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• Mg element contributes to the breakage of the oxide films on the surfaces of the Ti and Al–Mg alloy powders. • Changes in the Mg content of the liquid phase during heating affect the formation and phase transformation of the reaction products. • The Al 18 Ti 2 Mg 3 reaction layer fractures more easily than the Al 3 Ti layer. • The reduced solid-liquid interfacial energy leads to the Al 3 Ti particles changing from blocky shape to plate-like form with the increased Mg content. • Al 18 Ti 2 Mg 3 particles grow through a twin plane re-entrant mechanism. The reactions between Ti and Al–Mg alloys were systematically investigated by heating the Ti/Al–Mg alloy powder mixture compacts with Mg contents ranging from 5.09 to 40.36 wt.% at 660 °C. Mg element in the Al–Mg alloys contributed to the breakage of the oxide films on the surfaces of the Ti and Al–Mg alloy powders, thus, promoting the reactions. In the samples with Mg contents varying from 5.09 wt.% to 25.93 wt.%, the first-formed intermetallic compound was Al 18 Ti 2 Mg 3 , and then Al 3 Ti generated at the Al 18 Ti 2 Mg 3 /Ti interface. Since the Mg content in the Al–Mg melts decreased during the subsequent heating process, the previously formed Al 18 Ti 2 Mg 3 in the Ti/Al–5.09Mg sample transformed into Al 3 Ti accompanied by the reaction of Al with Ti to newly form Al 3 Ti, generating a single Al 3 Ti phase. In contrast, the new formation of Al 3 Ti and its transformation to Al 18 Ti 2 Mg 3 proceeded continuously in the Ti/Al–13.54Mg and Ti/Al–25.94Mg samples, resulting in a mixture of Al 18 Ti 2 Mg 3 and a little Al 3 Ti residue. In the Ti/Al–40.54Mg sample, Al 3 Ti was the unique reaction product throughout the heating process. The final Al 3 Ti particles in the Ti/Al–5.09Mg sample were in a blocky shape, while they were in a plate-like form in the Ti/Al–40.54Mg sample, which was caused by the enhanced growth anisotropy due to the decreased interfacial energy between Al 3 Ti particles and Al–Mg melts with the increase of Mg content. A twin plane re-entrant mechanism was suggested for the growth of Al 18 Ti 2 Mg 3 particles, weakening the anisotropic growth caused by the directional supply of Ti atoms, and contributing to the blocky morphology of Al 18 Ti 2 Mg 3 particles. In addition, the volume difference between the formed Al 18 Ti 2 Mg 3 and consumed Ti was greater than that between the Al 3 Ti and Ti, and the Al 18 Ti 2 Mg 3 has worse plasticity than the Al 3 Ti, resulting in the Al 18 Ti 2 Mg 3 reaction product fracturing more easily during thickening, thus forming a petal-like structure, but the Al 3 Ti product being in an almost continuous layer. [Display omitted] [ABSTRACT FROM AUTHOR]

• Coherent interface between Ni 2 Si and Cu induce plastic deformation of Ni 2 Si. • Every ISFE has lower value than that of atomic bond breaking energy during slip. • The super-coherency forms a number of new interfaces. • Lattice tilting and poly-crystallization operate to release the strain on Ni 2 Si. The intermetallic compound such as Ni 2 Si has a brittle nature. Therefore, monolithic intermetallic compounds have not yet been prepared by mechanical downsizing. During mechanical drawing of bulk Cu-Ni 2 Si alloy at room temperature, we observed more than 400% plastic elongation of hard and brittle Ni 2 Si intermetallic nano-fibers. The calculation based on the density functional theory reveals that the fully coherent interface induces strain on the intermetallic compound surrounded by the matrix, and lowers the intrinsic stacking fault energy below the level required to break an interatomic bond. The new interface between the Ni 2 Si intermetallic and Cu matrix formed by the plastic deformation is as stable as the original coherent interface formed by precipitation, and the activation energy of the newly formed interface to slip is similar to that of the Cu matrix. All of these make plastic deformation of brittle Ni 2 Si intermetallic possible by slip without failure. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new intermetallic compound of thermodynamically stable Nb2Ni phase is discovered within Nb-Ni binary system. • The strcture of Nb2Ni phase is determined to be the crystallographic FCC structure (Pearson: cF96, space grope: Fd-3m O2, a = 11.888 Å), which is confirmed by transmission electron microscopy. • The Nb2Ni phase is generated from the peritectoid transition: (Nb) + Nb7Ni6 → Nb2Ni, and the transformation temperature is 1533 K. • The equilibrium properties of Nb2Ni phase are produced by density functional theory. A new intermetallic compound of thermodynamically stable Nb 2 Ni phase is discovered within Nb-Ni binary system, refreshing the current situation that there are only three stable intermediate phases of Nb 7 Ni 6 , NbNi 3 and NbNi 8. The new stable phase is generated from the peritectoid transition: (Nb) + Nb 7 Ni 6 → Nb 2 Ni, and the transformation temperature is 1533 K. This refreshes the current equilibrium Nb-Ni binary phase diagram. It is confirmed by transmission electron microscopy and the annealing experiments, which is determined to be the FCC structure (Pearson: cF 96, space grope: Fd -3 m O 2, a = 11.888 Å). Furthermore, the equilibrium properties of Nb 2 Ni phase are produced by density functional theory, including the formation energy, cohesive energy, bulk modulus and lattice constant. [Display omitted] [ABSTRACT FROM AUTHOR]

