion formation of supersaturation solution

Abstract In this paper the effect of diffusion formation of supersaturated solid solution in the Al–Ge system is discussed. It was shown that at relatively low temperatures of diffusion annealing, Ge concentration in Al-based solid solution became higher than the solubility limit at given temperatures. The maximal concentration of Ge was determined by extrapolation of the diffusion profile on the Ge/Al interface. Analysis of diffusivity of Al in Ge allowed to suggest that slow diffusion in Ge restricts the formation of Ge-based solid solution. Qualitative approach confirmed this suggestion.

Metastable aluminum boride: density functional theory study of prerequisites of formation

AbstractAluminum borides have significant practical interest as energetic additives to fuels, explosives and propellants due to their favorable thermodynamic and kinetic characteristics. Density functional theory calculations with periodic boundary conditions have been performed to evaluate the enthalpy of formation of two aluminum borides: the well‐known aluminum diboride AlB2 and the metastable Al1.28B phase, which precedes the formation of AlB2 during heat treatment of mechanically activated composite aluminum‐boron powders, as well as aluminum ion‐implanted with boron. The calculated formation enthalpy of AlB2 is −3.6 kcal/mol, which agrees well with estimates from literature. The enthalpy of formation of Al1.28B, calculated for the first time, is 4.8 ± 0.4 kcal/mol. To understand the prerequisites for the formation of Al1.28B observed in experiments, the enthalpy of formation of supersaturated solid solutions of B in Al has been evaluated. The reasons for the preferential formation of the metastable Al1.28B phase over the thermodynamically stable AlB2 phase are discussed.

Microstructure Formation and Mechanical Properties of Metastable Titanium-Based Gradient Coating Fabricated via Intense Pulse Ion Beam Melt Mixing.

The unique flash heating characteristics of intense pulsed ion beams (IPIB) offer potential advantages to fabricate high-performance coatings with non-equilibrium structures. In this study, titanium-chromium (Ti-Cr) alloy coatings are prepared through magnetron sputtering and successive IPIB irradiation, and the feasibility of IPIB melt mixing (IPIBMM) for a film-substrate system is verified via finite elements analysis. The experimental results reveal that the melting depth is 1.15 μm under IPIB irradiation, which is in close agreement with the calculation value (1.18 μm). The film and substrate form a Ti-Cr alloy coating by IPIBMM. The coating has a continuous gradient composition distribution, metallurgically bonding on the Ti substrate via IPIBMM. Increasing the IPIB pulse number leads to more complete element mixing and the elimination of surface cracks and craters. Additionally, the IPIB irradiation induces the formation of supersaturated solid solutions, lattice transition, and preferred orientation change, contributing to an increase in hardness and a decrease in elastic modulus with continuous irradiation. Notably, the coating treated with 20 pulses demonstrates a remarkable hardness (4.8 GPa), more than twice that of pure Ti, and a lower elastic modulus (100.3 GPa), 20% less than that of pure Ti. The analysis of the load-displacement curves and H-E ratios indicates that the Ti-Cr alloy coated samples exhibit better plasticity and wear resistance compared to pure Ti. Specifically, the coating formed after 20 pulses exhibits exceptional wear resistance, as demonstrated by its H3/E2 value being 14 times higher than that of pure Ti. This development provides an efficient and eco-friendly method for designing robust-adhesion coatings with specific structures, which can be extended to various bi- or multi-element material systems.

Structure formation and peculiarities of crystallisation of lead-free tin – zinc alloys obtained by rapid solidification

The results of the study of the microstructure of lead-free alloys of the tin – zinc system obtained by rapid solidification at a cooling rate of at least 105 K/s are presented. In tin and zinc alloys with concentrations of 1.2–2.0 wt. % Zn and 1.5 wt. % Sn, respectively, during rapidly cooling of the melt, the alloying element is captured. The formed solid solutions are supersaturated and at room temperature disintegrate according to the mechanism of formation and growth of nuclei of a new phase. The average size of zinc and tin precipitates after holding the foil for two days does not exceed 0.5 μm. Melts of compositions Sn – 4.4–15.0 wt. % Zn after rapidly cooling are supercooled and supersaturated by two components and experience spinodal decomposition (stratification) followed by the formation of supersaturated solid solutions based on tin and zinc, which disintegrate at room temperature. The average size of zinc precipitates in non-equilibrium eutectic does not exceed 2 μm. In rapid solidificated foils of alloys containing 50–80 wt. % Zn, a two-phase structure is formed from solid solutions based on tin and zinc. The average size of tin precipitates does not exceed 1 μm. As the crystallisation front moves away from the contact surface of the foil with the surface of the mold, the tin particles become larger and the specific surface of the interphase boundary decreases.

