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Defect-free joints of NiTi/austenitic stainless steel wires have extraordinary combined properties of shape memory, superelasticity, and biocompatibility. However, problems arise from the dissimilar welding of NiTi to stainless steel, including the formation of brittle intermetallic compounds and the loss of shape memory and superelastic properties. To overcome the welding challenges of these alloys, phases formed in the weld zone must be identified. Therefore, we used CALPHAD quaternary phase analysis to predict the formation of intermetallic compounds and other probable phases in the weld zone. The calculated results were compared with existing ternary phase diagrams containing Fe, Ni, Ti, and Cr. According to these calculations and experimental observations using electron backscatter diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and micro X-ray diffraction techniques, brittle Fe2Ti is the predominant phase in the final solidified structure, even in the equilibrium state at the NiTi-weld interface. In addition, a ductile Ni3Ti phase, together with the γ-(Fe,Ni) and B2-(Fe,Ni)Ti phases, is feasible in the weld zone. Moreover, Cr appears as a solid solution with Fe and Ti (BCC_A2 and β(Cr,Ti)) at low Cr concentrations. At higher concentrations, Cr can potentially appear as a σ phase and a C14 Laves phase, which can cause a stress concentration at the NiTi-weld interface, degrading the mechanical properties of dissimilar joints. Therefore, a suitable modification process is required to improve the mechanical properties of NiTi to stainless steel joints. Thus, any adopted strategy should preclude brittle Fe2Ti and facilitate the formation of more ductile phases such as γ-(Fe,Ni). more...

Multi-principal element alloys (MPEAs) occur at or nearby the centre of the multicomponent phase space, and they have the unique potential to be tailored with a blend of several desirable properties for the development of materials of future. The lack of universal phase diagrams for MPEAs has been a major challenge in the accelerated design of products with these materials. This study aims to solve this issue by employing data-driven approaches in phase prediction. A MPEA is first represented by numerical fingerprints (composition, atomic size difference , electronegativity , enthalpy of mixing , entropy of mixing , dimensionless $$\Omega$$ Ω parameter, valence electron concentration and phase types ), and an artificial neural network (ANN) is developed upon the datasets of these numerical descriptors. A pyMPEALab GUI interface is developed on the top of this ANN model with a computational capability to associate composition features with remaining other input features. With the GUI interface, an user can predict the phase(s) of a MPEA by entering solely the information of composition. It is further explored on how the knowledge of phase(s) prediction in composition-varied $$\hbox {Al}_x$$ Al x CrCoFeMnNi and $$\hbox {CoCrNiNb}_x$$ CoCrNiNb x can help in understanding the mechanical behavior of these MPEAs. Graphic Abstract more...

Data Availability Statement: The data presented in this manuscript is available on request from the corresponding author. Copyright: © 2022 by the authors. The main problem of recycling aluminium scrap is the gradual accumulation of impurities, especially iron, which tend to form undesired intermetallic compounds that affect the integrity and the mechanical performance of the castings. In this paper, we aim to provide an overview on the topic of iron removal from aluminium melts through primary intermetallic precipitation and the progress made during the LiME Hub project to understand the process and to develop a more efficient procedure. We cover both thermodynamic analysis and experimental validation. We found that high shear melt conditioning technology enhances the typically slow nucleation and growth of the dense primary intermetallics, speeding up their sedimentation and allowing a faster removal of Fe from the melt by simple gravity sedimentation. It also promotes the formation of smaller and more compact Fe-rich intermetallics, allowing an increased volume fraction recovery and mitigating their effect of being present in the final castings. The technology is not limited to batch processing, with a 90% efficiency, but can also be applied to continuous melt treatment of aluminium scrap, with currently 60% efficiency, and could be combined with other solid–liquid separation techniques to increase the purification efficiency even more. EPSRC (UK) under grant number EP/N007638/1; European Commission under Grant No. 603577; Innovate UK under Project No.102797. more...

