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  • 1. Achanta, S.
    et al.
    Feuerbacher, M.
    Grishin, Alexander
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Ye, X.
    Celis, J. -P
    On the mechanical and tribological behavior of Al3Mg2 complex metallic alloys as bulk material and as coating2010Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 18, nr 11, s. 2096-2104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New materials with tunable physical, mechanical, chemical, and thermal properties are attractive for many applications and stand as prospective substitutes for the existing engineering materials. In that respect, complex metallic alloys (CMA) have recently demonstrated promising traits where a myriad of physical, mechanical, chemical properties can be obtained by altering the structure. CMA's have a large crystal size with thousands of atoms per unit cell. In this work, some mechanical properties and tribological behavior of Al3Mg2 based CMA are discussed. The surface characterization, deformation mode, mechanical and tribological properties of bulk and thin film Al3Mg2 materials are investigated, and compared with existing engineering materials. The results revealed a contrasting tribological behavior of Al3Mg2 when used as either bulk material or as coating. Al3Mg2 coatings act as a low friction solid lubricant under certain conditions, with a coefficient of friction comparable to that of diamond-like carbon coatings. It is suggested that the quasi-crystalline nature of Al3Mg2-coatings renders the surface stiff and that the characteristics of the wear debris generated are responsible for the low friction behavior.

  • 2.
    Babu, Prasath
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Indian Institute of Science, Bangalore, India.
    Vamsi, K. V.
    Karthikeyan, S.
    On the formation and stability of precipitate phases in a near lamellar γ-TiAl based alloy during creep2018Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 98, s. 115-125Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The formation, evolution and stability of metastable phases observed in the γ-TiAl based alloy Ti-47Al-2Cr-2Nb was studied under creep deformation with stress applied at two different hard orientations in a highly textured as-cast + HIPed material. Previously we have reported that the metastable phase Ti(Al,Cr)2 with C14 Laves phase structure forms at the γ-α2 interface which acts as sink for the alloying elements ejected from the dissolving α2 phase and also expected to effectively control the interface stresses through short range diffusion and modifications in the chemical composition [1]. Ab initio density functional theory based calculations were carried out to evaluate the effect of choice of lattice position and site occupancy of aluminium atoms in the Ti(Al,Cr)2 structure on the lattice parameter variation and thermodynamic stability. C14 with the composition 25 at. % Al was found to have lattice parameter values close to the inter-planar spacing of <110>γ and <10-10>α2 which would have a lower misfit with C14 across the interface. From the cohesive energy calculations, Laves phase C14 with a constrained lattice parameter due to the adjoining phases, exhibits higher stability than the B2 and L10 structures across a range of compositions studied. Electron diffraction simulations of C14 with a composition of 25% Al compared with the experimental data suggest that the structure C14 has taken up either a random site occupancy compared to a specific choice of ordering to minimize the interfacial stress. Though the experimental evidences do not strongly support a long-range ordering theory in C14, short-range ordering could be a tangible choice for alleviating interface misfits. The ability of C14 to assume different lattice parameters at and far from the α2-γ interface also suggest that the C14 acts as buffer layer between α2 and γ phases in the presence of local stresses, although this is not the thermodynamically expected phase at the temperature of creep experiment.

  • 3. Fernandes, P. B.
    et al.
    Coelho, G. C.
    Ferreira, F.
    Nunes, C. A.
    Sundman, Bo
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Thermodynamic modeling of the Nb-Si system2002Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 10, nr 10, s. 993-999Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optimized coefficients of the Gibbs free energy expression for each stable phase of the binary Nb-Si have been obtained, using the Thermo-Calc program for this purpose. The Nb3Si, alphaNb(5)Si(3), NbSi2 and Diamond (Si) have been modeled as stoichiometric phases and the liquid L, BCC (Nb) and the betaNb(5)Si(3) phases as solutions, with the excess term described using the Redlich-Kister formalism. The Si solubility in the betaNb(5)Si(3) phase has been modeled according to two possibilities: (i) Si substituting for Nb and (ii) vacancies in the Nb positions. The calculated diagrams compare well with the experimental information taken from the literature.

