Intermetallics Research Papers - Academia.edu (original) (raw)

The compounds RPt 4 B, with (R ¼ La, Ce, Pr, Nd), were synthesized and their crystal structure was studied either by single crystal X-ray diffraction and/or by conventional and synchrotron X-ray powder diffraction. All four compounds of this family are isostructural and belong to the CeCo 4 B structure type. AC-susceptibility and magnetization studies show that: there is no magnetic ordering of the La compound down to 1.7 K; the Ce compound presents an antiferromagnetic-type-transition at 2.4 K; and both Pr and Nd compounds present a ferromagnetic-type transition at 4.2 and 4.9 K, respectively. Electrical resistivity studies show metallic behaviour for all compounds, the temperature dependence for the La compound being described by the Bloch Gruneisen relation. Thermopower studies as a function of temperature show that the thermopower is positive and small for these compounds, which is consistent with hole dominated metallic behaviour.

- by
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- Materials Engineering, Intermetallics, Crystal structure, Magnetic Properties

The exoskeleton of the lobster Homarus americanus is a multiphase biological composite material which consists of an organic matrix (crystalline α-chitin fibers and various types of non-crystalline proteins) and minerals (mainly calcite). In this study we discuss experimental data about the mesoscopic structure and the crystallographic texture (orientation distribution) of the α-chitin–protein fiber network in this material. The synchrotron measurements reveal very strong crystallographic textures of the α-chitin. According to these data, a large fraction of the α-chitin lattice cells is arranged with their longest axis parallel to the normal of the surface of the exoskeleton. Additionally, a smaller fraction of the α-chitin cells is oriented with their longest axis perpendicular to the cuticle surface. These structural investigations reveal the pronounced role of crystallographic orientation distributions in mineralized biological composite materials which may be of relevance for an improved understanding of biological and bio-inspired nano-composites.

- by Dierk Raabe
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- Materials Engineering, Mechanical Engineering, Materials Science, Crystallography

A polymorph of In 2 La was discovered by observing a change in the quadrupole interaction at nuclei of 111 In/Cd probe atoms at high temperature using the technique of perturbed angular correlation of gamma rays. Point-symmetry information from the measured electric field gradient and chemical considerations suggests that the high-temperature polymorph has the hexagonal AlB 2 structure. The transformation between the low-temperature phase, which has the CeCu 2 structure, and the high-temperature phase takes place with hysteresis over a temperature range from 200 to 450 • C.

- by Gary S. Collins
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- Materials Engineering, Condensed Matter Physics, Intermetallics

In order to establish site preference in the G-phases with Ti/Al substitution, the extensive range of the ternary solid solution for the G-phase in the Ti-CoAl system has been investigated by X-ray powder/single crystal and neutron powder diffraction. A filled variant of the Th 6 Mn 23 type (space group Fm 3m) was confirmed for the Al-rich single-phase region, whereas a novel structure variant with space group F 43m was established for the Ti-rich side of the G-phase region. Precise atom site occupation has been established for both structure types throughout the full extension of the G-phase homogeneity region.

- by Peter Rogl
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- Materials Engineering, Powder Diffraction, Intermetallics, Crystal chemistry

Fatigue damage is closely related to plastic deformation and heat dissipation, which affect the temperature of the materials. In the current research, a state-of-the-art infrared-thermography camera has been used as a nondestructive evaluation (NDE) method to investigate the temperature evolutions in both crystalline and amorphous materials during fatigue experiments. Fatigue-damage processes, such as the Lüders band growth in reactor-pressure-vessel (RPV) steels and shear-band evolution in bulk metallic glasses (BMGs), have been observed in situ and analyzed by thermography. Theoretical models combining fracture mechanics and thermodynamics have been formulated to quantify the temperature-evolution processes during fatigue. Specifically, the plastic work in RPV steel during low-cycle fatigue has been calculated and the fatigue life has been predicted from the observed temperature. The prediction matches the experimental data quite well. q

- by Peter Liaw
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- Materials Engineering, Thermodynamics, Intermetallics, Nondestructive Evaluation

The microstructural evolution of a b.c.c.-based, spinodally formed alloy Fe35Ni15Mn25Al25 has been studied as a function of annealing time at 550 °C using atom probe tomography and transmission electron microscopy, including energy-filtered imaging. The sizes, crystal structures, orientation relationships and compositions of the phases present were determined as a function of annealing time. The hardness showed complicated behavior as a function of annealing time, consisting of initial hardening, followed by softening and finally, by a rapid hardening behavior. The hardness is controlled both by the coarsening of the spinodally formed phases, and the precipitation and growth of β-Mn structured particles.

- by Ross Marceau and +1
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- Materials Engineering, Transmission Electron Microscopy, Intermetallics, Crystal structure

Diffusion couple experiments are conducted to study phase evolutions in the Co-rich part of the Co-Ni-Ta phase diagram. This helps to examine the available phase diagram and propose a correction on the stability of the Co 2 Ta phase based on the compositional measurements and X-ray analysis. The growth rate of this phase decreases with an increase in Ni content. The same is reflected on the estimated integrated interdiffusion coefficients of the components in this phase. The possible reasons for this change are discussed based on the discussions of defects, crystal structure and the driving forces for diffusion. Diffusion rate of Co in the Co 2 Ta phase at the Co-rich composition is higher because of more number of Co-Co bonds present compared to that of Ta-Ta bonds and the presence of Co antisites for the deviation from the stoichiometry. The decrease in the diffusion coefficients because of Ni addition indicates that Ni preferably replaces Co antisites to decrease the diffusion rate.

