Solid Solubility Extension Research Articles

Influence of Pre-Milling on the Mn Solid Solubility in the Al-Mn-Cu Alloy during Mechanical Alloying

Increasing the strength of Al-based alloys is an important issue of physical metallurgy and industrial processing. Severe plastic deformation and related extension of solid solubility during mechanical alloying provide an opportunity for significant strengthening due to grain refinement, solid solution, and precipitation strengthening mechanisms. During mechanical alloying, an anomalous increase in the solid-state solubility of alloying elements occurs. The present study focuses on the investigation of the pre-milling treatment to the microstructure, phase composition, and solubility in Al-7.7 Mn-3.5 Cu (wt%) alloy processed by a high-energy ball milling of Al-14.3 Mn-6.5 Cu (wt%) master alloy diluted with Al powder. During milling, the mean granular size decreased to ~5 µm, and a strong grain refinement occurred. According to our TEM and XRD data, ball milling provided a mean grain size of 13–14 nm and a microhardness of 490–540 HV. The lattice parameter of the Al-based solid solution decreased with an increase in the milling time to 7.5–10 h, which suggested the dissolution of the alloying elements, and the lattice parameter increased at a higher milling time of 12.5–40 h, which suggested the decomposition of the solid solution. The XRD data revealed the dissolution of the Al6Mn and Al20Cu2Mn3 solidification-originated phases with a further precipitation of the Al6Mn dispersoids. Pre-milling of the master alloy entailed a significant decrease in the minimal lattice parameter value from 0.4029 nm to 0.4023 nm due to an increase in the Mn solute content from 6.2 wt% (3.3 at%) to 7.5 wt % (4.0 at%) in the studied alloy during high-energy ball milling.

Thermodynamic analysis of nanocrystalline solid solutions formation in copper‐lead‐tin ternary immiscible system during mechanical alloying

AbstractIn this paper, copper‐15 wt.%‐lead‐1 wt.%‐tin (Cu‐15wt %Pb‐1wt %Sn), copper‐15 wt.%‐lead‐2 wt.%‐tin (Cu‐15wt %Pb‐2wt %Sn) and copper‐15 wt.%‐lead‐3 wt.%‐tin (Cu‐15wt %Pb‐3wt %Sn) powder mixtures were mechanically alloyed in order to study the solid solubility extension during the alloying process. Nanocrystalline supersaturated solid solutions have been prepared in copper‐lead‐tin (Cu−Pb−Sn) ternary immiscible system by mechanical alloying (MA). Based on the thermodynamic model, the Gibbs free energy changes in these alloys during the formation of solid solutions are calculated to be positive, which means that there are no driving force to form solid solutions in copper‐lead‐tin ternary immiscible system. It was found that a large fraction of grain boundaries and a high density of dislocations play a significant role in the solid solubility extension in copper‐lead‐tin ternary immiscible system.

Solid solubility extension and nano-mechanical properties of rapidly solidified Fe-Zr eutectic alloys under free fall condition

The liquid-solid phase transitions and solidified microstructures of highly undercooled Fe-Zr eutectic melts were investigated by the drop tube technique. The quantitative relationships among droplet diameter (D), undercooling (ΔT) and cooling rate (Rc) were calculated for three types of eutectic alloys (Fe-9.8 at. % Zr, Fe-6 at. % Zr and Fe-16 at. % Zr alloys). Furthermore, the evolutions of solidified microstructure with droplet diameter were studied. The results show that the eutectic microstructure for Fe-9.8 at. % Zr droplet transforms from regularly lamellar shape to anomalous shape as the diameter reduces. The α-Fe dendrite in Fe-6 at. % Zr droplet transforms from coarse dendrite to refined dendrite with the decrease of droplet diameter, while the Fe2Zr dendrite in Fe-16 at. % Zr droplet transforms from faceted dendrite to non-faceted grain. Besides, a remarkable solid solubility extension was found in both the α-Fe dendrites of Fe-6 at. % Zr alloy and the Fe2Zr dendrites of Fe-16 at. % Zr alloy. The solid solubility of the α-Fe dendrite increases from 3 at. % to 5.6 at. % when the droplet diameter reduces from 1069 to 212 µm, while it decreases from 31 to 22 at. % in the Fe2Zr dendrite as the diameter reduces from 991 to 228 µm. The microstructural morphology and solid solubility are directly related to the nano-hardness and Young’s elastic modulus of alloys. The nano-mechanical properties of the eutectic gradually increase with the refinement of the layers, and gradually decrease as the irregularity of the anomalous eutectic increases. With the reduction of droplet diameter, the nano-hardness rises and Young’s elastic modulus continuously diminishes for the α-Fe dendrite due to the increase in the solute content of Zr, while these two mechanical properties gradually decrease for the Fe2Zr dendrite because of the reduction in the solute content of Zr.