A Critical Review on Al-Co Alloys: Fabrication Routes, Microstructural Evolution and Properties

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading to a variety of different microstructural features. The effect of the fabrication method on the microstructure is crucial, affecting the morphology and volume of the precipitates, the formation of supersaturated solid solutions and the development of amorphous phases. In addition, the alloy composition has an effect on the type and volume fraction of intermetallic phases formed. As a result, alloy properties are largely affected by the microstructural outcomes. This review focuses on highlighting the effect of the fabrication techniques and composition on the microstructure and properties of Al-Co alloys. Another goal is to highlight areas in the field that are not well understood. The advantages and limitations of this less common category of Al alloys are being discussed with the scope of future prospects and potential applications.

Effect of V content on corrosion behavior of high-energy ball milled AA5083

AA5083 alloys with V additions were produced in the powder form by high-energy ball milling and consolidation by spark plasma sintering and cold compaction. X-ray diffraction and energy dispersive X-ray spectroscopy analysis indicated the formation of supersaturated solid solution and grain refinement below 100 nm. Corrosion behavior was investigated using electrochemical impedance spectroscopy, cyclic potentiodynamic polarization, and immersion corrosion tests followed by surface analysis. The composition of the passive film was obtained via X-ray photoelectron spectroscopy. The corrosion resistance of the AA5083 was significantly improved due to the addition of V and high-energy ball milling.

Films of immiscible systems obtained by three-electrode ion-plasma sputtering

The data on the ion-plasma sputtering of composite targets of the systems (Fe, Co, Ni) – (Ag, Bi) whose components do not mix in the liquid state is presented. The lattice parameters and sizes of crystals of metastable phases were determined. The films deposited show the formation of supersaturated solid solutions ore nanocrystalline and amorphous phase. The decomposition of metastable phase is accompanied by precipitation of equilibrium solid solutions based on incoming elements ore an intermediate phase. We studied the thermal stability of metastable states in (Fe, Co, Ni) – (Ag, Bi) films, the electrical and hysteresis magnetic characteristics of as-deposited and heat-treated films and established the optimum film compositions with precise values of temperature coefficient of resistivity (∼ 10−5 K−1) and high coercive force (H c ∼ 150 kA/m). Such films can be promising for use as thin-film precision resistors and magnetic information carriers with an increased recording density.

Effect of the Mechanical Alloying and Spark Plasma Sintering on Microstructure, Phase Composition and Chemical Elements Distribution of Nb-Si Based Composite

Synthesis of the Nb-Si in-situ composite was attempted by mechanical alloying of element powders in vario-planetary ball mill. The particles size distribution was measured by laser diffraction, microstructures were examined with scanning electronic microscope, and the phase constituent were analyzed by X-ray diffraction. The amorphization of the Si during mechanical alloying, large amount of deformation of Nb crystal structure, and after all – the formation of supersaturated solid solution of Nb was observed. To stabilize microstructure and phase composition, a spark plasma sintering was attempted. After SPS microstructure consist of three main phases – Nbss, Nb5Si3 and Nb3Si.

Microstructure of Rapidly Solidified Alloys of the Sn–Zn–Bi–In System

The results of a study of the phase composition and microstructure of foils of Sn–8.0 Zn–3.0 Bi–X In (X = 1.5, 2.5, 4.5, 9.0) (wt %) alloys formed by rapidly quenching from the melt at a cooling rate of up to 5 × 105 K/s have been presented. The dependence of the phase composition of the rapidly quenched foils on the concentration of In has been determined. It has been shown that, in rapidly quenched foils, crystallization occurs with the formation of supersaturated solid solutions based on β-Sn and γ phase (Sn4In). The mechanisms and rates of decomposition of the supersaturated solid solutions at room temperature have been established. The specific features of the formation of the microstructure of the foils have been discussed. The grain structure has been studied by the electron back-scatter diffraction (EBSD) method; the formation of an elongated shape of grains and the high specific surface area of small-angle boundaries has been explained.