- by Soumitra Roy and +3
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- Materials Engineering, Condensed Matter Physics, Intermetallics, Crystal structure

In Part I, various models for the prediction of the occurrence and stability of Laves phases have been discussed. In the present Part II paper, an overview is given on the various types of manifestation of Laves phases in intermetallic alloy systems with emphasis on transition metal systems. Temperature-and composition-dependent as well as stress-induced phase transformations between the cubic C15 and the hexagonal C14 and C36 structural polytypes of Laves phases were observed in various binary and ternary systems. The phase fields of the different polytypes are generally separated by small two-phase fields. Some general rules for the occurrence of the different Laves phase polytypes are derived from a study of the results of experimental phase diagram investigations of various binary and ternary systems. The solubilities and site occupancies of ternary additions in the different Laves phase polytypes and the mutual miscibility of different binary Laves phases are discussed. The need for careful experimental investigations of phase equilibria is demonstrated. Existing models discussed in the preceding Part I paper are shown to fail to predict the structure and stability of the presented Laves phases in many cases. q

- by G. Sauthoff
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- Materials Engineering, Intermetallics, Transition-Metal Oxides, Phase Field

The Nd2Fe14B cylindrical magnets were treated with water solutions of alkali, acid, and salt. Mössbauer
spectroscopy was applied to study the composition and properties of the surface material of the treated
magnets. It is shown that the main phase of the permanent Nd2Fe14B magnet partly decomposes. The released
-Nd at the grain boundaries interacts with water and forms neodymium hydroxide matrix, and the released Fe
diffuses into it. The presence of Fe-Nd(OH)3 is refl ected in the paramagnet doublet in the Mössbauer spectra
of treated neodymium magnets.

- by POPESCU ANA MARIA
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- Intermetallics, Rare Earth, Rare Earth Magnets

General properties of aluminium alloys of the rare earth metals are briefly summarised. Their phase equilibria and the crystal structures of the different intermediate phases are presented and discussed. The results obtained in the experimental investigation of the Y-Al and Sm-Al systems are reported. The formation enthalpies of YA12 and SmAlz have been re-measured, resulting in-50.5kJ/(mol at) and-55.0kJ/(mol at) at room temperature, in a good agreement with literature data. Phase equilibria investigation in the Sm-Al system has been carried out and the results obtained via thermal analysis, micrographic examination, microprobe and X-ray diffraction analyses described and discussed in the framework of the general behaviour of the rare earth alloys. The experimental Sm-Al phase diagram, collated with previous literature data, is compared with the results of a thermodynamic optimisation. The following inter-metallic compounds exist: Sm2Al (peritectic decomposition, at 860°C) SmAl (per.dec.960"Q SmAl2 (melting point 148O"Q SmAls (peritectoidal decomposition at 113o"C), SmsAlr , (melting point-1380°C). The following eutectic equilibria have also been determined or confirmed: 20 at% Al and 760°C 75 at% Al and 134O"C, 97.0 at%Al and 635°C. A eutectoidal equilibrium occurs at 10 at% Al and 700°C.

- by Daniele Macciò
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- Materials Engineering, Materials Science, Thermodynamics, Intermetallics

The microstructure and oxidation behavior of sintered Nb-Mo-Si-B alloys were investigated for the phase assemblies T 1 (in the Mo-Si-B system. In the Nb-Si-B system, T 2 (Nb 5 (Si,B) 3 ) and D8 8 (Nb 5 Si 3 B x ) were investigated, while in the quaternary Nb-Mo-Si-B system, T 1 -T 2 -D8 8 was investigated. Alloys were oxidized at 1000 8C in flowing air. For Mo-Si-B compositions, the alloys showed excellent oxidation stability and initial mass loss of the alloy varied according to its Mo content. Minor quantities of MoO 2 were observed in the Mo-Si-B scales. The oxidation rates of Nb-Si-B and Nb-Mo-Si-B alloys were much larger than that of Mo-Si-B alloys. Their overall mass gains were significantly dependent on the initial heating atmosphere. In the Nb-Si-B system, T 2 and D8 8 alloys were more resistant to oxidation when heated to the test temperature in high purity argon. The quaternary Nb-Mo-Si-B alloy containing less D8 8 phase showed lower mass gains than that containing more D8 8 phase. Scales of the order of 10-50 mm thick were observed on Mo-Si-B alloys while much thicker scales, of the order of 200-600 mm, were observed on Nb-Si-B and Nb-Mo-Si-B alloys. Initial heating in argon resulted in denser scales and reduced the oxidation rate of Nb-Mo-Si-B alloys. Published by Elsevier Ltd.

