Crystals Of Intermetallic Compounds Research Articles

Investigating the influence of rotating magnetic field (RMF) on intermetallic compound crystallization, thermal and mechanical properties in lead-free Sn-Ag-Cu solder alloys during solidification

This research delves into the effectiveness of using rotating magnetic field (RMF) during the solidification process of Sn-3.5 wt% Ag-0.7 wt% Cu (SAC 357) alloy. The main goal is to evaluate the effect of RMF on the crystallization of intermetallic compounds (IMCs), as well as to study its implications for the thermal properties and creep resistance of the resulting alloy. It is found that the application of the RMF has a significant promotion effect on the improvement in the grain structure of the primary AgSn phase within the directionally solidified SAC 357 alloy. With the application of RMF, the morphology of the primary AgSn phase transformed from developed dendritic-like to fine needle-like, accompanied by a decrease in grain size, but shows no discernible impact on their composition. This observation is attributed to the influence of Lorentz force and thermo-electromagnetic convection. The implementation of a rotating magnetic field (RMF) resulted in notable enhancements in the thermal properties of the SAC357 solder alloy. Specifically, RMF application led to reductions in both the pasty range and melting temperatures, accompanied by a decrease in undercooling compared to conditions without stirring.The SAC357 alloy, when modified with a magnetic field, demonstrated the longest creep rupture time and higher creep resistance compared to those not subjected to magnetic field modification. This research endeavor aims to address a notable gap in our understanding concerning the behavior of SAC357 solder alloys when subjected to a Rotating Magnetic Field (RMF).

Thermodynamic Modeling of Formation Enthalpies of Amorphous and Crystalline Phases in Zr, Nd, and Ce-Substituted Fe-Si Systems

The alloys that crystallize in a tetragonal ThMn12-type (space group I4/mmm) structure and are based on Fe and rare earth elements are believed to have a potential to plug the performance gap between ferrite and Nd-based magnets. Nevertheless, the progress is hindered by their poor structural stability, compared with other phases competing during the synthesis process, e.g., Th2Zn17-type. In this work, the enthalpies of the formation (and other thermodynamic parameters) of various phases in (Zr, Nd, Ce)-Fe-Si systems were calculated, with paramount focus on the Fe-rich compositions. We compared and discussed the stability range and stabilization routes for amorphous phases, solid solutions, and intermetallics. The beneficial influence of Zr and Si on the crystallization of intermetallic compounds was confirmed, simultaneously being valid for other phases. Among all of the analyzed Fe-rich phases, the lowest values for enthalpy of the formation of the amorphous phase and solid solution were determined for ZrFe10Si2 (−17.5 and −18.2 kJ/mol, respectively). Moreover, substitution by elements with a large atomic radius is indicated as a method for the introduction of topological disorder, giving possibility for the synthesis of metastable phases (even amorphous) and the utilization of more sophisticated synthesis routes in the future.

Regulating the crystal structure of layered double hydroxide-derived Co-In catalysts for highly selective CO2 hydrogenation to methanol

Highly selective CO2 hydrogenation faces a significant technological challenge, though many efforts have been made on this subject. Herein, Co-In catalyst with excellent structure was synthesized from layered double hydroxides, and its crystal structures were regulated by H2 reduction for selective CO2 hydrogenation to methanol. As reduction temperature increases, In2O3 crystals are destroyed by degrees, resulting in gradual loss of CO2 adsorption on oxygen vacancies, but more CoIn2 intermetallic compound crystals are generated, which can serve as new active phases to adsorb and activate CO2. Density functional theory calculations show that newly-formed CoIn2 crystals are more inclined to convert massive CO2 to formate intermediate and improve CH3OH selectivity significantly. The CoInLDH catalyst reduced at 350 °C with relatively intact In2O3 crystals and plentiful CoIn2 crystals shows high catalytic performance with CO2 conversion of 13.8% and CH3OH selectivity of 83.7%. This work provides a valuable insight into improving CO2 hydrogenation by catalyst crystal regulation.

X-ray Imaging of Alloy Solidification: Crystal Formation, Growth, Instability and Defects.