Electrocrystallization and Properties of Supersaturated Solid Solutions of Copper

The role of the alloying element in the formation of the structure and properties of electrolytic copper alloys has been determined. The X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) have shown that electrochemical alloying of copper with low-melting metals leads to the formation of supersaturated solid solutions (SSS) on the cathode, crushing of the crystal structure, smoothing of the surface relief, hardening of the deposits obtained, increasing their solderability and corrosive resistance to acidic media.

Fabrication of Al-Zn solid solution via friction stir processing

The present study demonstrates that friction stir processing (FSP) can be used as a mechanical alloying tool to process solid solution. Zn was incorporated in commercially pure aluminium by multi-pass FSP leading to its dissolution and formation of supersaturated solid solution which was confirmed by X-ray diffraction and scanning electron microscopy. The hardness across the stir zone matched with the distribution of Zn and was significantly improved compared to the base metal. The supersaturated solid solution that formed in the first pass, partially decomposed during the second pass, leading to the formation of fine Al-Zn precipitates. Thermal stability of the microstructure against abnormal grain growth was also improved after the second pass due to the pinning effect of the grain boundary precipitates. FSP also caused grain refinement of the alloy yielding fine equiaxed grains in the range of 4–6μm with a high fraction (>67%) of high angle grain boundaries. Such microstructure is conducive for isotropic properties and the fact that the microstructure is stable against thermal cycles make the process suitable for selective alloying for location specific property enhancement.

Sliding wear induced subsurface microstructural evolution in nanocrystalline Nb-Ag binary alloys and its impact on tribological performance

Powders of Nb and Ag were first subjected to mechanical alloying to force the formation of supersaturated solid solutions and then compacted to near full density using spark plasma sintering. During the sintering process, Ag precipitated out from the Nb matrix along the Nb grain boundaries, with the size of the precipitates depending on the nominal chemical composition. Pin-on-disk wear tests show that the nanostructured Nb-Ag alloys show good wear resistance. A wear factor of 10−5mm3/(N·m) was observed upon sliding against stainless steel 440C. Ag concentration has a significant effect on the wear rate and wear modes of Nb-Ag alloys. For higher Ag concentration with larger initial Ag precipitate size and lower hardness, severe plastic deformation (SPD) during wear induced the spontaneous formation of alternating Nb and Ag nanolayers. These nanolayered structures remain stable up to the sliding surface, leading to a reduction in the wear rate. In contrast, for lower Ag concentration with smaller Ag precipitate size and higher hardness, SPD can dissolve the Ag precipitates and force the formation of supersaturated solid solutions with equiaxed nanograins below the sliding surface. This results in an increase in the wear rate.

Enhanced mechanical properties of an Al-Mg-Si alloy by repetitive continuous extrusion forming process and subsequent aging treatment

The microstructure and mechanical properties of a continuous casting and rolling Al-Mg-Si alloy subjected to repetitive continuous extrusion forming process (R-Conform process) and subsequent artificial aging treatment are investigated in this work. The results show that R-Conform process can effectively improve both tensile strength and ductility of the Al-Mg-Si alloy, in which tensile strength and ductility are simultaneously improved with increasing Conform passes. The enhanced mechanical properties are associated with the progressively formation of supersaturated solid solution and refined and homogenous distributed substructures with high dislocation densities during R-Conform process. For the post-R-Conform artificial aged Al-Mg-Si alloy at 175°C for 8h, fine and homogeneous β'' precipitation strengthening phases are formed due to the great driving force of dynamic strain redissolution (DSR) during R-Conform process. Thus, compared to the aged continuous casting and rolling Al-Mg-Si alloy, an increase of ~18.9% in tensile strength and ~23.9% in ductility are obtained after seven R-Conform passes and followed by aged at 175°C for 8h.