Thermodynamic analysis of the extension of solid solubility in copper‐lead immiscible system prepared by mechanical alloying

AbstractX‐ray diffraction analysis, scanning electron microscopy and thermodynamic calculations in the Miedema's model were used to study the extension of solid solubility in copper‐lead immiscible system prepared by mechanical alloying. The result shows that the nanocrystalline supersaturated solid solution formed during the alloying process. The Gibbs free energy change in this system during the formation of solid solution is calculated and shows to be positive, which means that a thermodynamic barrier exists for the formation of this alloy system in solid state. It has been found that the additional energy stored in nanocrystalline copper‐lead alloy during the alloying process as a result of crystallite size reduction and increased dislocation density, would be high enough to overcome the thermodynamic barrier in the formation of a solid solution.

Extension of Solid Solubility and Structural Evolution in Nano-Structured Cu-Cr Solid Solution Induced by High-Energy Milling

In Cu-Cr alloys, the strengthening effects of Cr are severely limited due to the relatively low Cr solid solubility in Cu matrix. In addition, apart from the dissolved Cr, it should be noted that high proportion of Cr in Cu matrix work as the second phase dispersion strengthening. Therefore, it is of great significance to extend the Cr solid solubility and decrease the size of the undissolved Cr phase to nano-structure. In this work, the nano-sized Cu-5 wt.% Cr solid solution was achieved through high energy ball milling (HEBM) only for 12 h. The Cr solubility of ~1.15 at.% was quantitatively calculated based on XRD patterns, which means supersaturated solid solution was realized. Except for the dissolved Cr, the undissolved Cr phase was with nano-sized work as the second phase. Upon milling of the Cu-Cr powders with coarse grains, the crystallite sizes and grain sizes are found to decrease with the milling time, and remain almost unchanged at a steady-state with continued milling. In addition, it was found that the stored energy induced by dislocation density increment and grain size refinement would be high enough to overcome the thermodynamic barrier for the formation of solid solution.

On the Solid Solubility Extension by Rapid Quenching and Spinodal Decomposition during Aging in Melt-Spun Cu–Ti Alloys

On the Solid Solubility Extension by Rapid Quenching and Spinodal Decomposition during Aging in Melt-Spun Cu–Ti Alloys

Characterization investigations of the mechanically alloyed and sequentially milled Al-12.6 wt.% Si eutectic alloy powders

This study reports on the detailed microstructural characterization of Al-12.6 wt.% Si eutectic alloy powders synthesized from Al and Si elemental starting materials via mechanical alloying (MA) for 4, 6, and 8 h, and subsequent cryomilling (CM). Mechanically alloyed (MA’d) powders were cryomilled (CM’d) for 10, 20, and 30 min in a freezer/mill using liquid N2 gas circulated externally around the polycarbonate milling vial containing stainless steel rods. SEM/EDS and TEM/EDS mapping analyses revealed the presence of some Si embedded in the Al-rich particles and some existed as free Si. As expected, with increasing MA and sequential milling (MA + CM) duration, strain values increased and crystallite sizes decreased. Si solubility in α-Al was enhanced with increasing MA durations and utilizing MA and CM consecutively (sequential milling) as indicated by DSC endothermic and XRD peak shifts. A maximum solubility of 2.25 at.% Si in α-Al or Si solid solubility extension of 0.65 at.% was estimated for the Al12.6Si eutectic alloy powders MA’d for 8 h.

Selection of grain-boundary segregation elements for achieving stable and strong nanocrystalline Mg

Nanocrystalline metals, e.g., Mg, are often strong but with a low thermal stability. In this study, six solute elements, Ti, Zr, Ta, Co, Cr, La, which are immiscible in Mg under equilibrium conditions, are mechanically alloyed with Mg to study the extension of solid solubility, the thermal stability and the mechanical properties of nanocrystalline Mg. Extended solid solubility of Ti and Zr solutes in Mg matrix is achieved after mechanical alloying. The nanocrystalline Mg is largely stabilized by Ti, moderately stabilized by Zr, and not stabilized by Ta, Co, Cr and La. The onset temperature for a rapid grain growth increases from 100°C (0.4 Tm) for nanocrystalline Mg to ~ 350°C (0.68 Tm) for nanocrystalline Mg0.95Ti0.05 (defined as Mg-5Ti). A relatively small grain size of ~ 145nm is achieved in Mg-5Ti at 350°C. The enhanced thermal stability of nanocrystalline Mg-Ti alloy can be attributed to the segregation of Ti atoms at grain boundaries. In addition, an abnormal grain growth is also observed because of the inhomogeneous distribution of solute/impurity atoms. The high thermal stability of nanocrystalline Mg-5Ti alloy enables us to degass the mechanically alloyed powders at a high temperature of 300°C and achieve a porosity-free nanocrystalline bulk with a compressive yield strength of 183MPa and a fracture strain of above 0.6.

