Papers by Keyword: Intermetallic

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Authors: Sergey M. Zharkov, Roman R. Altunin, Evgeny T. Moiseenko, Galina M. Zeer, Sergey N. Varnakov, Sergey G. Ovchinnikov
Abstract: Solid-state reaction processes in Fe/Si multilayer nanofilms have been studied in situ by the methods of transmission electron microscopy and electron diffraction in the process of heating from room temperature up to 900ºС at a heating rate of 8-10ºС/min. The solid-state reaction between the nanolayers of iron and silicon has been established to begin at 350-450ºС increasing with the thickness of the iron layer.
Authors: E.E. Kokorina, M.V. Medvedev, I.A. Nekrasov
Abstract: Intermetallic compounds R2Fe17 are perspective for applications as permanent magnets. For the practical usage, these systems must have the Curie temperature Tc much higher than room temperature and, preferably, an easy axis anisotropy. Nowadays, the highest Tc among the stoichiometric R2Fe17 materials is 476 K, which is not sufficient. There are two possibilities to increase Tc: substitution of Fe ions with non-magnetic elements or introduction of light elements into interstitial positions. In this work we have focused our attention on the substitution scenario of rising the Curie temperature, which was observed experimentally in the Gd2Fe17-xGax (x=0, 3, 6) compounds. In the framework of the LSDA approach the electronic structure and magnetic properties of the compounds were calculated. Ab initio exchange-interaction parameters for all nearest Fe ions in the Fe sublattice were obtained. Employing the theoretical values of exchange parameters, the Curie temperatures Tc of Gd2Fe17-xGax were estimated within the mean-field theory. The obtained values of Tc agree well with experiment. Also the LSDA computed values of total magnetic moment coincide with the experimental ones.
Authors: Sundaram Kumar, Sam Agarwal, Keyna O'Reilly
Abstract: Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al3Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al3Nb. The in-situ formed Al3Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al3Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.
Authors: M.A.A. Mohd Salleh, A. Sugiyama, Hideyuki Yasuda, Stuart D. McDonald, Kazuhiro Nogita
Abstract: This paper demonstrates the development of an experimental technique of in-situ observation for soldering of Sn-0.7wt%Cu lead-free solder on a Cu substrate which was achieved for the first time by synchrotron X-ray imaging. Reactions between liquid solder and Cu substrate during a soldering process were able to be recorded in real-time. Individual stages of the soldering process consisted of flux activation in removal of Cu oxide, solder melting and contact with the Cu substrate (wetting) and intermetallic compound (IMC) and void formation between the solder and Cu substrate. The technique development which includes experimental setup with calculated optimum beam energy in the range of 20 – 30 keV appears to result in a clear observation of real-time X-ray imaging of the soldering process. This technique provides a key method to understand the mechanism of formation of micro-electronic inter-connects for future electronic packaging applications.
Authors: Joël Bonneville, Christophe Coupeau, Dimitri Charrier
Abstract: The positive temperature dependence of flow stress in Ni3Al is examined through fine slip trace analysis performed by atomic force microscopy. Slip traces, which result from dislocation movements, constitute outstanding markers for investigating the elementary dislocation mechanisms that control plasticity. The experiments were performed on two Ni3Al-base alloys, with Ta or Hf as additional elements. The results give evidence that the anomaly domain is accompanied by a drastic exhaustion of mobile dislocations and very short cross-slip distances on the cube cross-slip plane.
Authors: Alain Jacot, Amin Rostamian
Abstract: A phenomenological modeling approach has been developed to describe the massive transformation and the formation of lamellar microstructures during cooling in gamma titanium aluminides. The modeling approach is based on a combination of nucleation and growth laws which take into account the specific mechanisms of each phase transformation. Nucleation of both massive and lamellar γ is described with classical nucleation theory, accounting for the fact that nuclei are formed predominantly at α/α grain boundaries. Growth of the massive γ grains is calculated with a mathematical expression for interface-controlled reactions. A modified Zener model is used to calculate the thickening rate of the γ lamellar precipitates. The model incorporates the effect of particle impingement and rapid coverage of the nucleation sites due to growth. The driving pressures of the phase transformations are obtained form Thermo-Calc based on actual temperature and matrix composition. The model permitted investigating the influence of alloy chemistry, cooling rate and average α grain size upon the amount of massive γ and the average thickness and spacing of the lamellae. Calculated CCT diagrams were compared with experimental data collected from the literature and showed good agreement.
Authors: Ming Liu, Sandrine Zanna, Helene Ardelean, Isabelle Frateur, Patrik Schmutz, Guang Ling Song, Andrej Atrens, Philippe Marcus
Abstract: An XPS investigation was carried out on the surface film formed by exposure to high-purity water, on mechanically polished Mg and the two Mg-Al intermetallic compounds: Al3Mg2 and Mg17Al12. The result for mechanically polished pure Mg indicates that a film of MgO covered by a Mg(OH)2 layer, formed by the reaction of MgO with water vapour in the air. On immersion in distilled water, this film was hydrated to a duplex film with an inner MgO layer next to the Mg metal and an external porous layer of hydroxide. For both intermetallics, there was preferential dissolution of magnesium from the mechanically ground surface and also during aqueous immersion. After immersion, there was a 10 nm thick, stable film on the surface; the film composition on Al3Mg2 was whilst that on Mg17Al12 was .
Authors: Seiichi Muneki, Hiroshi Okubo, Fujio Abe
Abstract: In order to improve the creep strength of the heat resistant steels at elevated temperatures over 700°C, a new attempt has been demonstrated using carbon and nitrogen free Fe-Ni martensitic and austenitic alloys strengthened by Laves phase such as Fe2W and Fe2Mo. It is important that these alloys are independent of any carbides and any carbo-nitrides as strengthening factors. The high temperature creep tests over 700°C exceed 36,000 hours and the test is continued. Creep behavior of alloys is found to be completely different from that of the conventional high-Cr ferritic steels. The alloys exhibit gradual change in the creep rate with strain both in the transient and acceleration creep regions, and give a larger strain for the minimum creep rate. Effect of Cr on the Fe-12Ni-9Co-10W alloys on the creep properties more over 700°C was investigated. It became clear that the value for 100,000 hours was exceeded at 700°C and 100MPa calculated from the Larson-Miller parameter at C=20. And surface appearance of crept specimen was investigated in detail.
Authors: Svea Mayer, Michael Kastenhuber, Helmut Clemens
Abstract: Intermetallic TiAl alloys based on the γ-TiAl phase are already used as engineering light-weight high-temperature materials in aircraft and automotive engines. Thereby, they partly substitute the twice as heavy Ni-base superalloys. Present applications are, for example, blades in the low-pressure turbine of advanced aero-engines, turbine wheels for turbocharger systems of car diesel engines as well as engine parts used in racing cars. All these applications require balanced mechanical properties, i.e. certain ductility at room temperature as well as defined creep strength at elevated temperatures. The first part of this paper reviews the alloy design strategy, which was used for the development of a β-solidifying γ-TiAl-based alloy, the so-called “TNM alloy”, which exhibits an excellent hot-deformability. In the meantime, the TNM alloy with the nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in atomic percent, at.%) is introduced in a particular eco-friendly and fuel-saving aero-engine, which is powering a medium-range aircraft since the beginning of 2016. In the second part of this work the microstructural parameters are highlighted, which influence the failure strain at room temperature and creep strength at elevated temperatures. It will be shown how the creep resistance can be improved by tailoring phase fractions as well as the spatial arrangement of the microstructural constituents.
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