In this work, directional solidification method was used to investigate the growth characteristics of intermetallic compounds whose solubilities are narrow during solidification of Sn-9at.%Co peritectic alloy (L+CoSn→CoSn2). In this work, the transition of the leading phase during solidification is observed in all samples. By the application of the Interface Response Function (IRF), the calculated velocity range for the transition of the primary phase by the peritectic phase ranges from 0.501 μm/s to 398 μm/s. Moreover, the phase transition of CoSn and CoSn2 intermetallic compounds does not initiate from the initial growth interface, and the distance required for the occurrence of the phase transition is found to increase with increasing growth velocity. The measurement of the hardness and Young's modulus was accomplished by nanoindentation with the continuous stiffness measurement (CSM) technique. The elastic modulus is nearly constant while the hardness increases with increasing growth velocity. In addition, the hardness of CoSn2 phase is lower than that of CoSn phase. more...

Metallurgical systems containing substantial amounts of metallic indium have always been very challenging to investigate due to the difficulties involved with sample characterization caused by the substantial softness of indium. Such difficulties are overcome in this study, and artifact-free microstructures are successfully obtained for the first time by using cryogenic broad Ar beam ion polishing for the reactions between Cu and molten indium at 180 ℃. A two-phase layer consisting of Cu11In9 and In forms at the Cu/In interface. The growth of this layer follows parabolic kinetics, indicating that it is a diffusion-controlled process. Within the layer, Cu11In9 islands are larger near the In side than those near the Cu side, suggesting that coarsening of the Cu11In9 islands occurs. During the cooling process after the reaction, large faceted Cu11In9 islands heterogeneously precipitate over the two-phase layer. Simultaneously, nonfaceted Cu11In9 particles homogeneously precipitate within the In phase. more...

As a novel high-temperature solder with suitable eutectic temperature and excellent solderability, Au–30Ga eutectic alloy shows high application potential as a packaging material for high-power devices. In this work, the evolution of microstructure, shear strength and fracture mechanism of Au–30Ga/Ni solder joint during soldering and aging was studied. It was found that with the increase of soldering time, Ga was seriously consumed to form Ga–Ni interfacial intermetallic compounds (IMCs), resulting in the formation of Ga-poor region near the interface layer. Au7Ga3 phase would be first formed at the valley area of Ga3Ni2 IMC layer. The dominant IMCs growth mechanism eventually transformed from grain-boundary diffusion to volume diffusion after soldering for 0.49 min. The diffusion coefficients are 1.64 × 10−14 and 3.77 × 10−19 m2/s at 500 °C (soldering) and 300 °C (solid-state aging), respectively. With the coarsening of IMC layers, the fracture mechanism of joint changed from solder control mode to solder/IMC mixed control mode. When the thickness is 4.36 μm, the joint strength reaches the maximum value of 77.7 MPa. Furthermore, a reliability evaluation equation of Au–30Ga/Ni solder joint was established to optimize soldering process and solder composition. more...

Despite the large amount of literature on high entropy alloys (HEAs) in recent years, reports on the equilibrium/near-equilibrium phase and microstructure of HEAs are still very limited. Here, we investigate the phase constituents of four CoCrFeNiX (X = Y, Ti, Zr, Hf) HEAs after prolonged annealing. It is found that the alloys typically contain two major phases – a dominating intermetallic (IM) phase and a BCC phase. The major phases in general remain unchanged regardless of annealing temperature. Annealing at lower temperatures, however, typically leads to the formation of new minor phases. In particular, the formation of σ phase during annealing is observed in all the alloys. Existing phase formation theories are applied to the alloys. The theories successfully predict that the present alloys do not form simple solid solution phases only. Phase-specific stability criteria also explain the prevalence of Laves and σ phases quite well. more...