Structural features of Ni-Cr-Si-B materials obtained by different technologies

This study considers the structural features of Ni-Cr-Si-B (Ni - base; 15.1 % Cr; 2 % Si; 2 % B; 0.4 % C) materials obtained by different methods. The self-fluxing coatings were deposited by plasma spraying on the tubes from low carbon steel. Bulk cylinder specimens of 20 mm diameter and 15 mm height were obtained by spark plasma sintering (SPS). The structure and phase composition of these materials were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The major phases of coatings and sintered materials are γ-Ni, Ni3B, CrB and Cr7C3. We demonstrate that the particle unmelted in the process of plasma spraying or SPS consist of γ-Ni-NEB eutectic and also CrB and Cr7C3 inclusions. The prolonged exposure of powder to high temperatures as well as slow cooling rates by SPS provide for the growth of the structural components as compared to those of plasma coatings materials. High cooling rates at the plasma spraying by melted particles contribute to the formation of supersaturated solid solution of Cr, Si and Fe in γ-Ni. The structure of the melted particles in sintering material has gradient composition: the core constituted of Ni grains of 10 μm with γ-Ni-Ni3B eutectic on the edges. The results of the experiment demonstrate that the sintering material has a smaller microhardness in comparison with plasma coatings (650 and 850 MPa, respectively), but at the same time the material has higher density (porosity less than 1 %) than plasma coatings (porosity about 2.. .3 %).

Mechanical Properties and Fracture Behavior of Cu-Co-Be Alloy after Plastic Deformation and Heat Treatment

Mechanical properties and fracture behavior of Cu-0. 84Co-0. 23Be alloy after plastic deformation and heat treatment were comparatively investigated. Severe plastic deformation by hot extrusion and cold drawing was adopted to induce large plastic strain of Cu-0. 84Co-0. 23Be alloy. The tensile strength and elongation are up to 476. 6 MPa and 18%, respectively. The fractured surface consists of deep dimples and micro-voids. Due to the formation of supersaturated solid solution on the Cu matrix by solution treatment at 950 °C for 1 h, the tensile strength decreased to 271. 9 MPa, while the elongation increased to 42%. The fracture morphology is parabolic dimple. Furthermore, the tensile strength increased significantly to 580. 2 MPa after aging at 480 °C for 4 h. During the aging process, a large number of precipitates formed and distributed on the Cu matrix. The fracture feature of aged specimens with low elongation (4. 6%) exhibits an obvious brittle intergranular fracture. It is confirmed that the mechanical properties and fracture behavior are dominated by the microstructure characteristics of Cu-0. 84Co-0. 23Be alloy after plastic deformation and heat treatment. In addition, the fracture behavior at 450 °C of aged Cu-0. 84Co-0. 23Be alloy was also studied. The tensile strength and elongation are 383. 6 MPa and 11.2%, respectively. The fractured morphologies are mainly candy-shaped with partial parabolic dimples and equiaxed dimples. The fracture mode is multi-mixed mechanism that brittle intergranular fracture plays a dominant role and ductile fracture is secondary.

Separation in liquid and the formation of supersaturated solid solutions in Fe–Cu alloys upon rapid laser melting

The structure of compacted specimens produced using the rapid laser melting of ultradispersed Fe–50 wt % Cu powders has been studied. The original powder was produced via the mechanical milling of iron and copper powders in a planetary-type ball mill. It has been found that the structure of the compacted specimens produced using rapid laser melting exhibits signs of the initial stages of separation in supercooled liquid. It has been shown using X-ray diffraction analysis as well as scanning and transmission electron microscopy that the final structure contains a supersaturated (Fe; Cu) solid solution formed from the high-speed movement of the solidification front and the nonequilibrium capture of copper by the moving front.

Synthesis of stable and metastable phases in the Ni[sbnd]Si system by mechanical alloying