- by M. Akinc
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- Materials Engineering, Intermetallics, Microstructures, Mass Loss

This research studied the electromigration effects on Sn/Ni/Sn sandwich-type couple interfacial reactions with various electric current densities at different temperatures. The Sn/Ni cathode side is always formed with a uniform Ni 3 Sn 4 layer. At the opposite Ni/Sn anode interface either Ni 3 Sn 4 or NiSn 4 could form, which depends on the reaction temperatures and current densities. The results reveal that with a current density of 1000 A/cm 2 at 180 C, the Ni 3 Sn 4 phase remains layer-structured. As the applied current exceeds 2000 A/cm 2 , Ni atoms are driven by electromigration force to migrate into the Sn matrix to form the irregular bulk Ni 3 Sn 4 and NiSn 4 . With a higher current density of 5000 A/cm 2 , large amounts of the Ni 3 Sn 4 phase are distributed into the Sn matrix and even the Ni substrate is seriously consumed. At lower temperatures, below 150 C and with 5000 A/cm 2 current, the plate-like metastable NiSn 4 phase is found in the Sn matrix at the anode side. In this electromigration study on the Sn/Ni interfacial reactions, both the reaction temperatures and the applied current densities greatly affect the reaction phase species and their morphologies.

- by Sinn-wen Chen
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- Materials Engineering, Intermetallics, Electromigration, Current Density

The cluster variation method (CVM) has been used as a tool for modelling the thermodynamics of the b.c.c. Co–Cr–Al system within the irregular tetrahedron approximation. The interaction parameters (nearest and next-nearest neighbour pairs, as well as tetrahedron interactions) for the three binary subsystems have been derived following the so-called phenomenological approach, i.e. the interaction parameters have been fitted to experimental phase diagram and/or thermochemical data. As a result, the three binary phase diagrams of the system and four isothermal sections of the ternary phase diagram have been obtained. The results show that the CVM is thermodynamically self-consistent.

- by Cláudio G Schön
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- Thermodynamics, Intermetallics, Phase Diagrams

An XPS investigation was carried out of the surface films, formed by exposure to ultrapure water, on mechanically ground Mg and the two Mg-Al intermetallic compounds: Al 3 Mg 2 and Mg 17 Al 12 . The mechanically ground Mg surface had a film of MgO at the Mg metal surface covered by a Mg(OH) 2 layer, formed by the reaction of the MgO with water vapour in the air. Upon immersion in ultrapure water, this film converted to a duplex film with an inner MgO layer next to the Mg metal and an external porous hydroxide layer. For both intermetallics, the XPS data is consistent with (i) preferential dissolution of Mg and (ii) a 10 nm thick film on the surface after immersion in ultrapure water; the film composition on Al 3 Mg 2 was AlMg 1:4 O 0:2 ðOHÞ 5:4 whilst on Mg 17 Al 12 the composition was AlMg 2:5 ðOHÞ 8 .

- by H. Ardelean and +2
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- Materials Engineering, Mechanical Engineering, Civil Engineering, Corrosion Science

Topologically close-packed (TCP) phases with complex structures are often observed in high entropy alloys (HEAs). Currently, these TCP phases are garnering significant interest from both theoretical and experimental perspectives due to the ductility deterioration of the high strength HEAs. Alternatively, there are instances when TCP phases can actually benefit the mechanical performances of alloys, such as the wear resistance. Therefore, the stability of TCP phases should be taken into consideration in the alloy design. In this paper, the relationship between the TCP phase stability and the physicochemical/thermodynamic properties of alloying components in HEAs was systematically studied. The stability of TCP phases was found to correlate well with the electro-negativity difference (DX) for most of the reported HEAs. The stability of TCP phases is well delineated by the electro-negativity difference (DX): i.e., TCP phases are stable at DX > 0.133 except for some HEAs that contain a significant amount of aluminum.

- by Yongdong Chen
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- Materials Engineering, Intermetallics

Dependence of phase transformation temperatures of TiPd-and TiPt-based shape memory alloys on valence electron ratio (VER), number (e v /a), and average atomic number of the alloys (Z) are investigated. The alloys have medium numbers of valence electrons (6.6 B e v /a B 7.3) that are near 7 and a wide range of the average atomic number (Z = 25-54). The forward and reverse phase transformation temperatures, M s and (A s), increase with average atomic number of the alloys, respectively. Clear correlations between transformation temperatures and VER are found. M s and (A s) both decrease from around 1184°C (1175°C) to as low as 20°C (32°C), respectively, with increasing VER from 0.134 to 0.270. Temperature hysteresis of the thermoelastic transformation in these alloys tends to decrease with increasing VER. Dependence of transformation temperatures and temperature hysteresis of these shape memory alloys on VER is discussed based on the variations of elastic moduli and atomic bonding due...

- by mz Mz
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- Materials Science, Physical Metallurgy (Physics), Metallurgy, Intermetallics

Gas atomized Tie48Ale2Cre2Nb powders have been used as precursor material in order to evaluate additive manufacturing for the production of near-net-shape g-TiAl specimens to be employed in the field of aero-engines. In particular electron beam melting (EBM) is used to realize a selective densification of metal powder by melting it in a layerwise manner following a CAD design. The microstructure, the residual porosity and the chemical composition of the samples have been investigated both immediately after EBM and after heat treatments. High homogeneity of the samples, very low pickup of impurities (oxygen and nitrogen) with respect to the starting powders have been observed and due to an extremely low level of internal defects, intrinsic to EBM process, the tensile properties of the EBM g-TiAl appear very consistent with a small scatter.