To offer a response to the increasing interest on high-temperature shape memory alloys, mainly driven by the aeronautic and aerospace industries, the design and characterization of Cu-Al-Ni shape memory alloys with high transformation temperatures, between 373 K and 473 K, are approached. The present alloy design is based on the transformation from cubic β3 austenite to the monoclinic β'3 martensite, which offers the advantage of exhibiting not only higher transformation temperatures but also a thermal hysteresis of about 12 K, much smaller than the orthorhombic γ'3 martensite historically considered for this alloy system. The influence of the alloy concentration and the thermal treatments, on the martensitic transformation temperatures is systematically analyzed and a quantitative and predictive equation is proposed. The influence of the stress on the transformation was also studied under two experimental conditions: at constant stress as a function of temperature (shape memory effect) and at constant temperature as a function of the stress (superelastic effect). A double stress-induced transformation from β3 to β'3 and α'3 with an outstanding reversible and reproducible 24% superelastic strain is also reported. The experimental results allows also determine the Clausius-Clapeyron diagrams for this series of alloys, as a fundamental tool for further design of sensing and actuating devices based on these high-temperature shape memory alloys. more...

This work investigated the interaction between in situ grain refiner and ultrasonic treatment (UT) and its influence on the mechanical properties of Mg-Sm-Al magnesium alloy. The grain size is reduced with the increasing of Al content, which is attributed to the enhancement of heterogeneous nucleation by Al2Sm particles. The ultrasonic melt treatment also refines grains via increasing the number of nucleation sites by ultrasonic cavitation. There is a maximum grain refinement efficiency on a certain solidification circumstance. The alloy-ing method (generation the in situ grain refiner) and UT have a positive interaction, which increases the number of potential nucleation particles in melt, while the number of acti-vated nucleation particles is decided by solidification condition. The increase of Al content and UT improve both yield strength and ultimate tensile strength due to grain refinement strengthening and the second phase strengthening. The UT significantly improves the elon-gation of each alloy with an increasing range of up to 312%. The de-agglomeration of second particles and increased diversity of grain orientation respond to such improvement. (C) 2020 The Authors. Published by Elsevier B.V. more...

Friction stir processing (FSP) is used as a secondary processing technique that has been employed to enhance the microstructure and other attributes of aluminum matrix composites (AMCs). AA6061/(0–15 wt.%) Al3Ni AMCs were created using pure nickel powder, which was added to molten aluminum. The composite was then subjected to FSP. The AMC microstructures were studied prior to and after FSP using TEM, SEM, OM, and EBSD. The cast composite showed coarse grains, segregation, pores, aggression, as well as polygonal-shaped particles. FSP made the particle distribution homogeneous. Additionally, the coarse Al3Ni particles were broken down into fine particles, and the process eliminated casting defects, for example pores. The size of the grain was significantly reduced because of the severe deformation of plastic and a pinning effect induced by the particles, which were reinforced. FSP also considerably increased the density of dislocations. The resulting microstructural changes improved ductility and tensile strength. more...

The present work deals with fractograph analysis and enhancement of mechanical prop�erties like hardness and tensile strength on Al6061-SiC reinforced composites during homogenization and artificial aging at 100, 150 and 200 ◦C. Scanning Electron Microscope, followed by high end metallography testing techniques like, SEM, XRD, EDS etc. are used in the present study for characterization analysis. Metal matrix composites having 0, 8, 10 and 12 wt.% fractions of silicon carbide grits of average 25�m size, are TIG welded using the filler material ER5356. Mechanical tests showed higher hardness and lower tensile strength for Al6061-12 wt.% SiC composite under non-homogenized and artificially aged condition owing to the presence of coarse micro-segregation of �-AlFeSi and �-Al(Fe, Mn) Si phase. Microstructure confirms dendritic segregation in non-homogenized specimen and after homogenizing, dendritic segregations are minimized leading to an improvement in hardness and tensile strength. Fracture surfaces of non-homogenized and artificially aged samples indicated the existence of shrinkage porosity and accordingly failure along the interdendritic regions. Homogenized and age hardened composites failed under combi�nation of brittle and ductile mode as evident by the presence of equiaxial fine dimples. Amongst different kinds of th recently developed composites, particle reinforced metal matrix composites have a great demand and has led to the emergence of numerous struc�tural composite materials as candidates for a wide variety of industrial applications like in marine, aerospace and automobile. Property enhancementis witnessed due to the combined effect of homogenizing and lower temperature aging. 60% escalation in ultimate tensile strength of composites aged at 200 ◦C and 90% increase in UTS of composites aged at 100 ◦C is observed when compared with as weld condition after homogenizing and aging. more...

