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  • 1.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Askari, Syed Javid
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Shah, Khadijah Ali
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Du, Xueli
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Microstructure, mechanical properties, electrical conductivity and wear behavior of high volume TiC reinforced Cu-matrix composites2009In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 60, no 4, p. 327-336Article in journal (Refereed)
    Abstract [en]

    This study deals with the processing, microstructure, mechanical properties, electrical conductivity and wear behavior of high volume titanium carbide reinforced copper matrix composites. The microstructural study revealed that the titanium carbide particles were distributed uniformly in the matrix phase. No interface debonding and micro-cracks were observed in the composite. The addition of alloying elements in the copper considerably increased the sintered density and properties. The composite hardness and strength increased with titanium carbide content and alloying elements in the matrix phase. The electrical conductivities of the composites were predicted using three point upper bound and two phase self consistent predictive models. The wear resistance of the composites was studied against high speed steel. Wear mechanisms were discussed by means of microscope observations on the worn surfaces. The ratio of titanium carbide average grain size to the mean free path of the binder was introduced as a parameter to determine wear performance.

  • 2.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science, University of Science and Technology Beijing, 30 Xue Yuan Road, 100083, Beijing.
    Guo, SJ
    Institute of Powder Metallurgy, School of Materials Science, University of Science and Technology Beijing, 30 Xue Yuan Road, 100083, Beijing.
    Microstructure, mechanical and fretting wear properties of TiC-stainless steel composites2008In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 59, no 1, p. 84-90Article in journal (Refereed)
    Abstract [en]

    This study deals with the processing, microstructure, and wear behavior of TiC-reinforced stainless steel matrix composites, containing 50 to 70 wt.% TiC. Powder technology was used to successfully fabricate the composites. The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the TiC particles were distributed uniformly in the steel matrix phase. Interface debonding and microcracks were not observed in the composite. The composite hardness increased with TiC content. The fretting wear resistance of the composites was studied against high speed steel. The wear mechanisms are discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microplowing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microplowing and rapid removal of material from the wear surface was observed at high wear load. The variation of wear loss with volume fraction and mean free path of the binder phase is also reported

  • 3. Azadian, S.
    et al.
    Wei, L-Y.
    Warren, Richard
    Luleå tekniska universitet.
    Delta phase precipitation in inconel 7182004In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 53, no 1, p. 7-16Article in journal (Refereed)
    Abstract [en]

    The precipitation and dissolution kinetics of the δ-phase were studied in three wrought versions and one spray-formed (SF) version of the nickel alloy, Inconel 718. The precipitation in the spray-formed version and one wrought version was followed during isothermal ageing for up to 100 h between 700 and 1000°C. The δ-phase precipitates in the form of nonuniformly distributed thin platelets and an alternative method of measuring volume fraction of this precipitate morphology is proposed. At and above 800°C, the precipitation was measured quantitatively in terms of the volume fraction and platelet thickness distribution. The maximum rate of precipitation occurred at approximately 900°C. The solvus temperature lay between 1005 and 1015°C for Nb contents of 5.06 and 5.41 wt.%, respectively. A study was made of the dissolution of the δ-phase in all four alloys using isochronal treatments and this confirmed the above solvus temperature range. The effect of δ-phase and its dissolution on the grain growth of the alloys was also determined.

  • 4.
    Cwirzen, A.
    et al.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, K.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Nasibulin, A. G.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Kaupinen, E. I.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Mudimela, P. R.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Penttala, V.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    SEM/AFM studies of cementitious binder modified by MWCNT and nano-sized Fe needles2009In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 60, no 7, p. 735-740Article in journal (Refereed)
    Abstract [en]

    Several compositions of cement paste samples containing multiwalled carbon nanotubes were produced using a small-size vacuum mixer. The mixes had water-to-binder ratios of 0.25 and 0.3. Sulfate resistant cement has been used. The multiwalled carbon nanotubes were introduced as a water suspension with added surfactant admixtures. The used surfactant acted as plasticizing agents for the cement paste and as dispersant for the multiwalled carbon nanotubes. A set of beams was produced to determine the compressive and flexural strengths. The scanning electron microscope and atomic force microscope studies of fractured and polished samples showed a good dispersion of multiwalled carbon nanotubes in the cement matrix. The studies revealed also sliding of multiwalled carbon nanotubes from the matrix in tension which indicates their weak bond with cement matrix. In addition to multiwalled carbon nanotubes also steel wires covered with ferrite needles were investigated to determine the bond strength between the matrix and the steel wire. These later samples consisted of 15-mm-high cylinders of cement paste with vertically cast-in steel wires. As reference, plain steel wires were cast, too. The bond strength between steel wires covered with nano-sized Fe needles appeared to be lower in comparison with the reference wires. The scanning electron microscope studies of fractured samples indicated on brittle nature of Fe needles resulting in shear-caused breakage of the bond to the matrix. © 2008 Elsevier Inc. All rights reserved.

  • 5.
    Fargas, G.
    et al.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain , .
    Roa, J.J.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain.
    Sefer, Birhan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain.
    Pedersen, R.
    Division of Subtractive and Additive Manufacturing, University West, S-46186 Trollhaettan.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Matteo, A.
    CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona 08019, Spain.
    Influence of cyclic thermal treatments on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo alloy2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 145, p. 218-224Article in journal (Refereed)
    Abstract [en]

    Ti-6Al-2Sn-4Zr-2Mo is one of the most common titanium alloys for aerospace industry. This alloy experiences oxidation phenomenon at elevated temperatures. In the present study, cyclic thermal treatments were performed in air at 500, 593 and 700 °C, up to 500 cycles, in order to determine the oxidation kinetics and to analyze the oxide scale and alpha-case formation. Moreover, results were compared to those achieved under isothermal conditions to elucidate differences between both thermal conditions. In this sense, metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Field Emission Scanning Electron Microscopy and Focus Ions Beam, were used to analyze surface oxidation evolution. Results pointed out that cyclic treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed the formation of not only rutile, as isothermal treatments, but also anatase. Thickness of the oxide scale was higher for cyclic conditions, while alpha case did not exceed values reached by isothermal treatments and even became lower at 500 °C.