- by Paolo Fino and +2
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- Materials Engineering, Heat Treatment, Intermetallics, Nitrogen

Recent binary thermodynamic descriptions are used as a starting point for the modelling of the ternary Nb–Ni–Si phase diagram. First-principles electronic structure calculations, within the framework of the Density Functional Theory (DFT), are performed for the determination of formation energies of known ternary compounds. The results are introduced into a CALPHAD-type thermodynamic model using the Compound Energy Formalism (CEF). The model parameters are then optimised in order to match the experimental 1073 K isothermal section of the ternary phase diagram.

- by Cláudio G Schön and +1
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- Thermodynamics, Intermetallics, Phase Diagrams, Multicomponent Alloys

The thermodynamic properties and phase diagrams of the Mo±Si and Al±Mo±Si systems are assessed, and a complete thermodynamic description is obtained. The calculation results show good agreement with the experimental data. The high temperature phase equilibria involving the C40 and C11 b MoSi 2 structures in the Mo±Si binary and Al±Mo±Si ternary systems have been clar-i®ed. #

- by Guosheng Shao
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- Materials Engineering, Intermetallics

A re-assessment of the thermodynamic parameters of the binary Cr–Ti system and a first assessment of the ternary Al–Cr–Ti system were performed. The new Cr–Ti description contains all three modifications of the Laves phases (α-TiCr2, β-TiCr2, γ-TiCr2) and the calculated binary phase diagram is in very good agreement with the experimental data. For a first assessment of the Al–Cr–Ti system,

- by Olga Fabrichnaya and +1
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- Materials Engineering, Thermodynamics, Intermetallics, Experimental Data

The present article presents the effect of Sc addition on the secondary dendritic arm spacing, eutectic Si modification , intermetallic phase modification, aging behavior and subsequently the mechanical behavior in A356-5TiB 2 in-situ composite. The A356-5TiB 2 in-situ composite showed a 40% reduction in SDAS compared with A356 alloy, whereas addition of 0.4 wt% Sc and 5 wt% TiB 2 in A356 alloy resulted in a 65% reduction in SDAS. The eutectic Si in A356-5TiB 2 composite had a plate like morphology similar to A356 alloy but showed a reduction in length, whereas the addition of Sc resulted in a fibrous and particulate morphology of eutectic Si. The needle like β-Al 5 FeSi phase in A356-5TiB 2 composite changed to Al 5 Fe(Si,Sc) phase having smaller size and irregular morphology with the addition of Sc. The intermetallic phase formation and phase modification was confirmed and characterized using X-ray diffraction, Transmission electron microscopy-Energy dispersive spectroscopy and Scanning electron microscopy. Addition of Sc to A356-5TiB 2 in-situ composite resulted in improved mechanical properties. Further, T6 heat treatment revealed a significant improvement in mechanical properties for A356-5TiB 2 in-situ composite with and without Sc addition.

To manufacture propulsion systems of satellites it is necessary to develop and qualify special union procedures, such as high temperature brazing and laser or solid state diffusion welds. In particular this work describes the recent experience to qualify a brazing process for aerospace use, specifically for the fabrication of a 5N thruster propulsion system, working with hydrazine as monopropellant, for the multimission platform (PMM) of the Brazilian Space Agency. The brazed components were the capillary tube injector and the capillary tube of the pressure line test ground coupling injector, fabricated in Inconel 600 and austenitic stainless steel AISI 304. The brazing process was realized in high vacuum, lower than 4.10 -5 mbar, at the temperature of 1100°C. Two Ni-based brazing alloys, BNi-1a and BNi-2, as paste and amorphous metallic foil were tested. Joint gap and brazing thermal cycle were adjusted to avoid the presence of intermetallic phases, which occurrence in a brazed Inconel600/BNi-2 union increased the hardness until 1142HV. Wetability and metallographic tests indicate the BNi-1a metallic foil, as the most adequate for this application. Leakage rates lower than 4.10 -7 mbar l/s assured the tightness of the brazed unions.

- by AUGUSTO BUSCHINELLI
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- Mechanical Engineering, Intermetallics, Propulsion Systems, Stainless Steel

Two refractory high-entropy alloys with near-equiatomic concentrations, WeNbeMoeTa and WeNbeMoeTaeV, were produced by vacuum arc melting. Despite containing many constituents both alloys have a single-phase body-centered cubic (BCC) structure. The lattice parameters a ¼ 3.2134(3) A for the quaternary alloy and a ¼ 3.1832(2) A for the quinternary alloy were determined with high-energy X-ray diffraction using a scattering vector length range from 0.7 to 20 A À1 . The alloy density and Vickers microhardness were r ¼ 13.75 g/cm 3 and H v ¼ 4455 MPa for the WeNbeMoeTa alloy and r ¼ 12.36 g/cm 3 and H v ¼ 5250 MPa for the WeNbeMoeTaeV alloy. The exceptional microhardness in these alloys is greater than any individual constituent, suggesting the operation of a solid-solution-like strengthening mechanism.