Intermetallic compounds have the characteristics of long-range ordered structure and combination of metallic and covalent bonds, showing intrinsic brittleness and outstanding performance stability. The synthesis mechanism, pore structure characterization and material properties of powder metallurgy porous intermetallics are reviewed in this paper. Compared with traditional porous materials, porous intermetallics have good thermal impact resistance, machinability, thermal and electrical conductivity similar to metals, as well as good chemical corrosion resistance, rigidity and high-temperature property similar to ceramics. The mechanisms of preparation and pore formation of porous intermetallics mainly include four aspects: (1) the physical process based on the interstitial space between the initial particles and its evolution in the subsequent procedures; (2) the chemical combustion process based on the violent reaction between the initial powder components; (3) the reaction kinetics process based on the difference between the diffusion rates of elements; (4) the phase transition process based on the difference between the phase densities. The characterization parameters to the pore structure description for porous intermetallics include mainly overall porosity, open porosity, permeability, maximum pore size, pore size distribution and tortuosity factor. In terms of microstructure characterization of porous intermetallics, three-dimensional pore morphology scanning technology has the potential to reveal the internal characteristics of pore structures. The research on material properties of porous intermetallics mainly focuses on electrochemical catalytic activity, generalized oxidation resistivity at high temperature, resistance against chemical corrosion and mechanical properties, which have obvious advantages over traditional porous materials. In the field of the development of porous intermetallics, it is expected to expand their applications by further reducing the pore size to the nanoscale level to improve the filtration accuracy or increase the specific surface area, as well as introducing the high entropy design on the composition to improve the brittleness and enhance their material performance. [ABSTRACT FROM AUTHOR]

Currently, in the era of big data and 5G communication technology, electromigration has become a serious reliability issue for the miniaturized solder joints used in microelectronic devices. Since the effective charge number (Z *) is considered as the driving force for electromigration, the lack of accurate experimental values for Z * poses severe challenges for the simulation-aided design of electronic materials. In this work, a data-driven framework is developed to predict the Z * values of Cu and Sn species at the anode based LIQUID, Cu 6 Sn 5 intermetallic compound (IMC) and FCC phases for the binary Cu-Sn system undergoing electromigration at 523.15 K. The growth rate constants (k em) of the anode IMC at several magnitudes of applied low current density (j = 1 × 106 to 10 × 106 A/m2) are extracted from simulations based on a 1D multi-phase field model. A neural network employing Z * and j as input features, whereas utilizing these computed k em data as the expected output is trained. The results of the neural network analysis are optimized with experimental growth rate constants to estimate the effective charge numbers. For a negligible increase in temperature at low j values, effective charge numbers of all phases are found to increase with current density and the increase is much more pronounced for the IMC phase. The predicted values of effective charge numbers Z * are then utilized in a 2D simulation to observe the anode IMC grain growth and electrical resistance changes in the multi-phase system. As the work consists of the aspects of experiments, theory, computation, and machine learning, it can be called the four paradigms approach for the study of electromigration in Pb-free solder. Such a combination of multiple paradigms of materials design can be problem-solving for any future research scenario that is marked by uncertainties regarding the determination of material properties. [ABSTRACT FROM AUTHOR]