β-FeSi2 is a promising material for thermoelectric application, especially if it can be nanostructured to decrease the lattice contribution to the thermal conductivity. It can be even more interesting if the entire chain of processes implemented to obtain it is not too time and energy consuming. In this paper we report a simple route to synthesize nano-β-FeSi2 by combining mechanical milling and reactive spark plasma sintering of Fe-Si alloys. A map of the pressure-temperature conditions using a spark plasma sintering setup was performed and shows that it is possible to obtain nano-β-FeSi2 pellets with a density above 90% using dwell times as short as 5 min. The impact, of both, the density and nanostructuring on the hardness of the β-FeSi2 pellets obtained by this process are presented as well as the impact of the thermoelectric properties of the materials. more...

International audience; The deformation mechanisms of an Nb–20Si–25Ti–6Al–3Cr–3Mo alloy deformed in compression at 1000 ◦C and at a strain rate of 10−4 s−1 have been investigated, using focused ion beam and transmission electron microscopy techniques. The initial microstructure of the alloy was constituted of a solid solution bcc Nbss matrix and of Nb5Si3 phases of β (tetragonal) and γ (hexagonal) crystallographic structures, with also hcp-Ti precipitates. As expected, the only phase which exhibited plastic deformation at 1000 ◦C was the Nbss matrix. Glide of Burgers vector b = 1/2 dislocations has been observed, in planes compatible with {112} and {123} planes, or with cross-slip in {110} planes, as classically reported in bcc structures. Conversely, climb contribution has not been evidenced, probably because of rearrangement of the climbing dislocations in sub-boundaries. Fine δ-Nb11Si4 precipitates have been detected in the samples compressed at 1000 ◦C. Interactions of the δ-Nb11Si4 precipitates with the dislocations have been observed, which can potentially lead to strengthening of the Nbss phase.; Les mécanismes de déformation d'un alliage Nb-20Si-25Ti-6Al-3Cr-3Mo déformé en compression à 1000 ◦C et à une vitesse de déformation de 10-4 s-1 ont été étudiés, en utilisant des techniques de faisceau d'ions focalisés et de microscopie électronique en transmission. La microstructure initiale de l'alliage était constituée d’une solution solide bcc à base de niobium, Nbss, formant la matrice et de phases Nb5Si3 de structures cristallographiques β (quadratiques) et γ (hexagonales), avec également des précipités hcp-Ti. Comme prévu, la seule phase qui a présenté une déformation plastique à 1000 ◦C était la matrice Nbss. Le glissement des dislocations avec un vecteur de Burgers b = 1/2 a été observé, dans des plans compatibles avec les plans {112} et {123}, ou avec un glissement croisé dans les plans {110}, comme classiquement rapporté dans les structures bcc. Inversement, la contribution à la montée n'a pas été mise en évidence, probablement en raison du réarrangement des dislocations montantes dans les sous-joints. De fins précipités de δ-Nb11Si4 ont été détectés dans les échantillons compressés à 1000 ◦C. Des interactions des précipités δ-Nb11Si4 avec les dislocations ont été observées, ce qui peut potentiellement conduire au renforcement de la phase Nbss. more...

In this work, we investigated the influence of composition on the polycrystalline structure, elastic properties and fracture strength, of ZrxSi1-x, NbxSi1-x, and MoxSi1-x free-standing thin films that were deposited by magnetron sputtering and subsequently annealed at 500 °C. Despite deviations from the stoichiometric composition, the crystalline structure of all films, except for the most Zr-rich ZrxSi1-x, corresponded to their respective stoichiometric disilicide structures, without the formation of a second-phase. Off-stoichiometry was found to be accompanied by the presence of lattice defects and a decrease of the grain size, which bring about a lower tensile stress in the films. The dependence of the fracture strength on the composition was remarkably similar for the three silicides, with the lowest and highest strength values occurring for samples with 30% and 37–40% of metal content, respectively. The observed dependence of strength on composition was attributed to the combination of the Hall-Petch effect, changes in the morphology and strength of grain boundaries, and the enhancement of crystal plasticity due to lattice defects induced by off-stoichiometry. more...