Synchrotron and laboratory-based X-ray imaging techniques have been increasingly used for in situ investigations of alloy solidification and other metal processes. Several reviews have been published in recent years that have focused on the development of in situ X-ray imaging techniques for metal solidification studies. Instead, this work provides a comprehensive review of knowledge provided by in situ X-ray imaging for improved understanding of solidification theories and emerging metal processing technologies. We first review insights related to crystal nucleation and growth mechanisms gained by in situ X-ray imaging, including solute suppressed nucleation theory of -Al and intermetallic compound crystals, dendritic growth of -Al and the twin plane re-entrant growth mechanism of faceted Fe-rich intermetallics. Second, we discuss the contribution of in situ X-ray studies in understanding microstructural instability, including dendrite fragmentation induced by solute-driven, dendrite root re-melting, instability of a planar solid/liquid interface, the cellular-to-dendritic transition and the columnar-to-equiaxed transition. Third, we review investigations of defect formation mechanisms during near-equilibrium solidification, including porosity and hot tear formation, and the associated liquid metal flow. Then, we discuss how X-ray imaging is being applied to the understanding and development of emerging metal processes that operate further from equilibrium, such as additive manufacturing. Finally, the outlook for future research opportunities and challenges is presented.

Nucleation bursts of primary intermetallic crystals in a liquid Al alloy studied using in situ synchrotron X-ray radiography

The nucleation of primary Pt-rich intermetallic compound (IMC) crystals was studied in a model Al-Pt-Er alloy as an analogue to Al13Fe4 that forms in commercial Al alloys. The Pt-rich IMCs provided strong X-ray absorption contrast that allowed earlier detection of formation events and the resolution of solute diffusion fields. Crystal formation behaviour was investigated during directional and isothermal solidification when the alloy was inoculated with TiB2 particles at cooling rates of 0.1 Ks−1 to 8 Ks−1 using in situ synchrotron X-ray radiography. Different from previous studies that concerned disordered, solid solution phases such as α-Al dendrites, for the first time nucleation bursts of ordered compound crystals were observed, where the nucleation of the IMC crystals proceeded in distinct cascades (in the time domain) or waves (in the spatial domain), the magnitude of which increased with increasing cooling rate and particularly with decreasing thermal gradient in the melt. Comparing the crystal number density with the estimated number density of TiB2 particles suggested that the IMC crystals nucleated only on the most potent TiB2 particles, accounting for ∼0.5% of the total TiB2 number density in the melt. The effect of the thermal gradient and cooling rate on the magnitude of the nucleation waves and the IMC number density was revealed in terms of the available undercooling in the liquid in front of an individual IMC and the solute depleted liquid fraction that arose from the interaction of an ensemble of IMC crystals.

In-situ X-ray radiography of primary Fe-rich intermetallic compound formation

The formation of primary Fe-rich intermetallic compound crystals and the effect of TiB2 and TiC inoculation during solidification of a hypereutectic Al-Fe alloy has been investigated. Both horizontal, near isothermal conditions and vertical, directional thermal gradient conditions were studied using laboratory and synchrotron X-ray radiography. TiB2 and TiC inoculation enhanced formation of Fe-rich intermetallics under all experimental conditions. Near isothermal solidification resulted in the highest intermetallic number density and average formation rate, whilst increasing the thermal gradient reduced both. A model for intermetallic crystal formation is proposed to explain the effect of thermal gradient and cooling rate on the intermetallic number density and average formation rate.

Velocity measurements in the liquid metal flow driven by a two-phase inductor

We present the results of velocity measurements obtained by ultrasonic Doppler velocimetry and local potential probes in the flow of GaInSn eutectic melt driven by a two-phase inductor in a cylindrical container. This type of flow is expected in a recent modification to the floating zone technique for the growth of small-diameter single intermetallic compound crystals. We show that the flow structure can be changed from the typical two toroidal vortices to a single vortex by increasing the phase shift between the currents in the two coils from 0° to 90°. The latter configuration is thought to be favourable for the growth of single crystals. The flow is also computed numerically, and a reasonable agreement with the experimental results is found. The obtained results may be useful for the design of combined two-phase electromagnetic stirrers and induction heaters for metal or semiconductor melts.

ChemInform Abstract: Physical Properties of Single‐Crystalline Magnetic Intermetallic Compounds

AbstractReview: 43 refs.