A data-driven approach combining together the experimental laser soldering, finite element analysis and machine learning, has been utilized to predict the morphology of interfacial intermetallic compound (IMC) in Sn- x Ag- y Cu/Cu (SAC/Cu) system. Six types of SAC solders with varying weight proportion of Ag and Cu, have been processed with fiber laser at different magnitudes of power (30−50 W) and scan speed (10−240 mm/min), and the resultant IMC morphologies characterized through scanning electron microscope are categorized as prismatic and scalloped ones. For the different alloy composition and laser parameters, finite element method (FEM) is employed to compute the transient distribution of temperature at the interface of solder and substrates. The FEM-generated datasets are supplied to a neural network that predicts the IMC morphology through the quantified values of temperature dependent Jackson parameter (α J). The numerical value of α J predicted from neural network is validated with experimental IMC morphologies. The critical scan speed for the morphology transition between prismatic and scalloped IMC is estimated for each solder composition at a given power. Sn-0.7Cu having the largest critical scan speed at 30 W and Sn-3.5Ag alloy having the largest critical scan speed at input power values of 40 W and 50 W, thus possessing the greatest likelihood of forming prismatic interfacial IMC during laser soldering, can be inferred as most suitable SAC solders in applications exposed to shear loads. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of YCo 5 compound have been studied by neutron diffraction, in the pressure range 0 ≤ p ≤ 7.2 GPa. The cobalt moments decrease with pressure, parallelly with anisotropic changes of lattice parameters. The experimental data are analyzed together with results from the combined Density Functional and Dynamical Mean-Field Theory. A rather good agreement between the experimentally determined and calculated values of cobalt moments is shown. Our scenario for the behavior of YCo 5 under pressure, is the combined action of the Lifshitz transition with a strong local electron-electron interaction. [ABSTRACT FROM AUTHOR]

The influence of the microstructure on mechanical properties of AlSi10Mg fabricated by casting and selective laser melting (SLM) were investigated and contrasted in this work, with an emphasis on understanding the forming mechanism. The microstructure, phase structure and mechanical properties were characterized by scanning electron microscopy/field-emission Transmission Electron Microscopy (SEM/TEM), X-Ray Diffraction (XRD), tensile and fatigue tests. The results indicated that the SLM AlSi10Mg exhibited a supersaturated Si network structure precipitated along α-Al cell. Brittle β-Al5FeSi and π-Al8FeMg3Si6 phases were found in the as-cast and SLM AlSi10Mg respectively due to different thermal histories during processing. The SLM AlSi10Mg showed higher tensile strength but lower elongation than the casting, as the result of grain refinement and tortuous crack path. The fatigue results revealed that unmelted powder, oxide inclusion and pores can considerably degrade the fatigue properties for the SLM AlSi10Mg. The SLM process offered a new method for material processing that would avoid harmful Fe-bearing intermetallic compounds and refine the microstructures for enhancing strength. [ABSTRACT FROM AUTHOR]

Exfoliation on as-extruded Mg-1Li-1Ca magnesium alloy was investigated after an immersion in 3.5 wt% NaCl aqueous solution for 90, 120 and 150 days through optical microscope, digital camera, scanning electron microscope, electrochemical workstation, scanning Kalvin probe, X-ray diffraction and Fourier transform infrared spectroscope. The results demonstrated that exfoliation corrosion occurred on extruded Mg-1Li-1Ca alloy due to elongated microstructure parallel to surface, and delamination of lamellar structure resulted from galvanic effect and wedge effect. Skin layer with fine grains exhibited better corrosion resistance, whereas the interior with coarse grains and the intermetallic compound, Mg 2 Ca particles existing in a fibrous structure, dispersed along grain boundaries and extrusion direction in a line. Furthermore, galvanic effect between Mg 2 Ca particles and their neighboring α-Mg matrix facilitated dissolution of Mg 2 Ca particles and α-Mg matrix; wedge effect was caused by formation of corrosion products. Exfoliation corrosion of extruded Mg-Li-Ca alloys might be a synergic effect of pitting corrosion, filiform corrosion, intergranular corrosion and stress corrosion. Finally, exfoliation corrosion mechanism was proposed. [ABSTRACT FROM AUTHOR]

The prospect of joining dissimilar materials via solid-state processes presents an opportunity to obtain multi-material structures having a synergy of desirable properties of the joined materials. However, the issue of the formation of intermetallic compounds at the weld interface of dissimilar materials arises with that, depending upon the temperature and pressure conditions as per phase diagram. As the thickness of the intermetallic compounds may determine the mechanical properties of the joint, understanding the driving mechanisms and evolution of these intermetallic compounds in solid-state joining processes, such as refill friction stir spot welding (refill FSSW), is crucial. In this contribution, we account for the effect of different driving forces in a multiphase-field approach and investigate the evolution of the intermetallic compounds driven by chemical and mechanical forces. A finite-element simulation of the refill FSSW is pursued to obtain the peak temperature and strain at different locations of the weld interface. The microstructure simulations obtained via the multiphase-field model give insight into the morphology and kinetics evolution of the intermetallic compounds for both, the absence of strain (purely chemically-driven model) as well as presence of strain (chemo-mechanically-driven model). The consideration of strain proves to result in thicker intermetallic compound layer. Furthermore, the impact of interface energy and initial grain configuration is found to be significant on the overall intermetallic compounds evolution. [ABSTRACT FROM AUTHOR]