  • 4.
    Gu, Ziyan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Deevi, S. C.
    Macroscopic and Local Strain-induced Ferromagnetism at a Micron-scale in FeAl Cold Rolled sheets2005Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216Artikel i tidskrift (Övrigt vetenskapligt)
  • 5. He, J. Y.
    et al.
    Wang, H.
    Wu, Y.
    Liu, X. J.
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nieh, T. G.
    Lu, Z. P.
    Precipitation behavior and its effects on tensile properties of FeCoNiCr high-entropy alloys2016Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 79, s. 41-52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we present a systematic study on the precipitation behavior and mechanical properties of a FeCoNiCr-based high-entropy alloy alloyed with dilute amounts of Ti and Al, (FeCoNiCr)(100-x-y)TixAly (where x = 1-3, y = 4-9 at.%). It was found that, upon aging, nano-sized L1(2)-Ni-3(Ti, Al) particles are formed within grains, whilst L2(1)-(Ni, Co)(2)TiAl Heusler particles are formed mainly along grain boundaries. The relative thermal stability of the two phases were studied at different aging temperatures (700-900 degrees C) with various durations of time (up to 48 h) and the results were directly compared with Thermo-talc calculations. Tensile tests were also conducted on alloys aged under different conditions. The measured properties, including strength and ductility, were correlated with the microstructure of aged (FeCoNiCr)(100-x-y)TixAly alloys, with particular attention on the distribution and morphology of the two kinds of precipitate. Whereas both phases could contribute to the strengthening of the alloys via either Orowan bowing or particle shearing mechanism, the brittle (Ni, Co)(2)TiAl Heusler phase was found to mainly affect the tensile plasticity. A simple composite model was proposed to describe the plastic strain of alloys. Based on observed microstructure and its corresponding mechanical performance, the alloy with the composition of (FeCoNiCr)(94)Ti2Al4, when aged between 700 and 800 degrees C, gives the best balanced strength/ductility properties.

  • 6.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Eriksson, Olle
    Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ; Wigner Res Ctr Phys.
    Mapping the magnetic transition temperatures for medium- and high-entropy alloys2018Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 95, s. 80-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tailorable magnetic state near room temperature is very promising for several technological, including magnetocaloric applications. Here using first-principle alloy theory, we determine the Curie temperature (T-C) of a number of equiatomic medium- and high-entropy alloys with solid solution phases. All calculations are performed at the computed lattice parameters, which are in line with the available experimental data. Theory predicts a large crystal structure dependence of T-C, which explains the experimental observations under specified conditions. The sensitivity of the magnetic state to the crystal lattice is reflected by the magnetic exchange interactions entering the Heisenberg Hamiltonian. The analysis of the effect of composition on T-C allows researchers to explore chemistry-dependent trends and design new multi-component alloys with pre-assigned magnetic properties.

  • 7. Pecanha, Rockfeller Maciel
    et al.
    Ferreira, Flavio
    Coelho, Gilberto Carvalho
    Nunes, Carlos Angelo
    Sundman, Bo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Thermodynamic modeling of the Nb-B system2007Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 15, nr 8, s. 999-1005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, the Nb-B binary system was thermodynamically optimized. The stable phases in this system are BCC (niobium), Nb3B2, NbB, Nb3B4, Nb5B6, NbB2, B (boron) and liquid L. The borides Nb3B2, NbB, Nb3B4 and Nb5B6 and the B (boron) were modeled as stoichiometric phases and the liquid L, BCC (niobium) and NbB2 as solutions, using the sublattices model, with their excess terms described by the Redlich-Kister polynomials. The Gibbs energy coefficients were optimized based on the experimental values of enthalpy of formation, low temperature specific heat, liquidus temperatures and temperatures of invariant transformations. The calculated Nb-B diagram reproduces well the experimental values from the literature.