- by Peter Liaw
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- Materials Engineering, Intermetallics
- by Vadim Silberschmidt
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- Materials Engineering, Intermetallics

Ultrafine grained steels with grain sizes below about 1 m offer the prospect of high strength and high toughness with traditional steel compositions. These materials are currently the subject of extensive research efforts worldwide. Ultrafine grained steels can be produced either by advanced thermomechanical processes or by severe plastic deformation strategies. Both approaches are suited to produce submicron grain structures with attractive mechanical properties. This overview describes the various techniques to fabricate ultrafine grained bcc steels, the corresponding microstructures, and the resulting spectrum of mechanical properties.

- by Dierk Raabe
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- Materials Engineering, Mechanical Engineering, Materials Science, Crystallography

High-entropy alloys (HEAs) have recently become a vibrant field of study in the metallic materials area. In the early years, the design of HEAs was more of an exploratory nature. The selection of compositions was somewhat arbitrary, and there was typically no specific goal to be achieved in the design. Very recently, however, the development of HEAs has gradually entered a different stage. Unlike the early alloys, HEAs developed nowadays are usually designed to meet clear goals, and have carefully chosen components, deliberately introduced multiple phases, and tailored microstructures. These alloys are referred to as advanced HEAs. In this paper, the progress in advanced HEAs is briefly reviewed. The design strategies for these materials are examined and are classified into three categories. Representative works in each category are presented. Finally, important issues and future directions in the development of advanced HEAs are pointed out and discussed.

Aluminum (Al) and copper (Cu) have been widely used in many industrial fields thanks to their good plasticity, high thermal conductivity and excellent electrical conductivity. An effective joining of dissimilar Al and Cu materials can make full use of the special characteristics of these two metals. Friction stir spot welding (FSSW), as an efficient solid-state welding method suitable for joining of dissimilar metal materials, has great prospects in future industrial applications. In this paper, the FSSW studies on Al-Cu dissimilar materials are reviewed. The research progress and current status of Al-Cu FSSW are reviewed with respect to tool features, macroscopic characteristics of welded joints, microstructures, defects in welds and mechanical properties of joints. In addition, some suggestions on further study are put forward in order to promote the development and progress of Al-Cu FSSW studies in several respects: material flow, thermal history, addition of intermediate layer, auxiliary methods and functionalization of Al-Cu FSSW joint.

- by Chaoqun Zhang
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- Welding Engineering, Intermetallics, Welding and Joining, Aluminum

This study provides an in-depth investigation into low-cost and no-cost substrate release mechanisms that allow gas metal arc weld 3-D printed ER4043 aluminum and ER70S-6 steel parts to be removed from a reusable print substrate with minimal energy. Aluminum oxide, boron nitride, and titanium nitride coatings were evaluated as possible substrate release agents for aluminum printing. Additionally, the in situ formation of substrate release agents such as intermetallics and oxides were tested for both aluminum and steel printing. Testing was performed with a modified Charpy impact tester to remove 3-D printed metal parts from an 1100 aluminum or A36 low carbon steel print substrate to assess the impact energy required for removal. Specimen porosity was measured prior to sectioning and microstructural analysis, hardness traverses were measured across the specimens, and the elastic and shear moduli of the parts were analyzed via ultrasonic methods. All of the employed substrate release mechanisms minimized weld penetration and, in some instances, formed a brittle phase with the print substrate that allowed the specimens to be removed with minimal impact energy. These results thus provide methods with the removal of metal 3-D printed parts from print substrates with no specialized tooling or equipment conducive to distributed manufacturing.

- by Joshua Pearce
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- Recycling, Metallurgy, Intermetallics, 3D printing

E n esta memoria de Tesis Doctoral se presentan los resultados del estudio del efecto magnetocalórico y magnetovolúmico que se ha llevado a cabo en dos familias de compuestos ricos en Fe: aleaciones R 2 Fe 17 , sintetizadas en forma policristalina, y cintas amorfas de composición FeZrBCu. Estas aleaciones presentan transiciones magnéticas de segundo orden con temperaturas críticas en torno a temperatura ambiente.

- by Pablo Alvarez-Alonso and +1
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- Intermetallics, Amorphous Materials, Magnetic nanoparticles, Magnetocaloric Effect