The structure of the new ternary eutectic Al-Ca-Cu system considered as a replacement for the ternary eutectic system Al-Ce-Cu widely used for additive manufacturing has been studied using experimental techniques. The liquidus projection of the Al-Ca-Cu system in the aluminum corner has been suggested based on experiential studies of the microstructure and phase composition of model alloys. The suggested structure of the diagram has two quasi-binary sections: (Al)-Al27Ca3Cu7 and (Al)-Al8CaCu4 and three invariant eutectic transformations: L→(Al) + (Al,Cu)4Ca + Al27Ca3Cu7 (at 5.6 wt.% Ca, 4.5 wt.% Cu, 595 °C), L→(Al) + Al27Ca3Cu7 + Al8CaCu4 (at 2.2 wt.% Ca, 13.5 wt.% Cu, 594 °C) and L→(Al) + Al8CaCu4 + Al2Cu (at 0.5 wt.% Ca, 34 wt.% Cu, 544 °C). The limit solubility of copper in aluminum solid solution (Al) at 530 °C reaches ~5.1 wt.% in the ternary phase field (Al) + Al8CaCu4 + Al2Cu and drops to ~2.4 wt.% in the (Al) + Al8CaCu4 + Al27Ca3Cu7 ternary phase field. For the example of the model ternary hypoeutectic alloys with a predominant content of the eutectic (Al,Cu)4Ca phase, it has been shown that the system is promising for designing new eutectic-type alloys with a natural composite structure. more...

Refractory metal high entropy superalloys (RSA) are being developed for high temperature structural applications. However, recently the microstructures of several RSA have been shown to be unstable, precipitating potentially deleterious intermetallic phases during prolonged exposure at elevated temperatures. For such instability to be acceptable it is necessary for the intermetallic phase formation to be sufficiently sluggish so as to not compromise alloy performance over the time scales likely to be experienced in service. However, the rate of intermetallic phase formation in RSA are not yet known. To address this issue, here, two quaternary Al-Ta-Ti-Zr refractory superalloys that contain all of the key microstructural features of more compositionally complex RSA have been studied following exposures of 1, 10 and 100 hours at temperatures between 700 and 900˚C and compared to those previously obtained following 1000 hour exposures. Critically, needles of an Al-Zr-rich intermetallic phase were observed following only 1 hour exposure at 900˚C, demonstrating rapid formation kinetics. Furthermore, the microstructures continued to coarsen from 100 to 1000 hours, indicating low morphological stability. Higher Al content increased both the prevalence of the Al-Zr-rich intermetallic phase and raised the solvus of the desirable B2 phase. Consequently, this work highlights additional challenges in RSA development for elevated temperature applications. more...

We give an overview of contributions made to the computational phase-field modelling of alloy solidification from the University of Leeds as part of the LiME project (EPSRC Advanced Manufacturing Hub in Liquid Metal Engineering). The broader look at the more salient features from our research allows the individual contributions to be seen in a wider context than can be seen from each contribution separately. We begin with a general introduction to phase-field and then reference the numerical issues that arise from the solution of the model before outlining contributions to phase-field modelling that we found most interesting or significant. These range from controlling and developing interface-width independent modelling; controlling morphology in both single and multiphase settings; generalising from single to multiphase models; and creating a thermodynamically consistent framework for modelling entropy flow and thereby postulating a temperature field consistent with the concepts of, and applicable in, multiphase and density-dependent settings. more...