  • 8.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Isaev, E. I.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio calculations of elastic properties of Pt-Sc alloys2008Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 16, nr 8, s. 982-986Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Elastic properties of substitutionally disordered Pt-rich Pt-Sc alloys and L1(2)-ordered Pt3Sc compound are derived from the first-principles calculations based on the exact muffin-tin orbitals (EMTO) method. We demonstrate that these alloys should exhibit a ductile behavior, which combined with relatively high melting temperature and strong cohesive properties make them a very promising candidate for high-temperature applications.

  • 9.
    Teng, Lidong
    et al.
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Aune, Ragnhild
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Seetharaman, Seshadri
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Study of Mn activities in Mn-Ni-C alloys by EMF measurements2003Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 11, nr 11-12, s. 1229-1235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     The activities of manganese in Mn-Ni-C alloys have been studied by solid-state galvanic cell technique with CaF2 as the solid electrolyte. The measurements of electromotive force (EMF) have been carried out in the temperature range 920-1240 K. The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). It was established that the substitution of Mn by Ni in the (MnNi)(23)C-6 carbide was limited, that the lattice parameter decreased slightly with increase in the Ni content and that a solid solution is formed between Mn and Ni. It was also found that the activity of manganese decreases with increase in the nickel content when the ratio of C/(Mn+C) is less than 8.3 wt.%, and that the negative effect of Ni on the activity of Mn in Mn-Ni-C ternary system decreases as the carbon content increases. However, when the ratio of C/(Mn+C) is equal to 8.3 wt.% or more, the activity of manganese is independent of the nickel content.

  • 10.
    Tian, Fuyang
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. University of Science and Technology Beijing, China.
    Varga, Lajos K.
    Chen, Nanxian
    Shen, Jiang
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Empirical design of single phase high-entropy alloys with high hardness2015Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 58, s. 1-6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We collect the available basic properties of nearly 100 high-entropy alloys (HEAs) with a single face centered cubic (fcc) or body centered cubic (bcc) phase. HEAs crystallizing in the fcc structure are mainly composed of the late 3d elements (LTM-HEAs), whereas HEAs consisting of the early (refractory) transition elements and the LTM-HEAs containing an increased level of bcc stabilizer form the bcc structure. Guided by the solid solution theory, we investigate the structure and hardness of HEAs as a function of the valence electron concentration (VEC) and the atomic size difference (delta). The fcc structure is found for VEC between 7.80 and 9.50, whereas the structure is bcc for VEC between 4.33 and 7.55. High strength is obtained for an average valence electron number VEC similar to 6.80 and for an average atomic size difference delta approximate to 6%. Based on these empirical correlations, one can design the high-entropy alloys with desired hardness.

  • 11. Xiong, Wei
    et al.
    Du, Yong
    Lu, Xiaogang
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schuster, Julius Clemens
    Chen, Hailin
    Reassessment of the Ce-Ni binary system supported by key experiments and ab initio calculations2007Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 15, nr 11, s. 1401-1408Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Ce-Ni system is reassessed by means of CALPHAD (CALculation of PHAse Diagram) approach, supplemented with decisive experiments and enthalpies of formation computed via VASP (Vienna ab initio simulation package) code. Fourteen alloys are prepared in order to check the general feature of the established Ce-Ni phase diagram and to provide new phase diagram data for the refinement of previous modeling. The phase identification for both as-cast and annealed states is performed by means of X-ray diffraction technique, and the phase transition temperatures are measured by differential thermal analysis. Electron probe microanalysis is employed to determine two tie lines between CeNi5 and (Ni). The enthalpies of formation for CeNi2 and CeNi5 are calculated using VASP code with a desire to clarify the discrepancies among the literature data. A set of self-consistent thermodynamic parameters for the Ce-Ni system are finally obtained. Significant improvements have been made, compared with the previous assessments.

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