  • 6. Gaddam, Raghuveer
    et al.
    Sefer, Birhan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oxidation and alpha–case formation in Ti–6Al–2Sn–4Zr–2Mo alloy2015In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 99, p. 166-174Article in journal (Refereed)
    Abstract [en]

    Isothermal heat treatments in ambient air were performed on wrought Ti–6Al–2Sn–4Zr–2Mo (Ti–6242) material at 500, 593 and 700 °C for times up to 500 hours. In presence of oxygen at elevated temperatures simultaneous reactions occurred in Ti–6242 alloy, which resulted in formation of an oxide scale and a layer with higher oxygen concentration (termed as alpha–case). Total weight gain analysis showed that there was a transition in the oxidation kinetics. At 500 °C, the oxidation kinetics obeyed cubic relationship up to 200 hours and thereafter changed to parabolic at prolonged exposure times. At 593 °C, it followed parabolic relationship. After heat treatment at 700 °C, the oxidation obeyed parabolic relationship up to 200 hours and thereafter changed to linear at prolonged exposure times. The observed transition is believed to be due to the differences observed in the oxide scale. The activation energy for parabolic oxidation was estimated to be 157 kJ/mol. In addition, alpha–case layer was evaluated using optical microscope, electron probe micro analyser and microhardness tester. The thickness of the alpha–case layer was found to be a function of temperature and time, increasing proportionally, and following parabolic relationship. The activation energy for formation of alpha–case layer was estimated to be 153 kJ/mol.

  • 7. Gyhlesten Back, Jessica
    et al.
    Surreddi, Kumar
    Materials Technology, Dalarna University, Falun, Sweden.
    Microstructure analysis of martensitic low alloy carbon steel samples subjected to deformation dilatometry2019In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 157, article id 109926Article in journal (Refereed)
    Abstract [en]

    Low alloy martensitic steels are commonly used in structural and wear resistant applications due to their excellent mechanical properties and abrasion resistance. Martensite phase is generally achieved by rapid cooling, and prior deformation in the austenite region also affects the martensite transformation. It is important to understand the martensite transformation when there is deformation above Ae3. Deformation and quenching simulations have been performed using dilatometry on a low alloy carbon steel. The aim was to determine the influence of deformation above Ae3 (prior deformation) on, firstly, the austenite grain size and shape, and secondly, the martensitic microstructure and variant selection. In addition, the hardness of the martensitic structure due to prior deformation has been investigated. The experimental results obtained from electron backscatter diffraction and microhardness tests on the deformation dilatometry test samples were analysed. The orientation relationship Kurdjumov-Sachs has been used to analyse the martensitic variants. The results revealed a deeper understanding of prior austenite grain structure's effect on the martensitic transformation kinetics and its morphology. The martensite laths' misorientation interval 15–48° were used to visualise the prior austenite grain size. The martensitic lath structure is more refined due to increased prior deformation. Shorter martensite formation time promotes a single dominating packet within the prior austenite grain.

  • 8.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Division of Welding Technology, University West, Trollhättan 461 32, Sweden.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microstructural characterization and comparison of Ti-6Al-4V manufactured with different additive manufacturing processes2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 143, no SI, p. 68-75Article in journal (Refereed)
    Abstract [en]

    In this work, the microstructures of Ti-6Al-4V manufactured by different additive manufacturing (AM) processes have been characterized and compared. The microstructural features that were characterized are the α lath thickness, grain boundary α (GB-α) thickness, prior β grain size and α colony size. In addition, the microhardnesses were also measured and compared. The microstructure of shaped metal deposited (SMD) Ti-6Al-4V material showed the smallest variations in α lath size, whereas the material manufactured with laser metal wire deposition-0 (LMwD-0) showed the largest variation. The prior β grain size was found to be smaller in material manufactured with powder bed fusion (PBF) as compared with corresponding material manufactured with the directed energy deposition (DED) processes. Parallel bands were only observed in materials manufactured with DED processes while being non-present in material manufactured with PBF processes.

  • 9.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Electron backscatter diffraction characterization of fatigue crack growth in laser metal wire deposited Ti-6Al-4V2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, p. 245-256Article in journal (Refereed)
    Abstract [en]

    By additive manufacturing (AM) there is a feasibility of producing near net shape components in basically one step from 3D CAD model to final product. The interest for AM is high and during the past decade a lot of research has been carried out in order to understand the influence from process parameters on the microstructure and furthermore on the mechanical properties. In the present study laser metal wire deposition of Ti-6Al-4V has been studied in detail with regard to its fatigue crack propagation characteristics. Two specimen orientations, parallel and perpendicular to the deposition direction, have been evaluated at room temperature and at 250 °C. No difference in the fatigue crack growth rate could be confirmed for the two specimen orientations. However, in the fractographic study it was observed that the tortuosity varied between certain regions on the fracture surface. The local crack path characteristic could be related to the alpha colony size and/or the crystallographic orientation. Moreover, large areas exhibiting similar crystallographic orientation were observed along the prior beta grain boundaries, which were attributed to the wide alpha colonies frequently observed along the prior beta grain boundaries.

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