Copyright: © 2022 by the authors. Manganese-bearing intermetallic compounds (IMCs) are important for ensuring adequate corrosion performance of magnesium-aluminium alloys and can be deleterious to mechanical performance if they are large and/or form clusters. Here, we explore the formation of Al-Mn IMCs in Mg-9Al-0.7Zn-0.2Mn produced by two industrial casting processes, high-pressure die casting (HPDC) and direct chill (DC) casting. As Al8Mn5 starts forming above the α-Mg liquidus temperature in this alloy, we consider its formation during melt handling as well as during casting and heat treatment. In HPDC, we focus on sludge formation in the holding pot, partial solidification of IMCs in the shot chamber, and Al-Mn IMC solidification in the die cavity. In DC casting, we focus on interactions between Al-Mn IMCs and oxide films in the launder system, Al-Mn IMC solidification in the billet, and the partial transformation of Al8Mn5 into Al11Mn4 during solution heat treatment. The results show that minimising pre-solidification in the shot sleeve of HPDC and controlling pouring and filtration in DC casting are important for ensuring small Al-Mn intermetallic particles in these casting processes. Engineering and Physical Sciences Research Council (EPSRC, UK), grant number EP/N007638/1 (the Future LiME Hub); National Natural Science Foundation of China, grant number 51904352. more...

The effect of Ta and W additions on microstructure and mechanical properties of tilt-cast Ti-45Al-5Nb-2C (at.%) alloy was investigated. Three alloys with nominal composition Ti-45Al-5Nb-2C-2X (in at.%), where X is Ta or W, were prepared by vacuum induction melting in graphite crucibles followed by tilt casting into graphite moulds. The microstructure of the tilt-cast alloys consists of the α2(Ti3Al) + γ(TiAl) lamellar grains, single γ phase, (Ti,Nb,X)2AlC particles with a small amount of (Ti,Nb,X)C, and β/B2 phase identified only in W containing alloy. The EDS analysis shows that Ta segregates into the carbide particles and reduces dissolution of Nb in both (Ti,Nb,Ta)C and (Ti,Nb,Ta)2AlC phases. The alloying with W reduces Nb content in both carbide phases and leads to stabilisation of β/B2 phase in the lamellar α2 + γ regions. The alloying with Ta and W does not affect the volume fraction of the carbide particles but influences their size and morphology. While the alloying with Ta and W has no significant effect on Vickers hardness and the indentation elastic modulus of the studied alloys, the addition of Ta affects the nanohardness and elastic modulus of the (Ti,Nb,Ta)2AlC phase. The addition of W significantly increases the Vickers microhardness of the lamellar α2 + γ regions. more...

Architectured heterogeneous metallic composites consist of two dissimilar materials with a particular focus on spatial arrangement of constituents. This experimental study describes the application of Field Assisted Sintering Technique (FAST) for manufacturing of composite materials by sintering of a bulk reinforcement with a powder metal. Simple structure made of Ti wire (Ti Grade 2) was sintered with Al6061 alloy powder at 560 &deg, C for 10 min. Successful material bonding and evolution of diffusion layer was thoroughly studied by scanning and transmission electron microscopy. Diffusion layer and adjacent precipitates are described as ternary Ti-Al-Si &tau, 1 and &tau, 2 phases. Si, as an alloying element in the Al6061 alloy, significantly affects the formation of the diffusion layer at the material interface due to its high inter-diffusion coefficient in both Al and Ti. Detailed TEM analysis also showed a modulated &tau, 1/&tau, 2 structure resembling a long-period stacking order (LPSO) phase, which has not been previously reported in the Ti-Al-Si ternary compounds. FAST is capable to manufacture composites from dissimilar constituents, which opens new possibilities for design and manufacturing of architectured materials. more...

This work demonstrates precision control of hydrogen content in La(Fe,Co,Si)13Hδ for the development of environmentally friendly magnetocaloric-based cooling technologies, using an electrolytic hydriding technique. We show the Curie temperature, a critical parameter which directly governs the temperature window of effective cooling, can be varied easily and reproducibly in 1 K steps within the range 274 K to 402 K. Importantly, both partially (up to 10%) and fully hydrided compositions retain favorable entropy change values comparable to that of the base composition. Crucially, we show in these second-order phase transition compounds, partial hydriding is stable and not susceptible against phase separation. more...