High entropy alloys (HEA) are multicomponent (5 or more) massive solid solutions with an equiatomic or a near equiatomic composition. The original ideal of investigating multicomponent alloys in equal or near-equal proportions represents a new alloy exploration strategy. Instead of starting from a corner of a phase diagram with one prevalent base element, it has been suggested that new materials could be identified by directly producing equiatomic compositions with multiple components. The term ‘‘high entropy alloys’’ was introduced by Yeh et al., based on the hypothesis that the high configurational entropy would stabilize the solid solution phase over competing intermetallic and elemental phases. A well-studied HEA is the Cantor alloy i.e. Co20Cr20Fe20Mn20Ni20 (at.%) which develops a single phase fcc solid solution. Recently, it has been shown that a non-equiatomic composition of this alloy system also exhibits a single phase fcc solid solution irrespective of its slightly lower mixing entropy. The objective of this study is two-fold. One focus is the prediction and analysis of the phase stability of this alloy system i.e. FexMn62ÿxNi30Co6Cr2 (at.%, x = 22, 27, 32, 37, and 42), while varying the Fe and Mn contents, and maintaining the compositions of Cr, Co and Ni constant. The configurational entropy of these alloys ranges from 1.295 to 1.334 kB/atom (kB is the Boltzmann constant) which yields 80–83% of that in equiatomic composition (1.6094 kB/atom) as shown in Fig. 1. Another focus is to explore the feasibility of using the CALPHAD (CALculation of PHAse Diagrams) method for future knowledge based approaches to the design of HEAs. Compared with other approaches for designing HEAs (e.g. empirical rules, or ab initio based methods), the CALPHAD method provides an optimal balance between efficiency and accuracy. On the other hand, most multicomponent systems are not fully covered by the available CALPHAD databases. Instead, current CALPHAD simulations of multicomponent systems are based on the extrapolation from binary, ternary, and, (perhaps) quaternary systems. Hence, the accuracy of the corresponding predictions yielded by
using a CALPHAD approach needs to be critically evaluated.
The objective of this study is to experimentally and theoretically investigate the phase stability of non-equiatomic FexMn62ÿxNi30Co6Cr2 based high entropy alloys, where x ranges from 22 to 42 at.%. Another aim is to systematically and critically assess the predictive capability of the CALPHAD approach for such high entropy alloy systems. We find that the CALPHAD simulations provide a very consistent assessment of phase stability yielding good agreement with experimental observations. These include the equilibrium phase formation at high temperatures, the constituent phases after non-equilibrium solidification processes, unfavorable segregation profiles inherited from solidification together with the associated nucleation and growth of low temperature phases, and undesired martensitic transformation effects. Encouraged by these consistent theoretical and experimental results, we extend our simulations to other alloy systems with equiatomic compositions reported in the literature. Using these other equiatomic model systems we demonstrate how systematic CALPHAD simulations can improve and accelerate the design of multicomponent alloy systems.

- by M. Duancheng and +1
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- Thermodynamics, Computational Materials Science, Segregation, Electron Backscatter Diffraction (EBSD)
- by G. Sauthoff
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- Materials Engineering, Intermetallics, Intermetallic Compound

In the present contribution, recent developments of coatings for hot stamped steels are reviewed. The use of bare steel in the initial hot stamping technology is discussed, including the application of lubricant oils which are used as oxidation inhibitors on bare steel surfaces. The aluminized coatings are introduced, focusing on the microstructure evolution of aluminized coatings during the hot stamping process. An analysis of the cracking of the coating, caused by the formation of brittle Fe-Al intermetallic phases and their high temperature deformation, is presented. The development of a ductile aluminide coating formed during the diffusion treatment of an aluminized coating is discussed. This aluminide coating can endure both high temperature oxidation and severe plastic deformation. The recently developed galvanized and galvannealed coatings are also reviewed and the influence of the gas atmosphere during the heating cycle on the coating stability is emphasized. The solutions which have been proposed to avoid liquid Zninduced embrittlement are analyzed. The use of Zn-Ni alloy coating, which is characterized by a higher melting temperature, is reviewed. The behavior of sol-gel hybrid coatings on hot stamped steels is discussed. The possible use of the recently developed Al-Zn alloy coatings, dual layer Zn-Al and Zn-Al-Mg coatings is also introduced. The application of Zn-Al-Mg post-process galvanizing is also discussed. In each case, all available information related to the weldability, paintability, and corrosion resistance of the coating systems is also reported. Finally, the advantages and technical challenges associated with each type of coating are reviewed.

- by Bruno De Cooman
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- Materials Engineering, Intermetallics, Steel, Manufacturing Engineering

The phase diagram of the Ca-Si system has been investigated across almost the whole composition range (0 to 70 at% Si) using differential thermal analysis, metallographic analysis, X-ray diraction and electron microscopy. Six intermediate phases have been found: Si 3 (Cr 5 B 3 -type) and Ca 2 Si (anti-PbCl 2 -type). Ca 3 Si 4 , not previously known, is a Zintl phase representative of a new structural type: hexagonal hP42, a=854.1, c=1490.6 pm, space group P6 3 /m. Three eutectics occur in this system: at about 3.5 at% Si and 795 C, 42.5 at% Si and 1230 C, 72.0 at% Si and 1020 C. #

- by Pietro Manfrinetti
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- Materials Engineering, Electron Microscopy, Intermetallics, X ray diffraction

We have investigated the hydrogenation and dehydrogenation properties of binary RNi 5 (R: La, Pr, Nd, Sm, Gd, Tb and Dy) intermetallic compounds in the pressure range of 0.1-35 MPa and temperature range of 223-298 K. Pressure-composition isotherms demonstrated that as the atomic number of R increased in RNi 5-H systems, the single pressure plateau (LaNi 5) split into two plateaux (PrNi 5 , NdNi 5 , SmNi 5 and GdNi 5), and then into three plateaux (TbNi 5 and DyNi 5), indicating the presence of two hydrides (β 2 and γ 2 phases) and then three hydrides (β 3 , γ 3 and δ 3 phases). The β 3-γ 3 and γ 3-δ 3 phase transitions in the TbNi 5-H system corresponded, respectively, to the α 2-β 2 and β 2-γ 2 transitions in the RNi 5-H (R: Pr, Nd, Sm and Gd) systems having two plateaux.