Point defects play an important role in determining the structural stability and mechanical behavior of intermetallic compounds. To help quantitatively understand the point defect properties in these compounds, we developed PyDII, a Python program that performs thermodynamic calculations of equilibrium intrinsic point defect concentrations and extrinsic solute site preferences in intermetallics. The algorithm implemented in PyDII is built upon a dilute-solution thermodynamic formalism with a set of defect excitation energies calculated from first-principles density-functional theory methods. The analysis module in PyDII enables automated calculations of equilibrium intrinsic antisite and vacancy concentrations as a function of composition and temperature (over ranges where the dilute solution formalism is accurate) and the point defect concentration changes arising from addition of an extrinsic substitutional solute species. To demonstrate the applications of PyDII, we provide examples for intrinsic point defect concentrations in NiAl and Al 3 V and site preferences for Ti, Mo and Fe solutes in NiAl. Program summary Program title: PyDII Catalogue identifier: AEWI_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEWI_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: MIT License No. of lines in distributed program, including test data, etc.: 6123 No. of bytes in distributed program, including test data, etc.: 40988 Distribution format: tar.gz Programming language: Python. Computer: Any computer with a Python interpreter. Operating system: Any which enable Python. RAM: Problem dependent Classification: 7.1. External routines: NumPy [1], Sympy [2], and Pymatgen [3]. Nature of problem: Equilibrium intrinsic point defect concentrations and solute site preferences in intermetallic compounds. Solution method: Intrinsic point defect properties and solute site preference as a function of composition and temperature are computed within the grand-canonical, dilute-solution thermodynamic formalism developed by Woodward et al., Phys. Rev. B 63 (2001) 094103. Restrictions: The current version of PyDII supports generating inputs and parsing outputs for density functional calculations implemented in VASP. Defect energetics obtained from other computational methods or software can also be used to compute the defect properties by preparing the input in a format consistent with that of the JSON files provided in the example folder. Additional comments: This article describes version 1.0.0. Running time: Problem dependent References: [1] Numpy Developers, http://numpy.org/ . [2] Sympy Development Team, http://sympy.org/ . [3] S.P. Ong, W.D. Richards, A. Jain, G. Hautier, M. Kocher, S. Cholia, D. Gunter, V.L. Chevrier, K.A. Persson, G. Ceder, Python Materials Genomics (pymatgen): A Robust, Open-Source Python Library for Materials Analysis, Computational Materials Science 68 (2013) 314–319. [ABSTRACT FROM AUTHOR]

Solder size effect on early stage interfacial intermetallic compound (IMC) evolution in wetting reaction between Sn–3.0Ag–0.5Cu solder balls and electroless nickel electroless palladium immersion gold (ENEPIG) pads at 250 °C was investigated. The interfacial IMCs transformed from initial needle- and rod-type (Cu,Ni) 6 Sn 5 to dodecahedron-type (Cu,Ni) 6 Sn 5 and then to needle-type (Ni,Cu) 3 Sn 4 at the early interfacial reaction stage. Moreover, these IMC transformations occurred earlier in the smaller solder joints, where the decreasing rate of Cu concentration was faster due to the Cu consumption by the formation of interfacial (Cu,Ni) 6 Sn 5 . On thermodynamics, the decrease of Cu concentration in liquid solder changed the phase equilibrium at the interface and thus resulted in the evolution of interfacial IMCs; on kinetics, larger solder joints had sufficient Cu flux toward the interface to feed the (Cu,Ni) 6 Sn 5 growth in contrast to smaller solder joints, thus resulted in the delayed IMC transformation and the formation of larger dodecahedron-type (Cu,Ni) 6 Sn 5 grains. In smaller solders, no spalling but the consumption of (Cu,Ni) 6 Sn 5 grains by the formation of (Ni,Cu) 3 Sn 4 grains occurred where smaller discrete (Cu,Ni) 6 Sn 5 grains formed at the interface. [ABSTRACT FROM AUTHOR]

The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of lamellar-anomalous-divorced eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diffusion control. The calculated coupled zone demonstrates that (Co2Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi2) covers a composition range from 40.8% to 43.8% Si. [ABSTRACT FROM AUTHOR]