There remains some disagreement in the literature on CeTiGe over the presence of a structural transition from the low temperature CeFeSi-type form to the high temperature CeScSi-type structure. We present a detailed study of the effect of temperature on this structural transition. Furthermore, the same hydride is obtained after hydrogenation of both forms. Using neutron powder diffraction we find that the structure of CeTiGeH 1.5 corresponds to a stuffed variant of the CeScSi-type structure with space group I 4 /mmm , a = 4.0785(1) A and c = 17.1060(8) A. The H atoms occupy both the Ce 4 tetrahedral sites and the Ti 4 Ce square based pyramidal sites for a total hydrogen occupancy of 1.5 H f.u. −1 . Preliminary examinations of the magnetic properties after hydrogenation reveal the onset of low temperature magnetic order around 3.5 K, suggesting for the first time a hydrogen induced magnetic order for an intermetallic with CeScSi-type structure. more...

High purity CoSb3, Ni0.06Co0.94Sb3 and In0.13Co4Sb12 were synthesized from oxides by magnesioreduction. This novel synthesis route to CoSb3-based skutterudites directly yields highly crystalline powders with submicronic grain size. Densified mesostructured pellets with an average grain size ranging between 550 and 800 nm were obtained by spark plasma sintering. The strong phonon scattering induced by the mesostructuration leads to a lattice thermal conductivity reduction up to 25% for CoSb3 and Ni0.06Co0.94Sb3 at 300 K without significantly degrading the electronic properties. Consequently, maximum ZT figures-of-merit of 0.09, 0.60 and 0.75 are found for CoSb3, Ni0.06Co0.94Sb3 and In0.13Co4Sb12, respectively, showing the ability of this scalable process to reach the best performances reported in literature for these compositions at moderate temperature and annealing duration. more...

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 20/03/2021 The interfacial reaction of Sn-8Zn-3Bi-xSb (x = 0, 0.5, 1.0, 1.5) on Cu substrate has been investigated under 150 °C thermal aging up to 720 h and an interfacial reaction mechanism, which governs the aging process, has been proposed. A 1 μm thin layer of scallop-shaped ε-CuZn5 intermetallic compounds (IMCs) and a 4 μm thin layer of planar γ-Cu5Zn8 IMCs were formed at the interface after solder reflow. During initial aging, ε-CuZn5 transformed to γ-Cu5Zn8 and the intermetallic layer (IML) at the interface thickened. As aging prolonged, Cu5Zn8 started to degrade due to the depletion of Zn and voids formed throughout the IML. These voids were rapidly filled by diffusing Sn atoms, inducing a tunnelling effect, allowing Sn to reach the Cu substrate and form Cu6Sn5 IMCs at the interface. The thickening of the IML is controlled by a diffusion mechanism and this is suppressed by introducing Sb as a micro-alloying component, hypothetically though the pinning effect to reduce the diffusion rate of Zn in Sn matrix. peer-reviewed more...

The intermetallic compounds Zr2Pd and ZrPd2 have been investigated by perturbed angular correlation (PAC) spectroscopy considering anomalies in their hydrogen absorption properties. It is known that both these compounds have same crystal structure, but Zr2Pd forms an excellent hydride while ZrPd2 does not, even at high pressure. From PAC measurement at room temperature in annealed ZrPd2 sample, this phase is found as a minor component (∼27%) while the dominating phase is identified to be the ZrPd3 (∼73%). In Zr2Pd, this phase has been found to be predominant (∼86%) along with a minor phase (∼14%) due to ZrPd. In ZrPd2, unlike Zr2Pd, a weak temperature dependence of electric field gradient (EFG) has been found from present PAC measurements. Also, site occupancies for both Zr and Pd atoms by the Ta-probe atoms have been found in ZrPd2 and ZrPd3 (formed in ZrPd2). In ZrPd3, Pd site occupancy by the probe is found to be maximum while a small fraction for Zr site occupancy has been found. But, in case of Zr2Pd and ZrPd, no Pd site occupancy of the probe is observed. Calculation of electric field gradients at 181Ta impurity atom for different phases have been performed by density functional theory based on the all electron full potential linearized augmented plane wave plus local orbitals (FP-(L)APW + lo) method to assign the different components observed from PAC measurements. Measurements by XRD have also been carried out to confirm the presence of component phases in the samples. more...