- by N. Kuriyama
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- Materials Engineering, Condensed Matter Physics, Chemistry, Intermetallics

A large number of ab-initio calculations of energies of formation of intermetallic compounds have been performed in the last 15 years. The currently used methods are listed. The paper presents a review of the aluminium based compounds which have been studied. Comparisons of calculated and experimental enthalpies of formation are provided for aluminim-3d and-4d transition metal alloys at equiatomic composition. The modelling of the enthalpies of mixing of solid solutions based on a given lattice is described.

- by Catherine Colinet
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- Materials Engineering, Thermodynamics, Intermetallics, Ab Initio Calculation

A five-component Al x CoCrFeNi high-entropy alloy (HEA) system with finely-divided Al contents (x in molar ratio, x ¼ 0e2.0) was prepared by vacuum arc melting and casting method. The effects of Al addition on the crystal structure, microstructure and mechanical property were investigated using Xray diffraction (XRD), scanning electron microscopy (SEM), and Vickers hardness tester. The as-cast Al x CoCrFeNi alloys can possess face-centered cubic (FCC), body-centered cubic (BCC) or mixed crystal structure, depending on the aluminum content. The increase of aluminum content results in the formation of BCC structure which is a dominant factor of hardening. All the BCC phases in the as-cast alloys have a nano-scale two-phase structure formed by spinodal decomposition mechanism. The Al 0.9 CoCrFeNi alloy exhibits a finest spinodal structure consisting of alternating interconnected twophase microstructure which explains its maximum hardness of Hv 527 among the alloys. The chemical composition analysis of FCC and BCC crystal structures, their lattice constants, overall hardness demonstrate that the formation of a single FCC solid solution should have Al addition <11 at.% and the formation of a single BCC solid solution requires Al addition at least 18.4 at.% in the Al x CoCrFeNi system. Intermetallics j o u r n a l h o m e p a g e : w w w . e l s e v ie r . c o m / l o c a t e / i n t e r m e t 0966-9795/$ e see front matter Ó

- by Jien-wei Yeh
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- Materials Engineering, Intermetallics

Sn-Ag-Cu alloys have emerged as the most promising lead-free solder series among a number of alternatives. These alloys generally present a dendritic Sn-rich matrix surrounded by a eutectic mixture (b + a), where b is the Sn-rich phase and a is the Ag 3 Sn intermetallic compound. The present study aims to investigate the effects of dendritic (k 2 , k 3 ) and eutectic (k) spacings and the morphology of Ag 3 Sn particles on hardness of the Sn-3.0 wt%Ag-0.7 wt%Cu alloy (SAC307). In order to establish correlations between k 2,3 and hardness, transient directional solidification (DS) experiments were performed permitting a wide range of different microstructures to be examined. The techniques used for microstructure characterization included dissolution of the Sn-rich matrix, optical/scanning electron microscopy. A dendritic microstructure prevailed in the entire DS casting. It is shown that the hardness tends to decrease with the increase in k 2 , k 3 and k F (eutectic spacing for Ag 3 Sn having a fiber morphology). Experimental equations relating microstructural spacings to hardness are proposed.

- by Amauri Garcia
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- Microstructure, Intermetallics, Hardness, Electrical And Electronic Engineering

A detailed investigation of the phase relations in the Ti-Si-B system involving as-cast and heat-treated samples that were characterized via X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Wavelength Dispersive Spectroscopy (WDS) microprobe analysis has shown the existence of a new ternary phase of composition Ti 6 Si 2 B. Rietveld refinement of X-ray powder intensity data revealed a hexagonal crystal structure, with lattice parameters a=0.68015 nm and c=0.33377 nm and proved isotypism with the Ni 6 Si 2 B-phase (Fe 2 P-type structure, Zr 6 CoGa 2 ternary variant). The Ti 6 Si 2 B-phase forms from the liquid through the peritectic reaction: L+TiB+Ti 5 Si 3 ()Ti 6 Si 2 B. At 1200 C it forms narrow two-phase fields with Ti ss , Ti 5 Si 3 and TiB. #

- by Alfeu Ramos
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- Materials Engineering, Scanning Electron Microscopy, Titanium, Intermetallics

This paper addresses the issue of environmentally-assisted fatigue crack propagation in metallic and intermetallic alloys, which is essential to predict the durability of aerospace components. A review of the current understanding of the mechanisms accounting for the detrimental effect of air on fatigue crack growth resistance of conventional alloys is first presented. The adequacy of the two sequential processes identified, namely water vapour adsorption on crack tip surfaces and hydrogen embrittlement of cyclically deformed material within the plastic zone, to account for environmentally-assisted fatigue crack propagation in alloys based on intermetallic compounds is then examined. The last section is devoted to the analysis of environmental effects during creep-fatigue crack growth in an age-hardened aluminium alloy for supersonic aircraft. In particular the influence of environment on the intergranular cavitation damage process is analysed.