Solid solubility extension of copper‐tin immiscible system during mechanical alloying

AbstractIn this paper, copper‐5 wt.%‐tin (Cu‐5wt%Sn) powder mixture was mechanically alloyed in order to study the solid solubility extension during the alloying process. Nanocrystalline supersaturated solid solution has been prepared in this system by high energy ball milling. Based on the thermodynamic model, the Gibbs free energy change in this alloy system during the formation of solid solution is calculated to be positive, which means that there is no driving force to form solid solution in copper‐tin (Cu−Sn) immiscible system. It has been found that a large fraction of grain boundaries and a high density of dislocations play a significant role in the solid solubility extension of immiscible copper and tin.

Effect of ball milling on the ageing response of Al2618 composites reinforced with SiC and oxide nanoparticles

High-energy ball milling was carried out to disperse SiC nanoparticles (ex-situ reinforcement) and fragments of oxide (in-situ reinforcement) in an Al2618 alloy matrix. Nanocomposite powders were consolidated by hot rolling at 600 °C. Samples produced using ball milled powder showed a weak response to ageing treatment as demonstrated by thermal and microstructural analyses and by hardness tests. Repeated plastic deformation of powder induced by ball milling led to high density of crystal defects which are believed to be responsible of an extension of solid solubility, thus reducing the driving force for precipitation during ageing. Tensile tests were performed at room temperature and at 120 °C on solution treated and peak-aged samples. The nanocomposites showed a remarkably high yield strength and an impressive ability in keeping high mechanical properties even at high temperature. Serrations were noticeable in stress-strain curves both before and after ageing, which are ascribed to the dynamic strain ageing mechanism.

Effect of zirconium on thermal stability of nanocrystalline aluminium alloy prepared by mechanical alloying

In the present study, a series of Al-x% Zr (x = 1–10 at.%) compositions were prepared by mechanical alloying (MA) to investigate the solid solubility extension of Zr in Al and its thermal stability. The elemental powder blends were mechanically alloyed under high purity argon atmosphere in stainless steel grinding media using SPEX 8000 M high energy ball mill. The milling was carried out for 8 h at room temperature and the ball to powder ratio was maintained at 10:1. Formation of disordered solid solutions is validated using Miedema’s semi-empirical model. X-ray diffraction (XRD) analysis confirms the formation of disordered solid solution up to 1at.% Zr; whereas, Al3Zr and Al9.83Zr0.17 intermetallic phases were found to form as per the XRD pattern of 2–10% Zr alloys. Variation of lattice parameter confirmed the formation of Al-1% Zr solid solution. Crystallite size was estimated to be 41 and 30 nm, respectively, for the as-milled 1 and 10% Zr alloys. The matrix grains were found to be stabilized after annealing at 550 °C, and the XRD crystallite size of Al-10% Zr retained at ∼58 nm. TEM and AFM analysis confirmed that the grain size of the as-milled as well as annealed samples was retained in the nanometre range (<100 nm), which corroborates well with the XRD crystallite size. Vickers microhardness of the as-milled 10% Zr alloy was found to be 2.4 GPa, which decreased to 1.7 GPa after annealing at 550 °C. This demonstrated that the dissolution of Zr in Al has a larger strengthening effect and Zr plausibly played a pivotal role in retaining the matrix grains size in the nanoscale range at high temperature.

Solid solubility extension and microstructure evolution of cast zirconium yttrium alloy

Yttrium addition can improve the oxidation resistance, mitigate hydrogen embrittlement and thus enhance the mechanical properties of the zirconium alloy. To study solid solubility extension of yttrium in zirconium alloy, the lattice parameters of α-Zr phase in Zr–Y alloy were accurately determined by X-ray diffraction (XRD). Yttrium exhibits solid solubility extension in the cast zirconium alloy which forms a metastable supersaturated solid solution with solubility limit of around 3 wt%. The effect of yttrium and thermal treatment on the microstructure of the alloys was investigated by optical microscopy (OM) and scanning electron microscope (SEM). The cast Zr–Y alloy shows a normal polycrystalline structure with dispersed α-Y particles when Y content is lower than 4 wt%, while the alloy shows a eutectic structure with dendrites formation when the Y content is higher. Yttrium exhibits a strong grain refining effect on zirconium alloy and precipitates from the metastable supersaturated Zr matrix after annealing at 700 and 900 °C.