Mechanical alloying (MA) of NiSi elemental powder blends was undertaken to synthesize the NiSi and NiSi2 compounds having a very narrow homogeneity range, a difficult situation to achieve by conventional melting and solidification methods. Elemental powder blends corresponding to Ni75at.% Si and Ni80at.% Si compositions, were subjected to MA in a high-energy SPEX shaker mill to study phase evolution as a function of milling time. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques were used to characterize the phases present in the as-milled powders. It was noted that a supersaturated solid solution had formed in the early stages of milling containing up to 18.2at.% Si and 20.5at.% Si in the Ni75at.% Si and Ni80at.% Si blends, respectively. After 2h of milling, the equilibrium intermetallic NiSi phase started to form, and its amount increased with increasing milling time. On continued milling for about 4h, the NiSi phase that had formed earlier and the remaining free Si powder reacted to form the equilibrium intermetallic NiSi2 phase. Although, under equilibrium conditions, a mixture of both NiSi2 and Si phases is expected to be present in both the Ni75at.% Si and Ni80at.% Si compositions investigated, only the NiSi2 phase was present in both the powder blends after 15h of milling. This constitution in the milled powder has been associated with a partial loss of Si content during milling of the powder blends, confirmed by EDS analyses. Reasons for the observed formation of supersaturated solid solutions and the increased homogeneity range for the NiSi2 intermetallic have been explained.

The Role of Grain Boundaries and other Defects on Phase Transformations Induced by Severe Plastic Deformation

During the past two decades, processing of ultrafine grained materials using severe plastic deformation techniques has attracted great interest in the scientific community. Although the up-scaling of processes and the lack of ductility of ultrafine grained alloys are still some important challenges, these techniques look promising because they produce bulk materials free of porosities. More recently, some strategies to combine precipitation hardening and ultrafine grained structures have been proposed. It has also been shown that nanoscaled composite materials could be successfully processed. This experimental work rose however some very fundamental scientific questions about the influence of severe plastic deformation on the precipitation mechanisms or on the formation of supersaturated solid solution through mechanical mixing. The driving force and the thermodynamics of these phase transformations are of course affected by the high amount of energy stored in severely deformed alloys, especially as interfacial energy. But grain boundaries, with the help of dislocations and point defects, also play an important role in the kinetics. In this paper, it is proposed to shortly review these phenomena and the underlying mechanisms with a special emphasis on the contribution of grain boundaries.

Nanostructure and mechanical behavior of metastable Cu–Cr thin films grown by molecular beam epitaxy

Metastable binary Cu–Cr alloys with nominal film thicknesses of 300nm and chemical compositions in the range of 4–93at.% Cr were synthesized via co-evaporation using molecular beam epitaxy. All films were grown onto Si(100) substrates at deposition rates of ∼0.05nms−1. The film microstructures were studied by using transmission electron microscopy and X-ray diffraction. The mechanical properties were investigated by the nanoindentation technique. Depending on the chemical composition, three types of thin film microstructures are observed, which all exhibit tensile residual stresses. For a Cr concentration of 4at.% a single-phase face-centered cubic (fcc) film was formed, whereas single-phase body-centered cubic (bcc) films were observed for Cr concentrations ⩾33at.%. In the case of a Cu85Cr15 film, a two-phase fcc and bcc structure is formed. An increase of the atomic fraction of Cr induces a significant refinement of grain sizes, from ∼100nm for a Cu96Cr4 alloy to ∼30nm in the case of a Cu20Cr80 alloy. Consequently, the hardness of the alloy films increased from 5.5 to 11.8GPa. In addition, the formation of supersaturated solid solutions of Cr in single-phase fcc Cu films and Cu in single-phase bcc films was observed. Predictions of existing models of solid solution and grain boundary strengthening were evaluated and correlated with the mechanical properties of the films with respect to film compositions and grain sizes.

Mixing Enthalpies of Melts and Thermodynamic Assessment of the Cu–Fe–Cr System

The mixing enthalpies of ternary liquid alloys in the Cu–Fe–Co system have been studied by calorimetric method at 1873 K and x Cr = 0–0.45. The phase transformations in the Cu–Fe–Cr system have been examined using methods of physicochemical analysis. The thermodynamic assessment of the ternary system has been carried out in the framework of the CALPHAD method. The set of self-consistent parameters for thermodynamic models of the phases has been obtained taking into account experimental data of the present work and information on phase transformations. The isothermal and vertical sections of the phase diagram, liquidus and solidus surfaces, as well as metastable miscibility gaps of supercooled liquid alloys have been calculated. The degrees of supercooling for metastable liquid phase immiscibility have been assessed. The composition ranges for the formation of alloys with special structures have been predicted. The temperature–composition ranges for the formation of supersaturated solid solutions during liquid quenching have been evaluated.