The hardness and indentation cracking at room temperature as well as the yield and creep at high temperatures in the range 800 -1400 C have been studied for various Laves phases AB 2 with the transition metals A=Zr, Nb, Ta and B=Cr, Fe, Co with partial substitution of the B elements Fe and Co by Al, which effects a transition from cubic C15 structure to hexagonal C14 structure in the case of Nb(Co,Al) 2 . These phases are brittle with a thermally activated brittle-to-ductile transition at about 2/3 of the melting temperature. Above the brittle-to-ductile transition temperature deformability is still restricted with possible deformation twinning and in addition with possible microcracking at higher strains. A close positive correlation of the yield stress, hardness and apparent activation energy of creep with the sublimation enthalpy is observed which is analogous to Gru¨neisen's first rule for the elastic bulk modulus. #

- by G. Sauthoff
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- Materials Engineering, Intermetallics, Transition-Metal Oxides, Activation Energy

Enthalpies of formation of binary Laves phases have been critically surveyed and reviewed in this paper. The enthalpy-of-formation data indicate that both geometric and electronic factors are important in stabilizing Laves phases. Analysis of enthalpy data reveals that there are metallic, covalent, and ionic bonds, or a mixed metallic-covalent-ionic bond, in Laves phases. The enthalpies of formation for binary transition-metal lanthanide Laves phases including ReCo 2 , ReNi 2 , ReFe 2 , ReRu 2 , ReRh 2 , ReOs 2 , ReIr 2 , and RePt 2 (Re-lanthanide element), as calculated by the semiempirical Miedema model, are found to be in good agreement with the available experimental data. This indicates that Miedema's theory is capable of predicting the enthalpy of formation of transition-metal lanthanide Laves-phase systems. #

- by Peter Liaw
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- Materials Engineering, Intermetallics

Ab-initio methods have been employed to investigate the electronic and elastic properties of beryllium chalcogenides (namely BeS, BeSe and BeTe). The electron momentum density, autocorrelation function and energy band gap have been computed using the linear combination of atomic orbitals method. Using the full potential linearized augmented plane-wave and projector-augmented wave methods, the energy bands and density of states (DOS) along with elastic properties are also calculated. The electronic band structure, total and partial DOS and elastic moduli obtained from the present calculations are found to be in good agreement with available earlier data. The calculated valence band width, equal valence electron density curve and bulk modulus confirm the trend of ionicity BeS>BeSe>BeTe.

- by Vinit Sharma
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- Condensed Matter Physics, Quantum Physics, Intermetallics, Ab initio calculations

First principles calculations of the structural, thermodynamic, electronic and vibrational properties of C1 b -NiTiSn half-Heusler compounds have been performed. The enthalpy of formation of C1 b -NiTiSn has been obtained. The phonon density of states has allowed to derive a value of the Debye temperature of the compound. The enthalpies of formation of point defects have been calculated using large supercells. Four sublattices have been introduced to account for the C1 b structure and for the possibility of inserting atoms in the 4d Wyckoff positions of the F4 À 3m structure. The most stable defects are I Ni and V Ni . The corresponding densities of states have been computed.

- by Catherine Colinet
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- Materials Engineering, Intermetallics

Laves phases form the largest group of intermetallic phases. Although they are well known since long, there are still unsolved problems concerning the stability of the respective crystal structures. The Laves phases crystallize with a cubic MgCu 2 -or a hexagonal MgZn 2 -or MgNi 2 -type structure which differ only by the particular stacking of the same four-layered structural units. It is still not possible to predict which of the structure types is the stable one for a Laves phase compound AB 2 . Phase transformations from a cubic low-temperature structure to a hexagonal high-temperature structure were observed as well as stress-induced transformations from the hexagonal structure to the cubic one. In addition, deviations from the stoichiometric composition were reported to result in a change of the stable polytype in various systems. In this first of two consecutive papers dealing with fundamental aspects of the stability of Laves phases, some factors which are known to affect the occurrence and structure type of Laves phases are discussed and it is shown that, at least up to now, the existing models and calculations are not well suited to give a general description of the stability of Laves phases. q

- by G. Sauthoff
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- Materials Engineering, Intermetallics, Crystal structure, Phase Stability

An attempt has been made to develop a new metallic glass (MG) that combines high hardness with wear resistance. Refractory metallic films of W 33 Ni 32 B 35 (at.%) have been deposited on stainless steel and Si substrates by dc magnetron sputtering. The alloy films are glassy, have a high crystallization temperature of 873 C and rank among the very hard metallic materials (w24 GPa). Importantly, this MG also shows excellent wear resistance, approaching that of standard tribological materials like TiN and hence it represents one of the most wear-resistant known metallic materials. Based on its unique combination of high strength and low elastic modulus, other potential applications are also discussed.

- by Shantanu Madge and +1
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- Materials Engineering, Intermetallics

For explaining asymmetry in the flow stress of Ni 3 Al alloy as a function of aluminum content, the structural energy of ordered NiAl alloy with the L1 0 structure is obtained with the electronic structure calculations based on the density functional theory. Quite a large distortion in the c-direction is found at the equilibrium, which means an L1 0 -like local structure appearing in the Al-rich region of the Ni 3 Al phase undergoes a large tetragonal strain. This tetragonal strain will give an explanation for the strengthening mechanism using the framework of Cochardt et al. The effect of the Al concentration on the structural stability of L1 0 in terms of the DOS is also discussed to explain the concentration dependence of the B2-L1 0 martensitic transition temperature. q

- by 哲夫毛利
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- Materials Engineering, Intermetallics