First-principles density functional calculation of mechanical, thermodynamic and electronic properties of CuIn and Cu2In crystals

The study aims at assessing the mechanical, thermodynamic and electronic properties of single-crystalline and polycrystalline CuIn and Cu2In intermetallic compound (IMC) crystals using first-principles calculation based on the density functional theory within the generalized gradient approximation. The lattice constants and the five independent elastic constants of the two hexagonal single crystal structures are first calculated as a function of hydrostatic pressure, and their elastic anisotropy is examined through the computation of the crystal direction-dependent elastic modulus and the Zener anisotropy factor. Subsequently, their associated pressure-dependent polycrystalline elastic properties are also predicted, by which the ductility or brittleness of the IMC materials is characterized. Moreover, the temperature-dependent Debye temperature and heat capacity of these two IMC nanocrystals are determined using a quasi-harmonic Debye model, and their electronic band structures and density of states profiles are examined through analysis of electronic characteristics.The calculation results show that these two IMC crystals are not only an elastically anisotropic, low stiff and very ductile material but also a conductor. The elastic anisotropy, Debye temperature and heat capacity of Cu2In single crystal all surpass those of CuIn, and also, Cu2In crystal tends to be much stiffer than CuIn. Besides, the heat capacity of these two nanocrystals strictly follows with the well-known T3-law at temperature below the Debye temperature and would reach the Dulong–Petit limit at temperature above the Debye temperature.

Ultra-high vacuum compatible image furnace

We report the design of an optical floating-zone furnace for single-crystal growth under ultra-high vacuum (UHV) compatible conditions. The system is based on a commercial image furnace, which has been refurbished to be all-metal sealed. Major changes concern the use of UHV rotary feedthroughs and bespoke quartz-metal seals with metal-O-rings at the lamp stage. As a consequence, the procedure of assembling the furnace for crystal growth is changed completely. Bespoke heating jackets permit to bake the system. For compounds with elevated vapor pressures, the ultra-high vacuum serves as a precondition for the use of a high-purity argon atmosphere up to 10 bar. In the ferromagnetic Heusler compound Cu(2)MnAl, the improvements of purity result in an improved stability of the molten zone, grain selection, and, hence, single-crystal growth. Similar improvements are observed in traveling-solvent floating-zone growth of the antiferromagnetic Heusler compound Mn(3)Si. These improvements underscore the great potential of optical float-zoning for the growth of high-purity single crystals of intermetallic compounds.

Physical properties of single‐crystalline magnetic intermetallic compounds

AbstractSingle crystals on a macroscopic scale exhibit microscopic periodicity on an atomic level, which enables us to investigate their intrinsic physical properties and to optimize their functional properties. We have grown various kinds of magnetic single crystals of intermetallic compounds for fundamental research and for applications. In this, much effort has been focused on the growth conditions to satisfy the different requirements, especially for crystals that are hard to grow. In this paper, we review some selected results on various single crystals grown in our institute and illustrate the importance of single‐crystal growth for research and application. Several intrinsic magnetic properties, including magnetocrystallographic anisotropy, spin reorientations, and magnetostriction have been investigated in detail on single crystals of rare‐earth intermetallic compounds. The internal stress induced in crystals of magnetic shape‐memory alloys is utilized to reorient the martensitic microstructure for maximizing the output strain. Combining the self‐flux method with magnetic elevating Czochraski cold‐crucible growth technology, a deeply undercooled environment was achieved to enable (Tb,Dy)Fe2 single crystals to be grown. Some research works on crystal growth, such as solidifying theories, growth dynamics, and phase diagrams, are also discussed.

Ninetieth anniversary of Czochralski method

In 2006 we celebrate the 90th anniversary of the Czochralski pulling method. Professor Jan Czochralski invented this method and used it for measuring of the crystallization velocity of metals. In the 1950s of the 20th century his method was adopted for growing large single crystals of semiconductors on an industrial scale. Moreover, large group of applicable crystals, e.g. oxides is grown using Czochralski method. Also the number of the single crystals of intermetallic compounds is quickly growing thanks to this method.

Edge effects in intermetallic compound crystal growth between Nb and molten 52In–48Sn solder

A solder/substrate couple consisting of a Nb substrate and eutectic 52In–48Sn solder shows promise for high-temperature liquid solder interconnects. In this letter, the intermetallic compound (IMC) crystal growth between vacuum-sputtered Nb film and molten 52In–48Sn solder at four temperatures; 192, 220, 240, and 260°C, was investigated employing samples with a solder/substrate interface area of 7mm by 7mm. It was found that at all four temperatures, the IMC crystals nucleated and grew first at the corners of the substrate, followed by the edges, and then gradually covered the entire interface. This result, can be explained if the initiation of IMC crystal growth is diffusion controlled, and the value of the Nb diffusion coefficient is estimated with the aid of a three-dimensional numerical simulation.