International audience; We determine the magnetic structures of HoFe6Sn6-type (Immm) YbMn6-yFeySn6 alloys (y = 0.25, 0.50, 0.75 and 1.00) from powder neutron diffraction experiments. The valence state and local magnetism of Yb are investigated using X-ray Near Edge Spectroscopy (XANES) and X-ray Magnetic Circular Dichroism (XMCD) at the Yb L3 edge. The mean Yb valence decreases upon Fe doping (from υ ~ 2.66 down to υ ~ 2.46) and there is no 4f Yb magnetism throughout the series. The Fe for Mnsubstitution leads to change in the spins arrangement of the 3d sublattice by reinforcing antiferromagnetic exchange interactions without significant change in T = Mn/Fe moment magnitude (m ~ 2.35 µB). The ground state of the alloy with y = 0.25 is ferromagnetic whilst Fe richer alloys are helimagnets with wave-vector k = 0, qy, 0. The turn-angle increase upon Fe doping manifests by a mitigation of the Yb L3 dichroic effect, solely due to hybridization between its 5d states and the selfpolarized 3d states of T. more...

The effects of cooling rate and annealed temperature on the state of atomic order and microstructure of L21 domains of Ni45Co5Mn36.6In13.4 ribbons are investigated comprehensively. The state of atomic order is quantitatively studied by in situ X-ray diffraction (XRD), and the microstructure of ordered domains is revealed by transmission electron microscopy (TEM). As-spun ribbons show B2 structure of low atomic order, exhibiting the dispersive L21 domains’ morphology. By applying heat treatment around the order–disorder transition temperature followed by furnace cooling or quenching into water, respectively, we found the strong dependence of ordered domains on cooling rates. Furnace cooling samples show L21 domains with small sized antiphase boundary, revealing a high degree of atomic order, while quenching hinders the formation of ordered domains. Annealing above the order–disorder transition temperature followed by quenching preserves the disordered atomic state with the mixture of L21 structure in B2 matrix. more...

Magnetic intermetallic compounds based on rare earth elements and 3d transition metals are widely investigated due to the functionality of their physical properties and their variety of possible applications. In this work, we investigated the features of the electronic structure and magnetic properties of ternary intermetallic compounds based on gadolinium GdMn1-xTixSi, in the framework of the DFT + U method. Analysis of the densities of electronic states and magnetic moments of ions in Ti-doped GdMnSi showed a significant change in the magnetic properties depending on the contents of Mn and Ti. Together with the magnetic moment, an increase in the density of electronic states at the Fermi energy was found in almost all GdMn1-xTixSi compositions, which may indicate a significant change in the transport properties of intermetallic compounds. Together with the expected Curie temperatures above 300 K, the revealed changes in the magnetic characteristics and electronic structure make the GdMn1-xTixSi intermetallic system promising for use in microelectronic applications. more...

There is a growing interest in laser melting processes, e.g., for metal additive manufacturing. Modelling and numerical simulation can help to understand and control microstructure evolution in these processes. However, standard methods of microstructure simulation are generally not suited to model the kinetic effects associated with rapid solidification in laser processing, especially for material systems that contain intermetallic phases. In this paper, we present and employ a tailored phase-field model to demonstrate unique features of microstructure evolution in such systems. Initially, the problem of anomalous partitioning during rapid solidification of intermetallics is revisited using the tailored phase-field model, and the model predictions are assessed against the existing experimental data for the B2 phase in the Ni-Al binary system. The model is subsequently combined with a Potts model of grain growth to simulate laser processing of polycrystalline alloys containing intermetallic phases. Examples of simulations are presented for laser processing of a nickel-rich Ni-Al alloy, to demonstrate the application of the method in studying the effect of processing conditions on various microstructural features, such as distribution of intermetallic phases in the melt pool and the heat-affected zone. The computational framework used in this study is envisaged to provide additional insight into the evolution of microstructure in laser processing of industrially relevant materials, e.g., in laser welding or additive manufacturing of Ni-based superalloys. more...