Effects of Mechanical Alloying on Solid Solubility

Mechanical alloying (MA) is a potential processing method for various equilibrium and non-equilibrium alloy phases such as supersaturated solid solution, metastable crystalline, amorphous, quasi-crystalline phases, nanostructures. Compared to conventional high temperature material processing such as melting and casting, improvement of solid solubility limit results from mechanical alloying at room temperature. The solid solubility increases with increase in milling time due to enhanced stress assisted atomic diffusion during particle refinement and reaches a saturation level at higher milling time. The extension of solid solubility is attributed to thermodynamic, dynamic or kinetic factors such as high dislocation density due to severe plastic deformation during particle refinement and enhanced diffusivity during MA. The review aims to discuss the insight of MA than other non-equilibrium processing in terms of achieving higher solubility, reasoning and mechanism of solubility improvement during MA of different alloy systems.

Experimental study of the crystal structure of the Mg15−xZnxSr3 ternary solid solution in the Mg–Zn–Sr system at 300°C

Abstract A new ternary compound, Mg 15 − x Zn x Sr 3 with extensive solid solubility in the Mg–Zn–Sr system was observed and studied using electron probe microanalysis (EPMA), scanning electron microscopy SEM, and X-ray techniques. The solid solubility limits of this compound were found to be Mg 15 − x Zn x Sr 3 (0.24 ≤ x ≤ 10.58, at.%) at 300 °C using a diffusion couple and several equilibrated alloys. Analysis of the X-ray diffraction (XRD) patterns was carried out by Rietveld method. XRD data has shown that this solid solution crystallizes in the hexagonal P6 3 /mmc (194) space group with the Ni 11 Si 4 Sc 3 prototype. The lattice parameters decrease linearly with decreasing Mg content indicating substitutional solid solubility. The fractional atomic occupancy of the 6h, 6g, 4f, 2b and 12k sites of this compound are function of Mg content.

An investigation on morphology and structure of Cu–Cr alloy powders prepared by mechanical milling and alloying

A method combined with mechanical milling (MM) and mechanical alloying (MA) was performed to prepare nanocrystal Cu–Cr supersaturated solid solution from commercially available powders. Cu and Cr powders were pre-milled separately by MM for 20h, and then mechanically alloyed with as-received Cr and Cu powders respectively in a wet condition for 100h. The morphology and structure of the samples were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique respectively. Compared with MA without pre-milling and pre-milling of Cu, MA of pre-milled Cr and as-received Cu mixtures could produce finer alloy powders with higher powder yield, narrower range of size distribution, smaller crystallite size and higher dissolution of Cr, which will show desirable properties after subsequent consolidation and present an attractive potential for technological applications. The mechanical alloying mechanisms including morphological changes, crystallite refinement and solid solubility extension were discussed to explain the phenomena during the fabrication process.

Investigation on solid solubility and physical properties of Cu–Fe/CNT nano-composite prepared via mechanical alloying route

Mechanical alloying was utilized to produce Cu80Fe20/CNT nano-composite powder. The effects of CNT addition on solid solubility of Fe in Cu, morphology, magnetic, and electrical properties of the products were evaluated using X-ray diffraction, field emission scanning electron microscopy, vibrating sample magnetometer, and four point probe technique, respectively. It was found that solid solubility of Fe in Cu increased to 20wt.% in a sample milled for 15h, but CNTs impeded the solid solubility extension in Cu80Fe20/CNT nano-composites. CNTs were distributed evenly in metal matrix after 15h mechanical alloying and final products were agglomerates consisting of nano-particles. Analysis of magnetic hysteresis loops showed that the magnetic properties of nano-composite samples were altered as a function of CNT addition. Saturation magnetization and coercivity of composite samples increased with increasing CNT content probably due to the presence of non-dissolved Fe in nano-composites and exchange coupling phenomenon, respectively. Electrical resistivity of nano-composites also increased with increasing CNT concentration.