Characterization of Intermetallic Compound Layer Formed at the Weld Interface of the Defocused Laser Welded Low Carbon Steel/6111 Aluminum Alloy Lap Joint

Lap joining of the low carbon steel (SPCC: Steel Plate Cold-rolled C) and aluminum alloy 6111-T4 plates was carried out using a defocused YAG laser beam. Precise TEM and TEM-EDX analyses were performed for the intermetallic compound (IMC) layer formed at the welding interface of the lap joint, which was fabricated under the following conditions: (laser power: 3.0 kW, defocus distance: 20 mm, laser traveling speed: 2.17 x 10 -2 ms -1 ). The IMC layer consisted of very fine granular crystals. The fine IMC crystals with about 500 nm in diameter formed at the interface between IMC layer and solidified A6111 region. In contrast, IMC crystal grains at the central region of the layer were relatively large and the average size was 1 μm. Both TEM-EDX and electron diffraction pattern analyses confirmed that the former is Al 13 Fe 4 and the latter is Al 5 Fe 2 . The greater part of the IMC layer was occupied by Al 5 Fe 2 in the present welding condition. Another ultra fine IMC grains were observed at the interface between the SPCC and IMC layer. The electron diffraction pattern analysis revealed that they were FeAl, Fe 3 Al and Al 6 Fe.

Ammonothermal Crystal Growth of Germanium and Its Alloys: Synthesis of a Hollow Metallic Crystal

Elemental germanium and other metals, including Cu, In, Ag, Bi, Sn, and In, are transported under acidic ammonothermal conditions from the hot zone of a sealed quartz tube to the cool zone, where both crystalline and amorphous materials can deposit. Red amorphous Ge deposits when finely divided Ge that is covered with surface oxide is used along with NH4Br mineralizer. When the Ge feedstock is mixed with other metals or metal salts prior to heating, crystals of intermetallic compounds can be grown. Hexagonal crystals of a Cu−Sn−Ge alloy, Cu3Ge, [Sn6O8Ge(NH3)]n, and unusual hollow crystals of a Ag−Sn−Ge alloy were obtained from these reactions.

Single-crystal growth of Tb 0.4Y 0.6Ni 2B 2C compounds by the floating-zone method

Single crystals of a Tb 0.4Y 0.6Ni 2B 2C intermetallic compound, which exhibit the coexistence of superconductivity and low-temperature magnetic ordering, have been grown by vertical floating-zone melting. The growth process of these intermetallic compound crystals is analysed from in situ tracking of the zone temperature, segregation behaviour along the axis, and the constitution of the ultimate zone. The slight shift of composition along the crystal axis, increase in Tb/(Tb+Y)-fraction but decrease in Ni/B ratio, were revealed by electron probe microanalysis. The superconducting transition temperature along the axis co-ordinate is nearly constant at T c=4.0±0.1 K with a transition range of Δ T c=0.8 K. Stacking faults resulting from a local deviation of the stoichiometric composition were found near the end of the crystal by TEM investigations.

The forming mechanism of ultradispersed phases in rapidly solidified aluminium alloys

The effects of crystallization conditions (melt heating temperature and cooling rate) on the size and morphology of ultradispersed crystals of intermetallic compounds are considered. Insight into the metastable colloid state of the melt makes it possible to perform the qualitative transformations of the crystal structure of the alloys obtained by rapid quenching from various temperatures.

The new chimney-ladder phases Co 2Si 3 and Re 4Ge 7 formed by treatment at high temperatures and pressures

The crystallization of intermetallic compounds in the Co-Si and Re-Ge systems was investigated at high pressures and temperatures. Two new phases, Co 2Si 3 and Re 4Ge 7, were found, both of which are Nowotny chimney-ladder structures. The Co 2Si 3 phase has the Ru 2Sn 3-type structure and a tetragonal unit cell with parameters a = 5.234 ± 0.003 A ̊ and c = 8.543 ± 0.005 A ̊ which contains four molecules. The Re 4Ge 7 phase has the Tc 4Si 7-type structure and a tetragonal unit cell with a = 5.895 ± 0.004 A ̊ and c = 18.86 ± 0.01 A ̊ which also contains four molecules.

Growth of single crystals of intermetallic compounds of niobium with germanium and gallium by chemical transport method

Growth of single crystals of intermetallic compounds of niobium with germanium and gallium by chemical transport method