Effect of milling energy on preparation of nano-structured Fe70Si30 alloys

In this paper, the effect of milling energy on solid solubility extension of Si in Fe was studied. Ball-milling experiments were conducted under different conditions such as rotation speed, ball-to-powder weight ratio and milling time. The phase composition, morphology and magnetic properties of nano-structured alloy powders were analyzed by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer techniques, respectively. The milling energy was calculated by using the collision model. A total energy of about 31.9kJ/g was necessary for solid solution formation. A comparison between formation enthalpy and total energy of grinding balls was also done. Results showed that the efficiency factor was about 1.4%. It was also found that the phase evolution in this system is closely related to the milling energy. The impact energy has a significant effect on morphology, crystallite size and lattice strain. The crystallite size of the Fe–Si (α) phase decreased up to 15nm and the particle size reached to 100nm under the given experimental conditions.

Microstructure and Microhardness Evolutions of High Fe Containing Near-Eutectic Al-Si Rapidly Solidified Alloy

Al-11 wt.% Si-11 wt.% Fe (11.29 at.% Si-5.6 at.% Fe) melt was rapidly solidified into ribbons and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and microhardness technique. The Rietveld X-ray diffraction analysis was applied successfully to analyze microstructure and phase precipitations. On the basis of the aluminum peak shifts measured in the XRD scans, a solid solubility extension value of 1 at.% Si in α-Al was determined. SEM investigations confirmed presence of a spherical shape α-phase particles in addition to needle and spherical shape β-phase particles with contents of 1.1 wt.% and 10.1 wt.% as deduced by XRD analysis. During prolonged annealing process at 350°C/25 h, α-phase disappeared, β-phase content increased to 30 wt.%, and Si presence becomes more evident as deduced by XRD analysis. EDS analysis confirmed that these β particles observed in the as-melt spun alloy are of lower Fe content comparing to those usually observed in the as-cast counter-part alloy. Besides, the length distribution of needle shape β-particles has been shortened to be diverse from 1 to 5 μm. The as-melt spun ribbons exhibited enhancement of hardness to 277 HV and further increased during heat treatment (150°C/12 h) to 450 HV. This improvement of microstructure and hardness are the influence of microstructural refinement and modification obtained during the rapid solidification process.

Fabrication of nanocrystalline alloys Cu–Cr–Mo super satured solid solution by mechanical alloying

This work discusses the extension of solid solubility of Cr and Mo in Cu processed by mechanical alloying. Three alloys processed, Cu–5Cr–5Mo, Cu–10Cr–10Mo and Cu–15Cr–15Mo (weight%) using a SPEX mill. Gibbs free energy of mixing values 10, 15 and 20 kJ mol−1 were calculated for these three alloys respectively by using the Miedema's model. The crystallite size decreases and dislocation density increases when the milling time increases, so Gibbs free energy storage in powders increases by the presence of crystalline defects. The energy produced by crystallite boundaries and strain dislocations were estimated and compared with Gibbs free energy of mixing values. The energy storage values by the presence of crystalline defects were higher than Gibbs free energy of mixing at 120 h for Cu–5Cr–5Mo, 130 h for Cu–10Cr–10Mo and 150 h for Cu–15Cr–15Mo. During milling, crystalline defects are produced that increases the Gibbs free energy storage and thus the Gibbs free energy curves are moved upwards and hence the solubility limit changes. Therefore, the three alloys form solid solutions after these milling time, which are supported with the XRD results.

Microstructure and microhardness evolution of melt-spun Al-Si-Cu alloy

Al-11 wt.% Si-11 wt.% Cu (11.29 at.% Si-5.1 at.% Cu) melt was rapidly solidified into ribbons and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and microhardness technique. The Rietveld X-ray diffraction analysis was applied successfully to analyze the microstructure and phase precipitations. The high cooling rate obtained in rapid solidification has a significant influence on the microstructure and microhardness of this alloy. On the basis of the Al peaks shift measured in the XRD scans, a solid solubility extension value of 3.95 at.% Si and 3.54 at.% Cu in α-Al were determined. No XRD peaks of the Si phase have been detected. XRD peaks of the intermetallic Al2Cu phase have been observed clearly with estimated content of 12.6 wt.%. During prolonged annealing process at 350°C/25 h, XRD peaks of the Si phase clearly appeared with estimated content of 8.6 wt.% and, moreover, the Al2Cu phase content increased to 16 wt.%. The estimated crystallite size and micro-strain % of α-Al are 30 nm and 0.056, respectively. The melt-spun wheel side ribbon represents ultra-fine microstructure with particles size less than 1μm and exhibits enhancement of hardness to 241 HV. Hardness has further increased to 291 HV during heat treatment (150°C/12 h). Rapid solidification exhibited a great influence on microstructure and microhardness of the Al-Si-Cu alloy.