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  • 1.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    An investigation on the solid state sintering of mechanically alloyed nano-structured 90W--Ni--Fe tungsten heavy alloy2008In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 26, no 3, p. 145-151Article in journal (Refereed)
    Abstract [en]

    In this study, 90W–7Ni–3Fe heavy alloy was investigated for its microstructure development, mechanical properties and fracture behavior after solid state sintering. The nano-sized powders were synthesized by mechanical alloying (MA). The microstructure of solid state sintered heavy alloys consisted of tungsten matrix. The average tungsten grain size in the range of 1.7–3.0 μm was obtained. It was found that the grain size largely affected the mechanical properties. Tensile strength more than 1200 MPa was achieved at a sintering temperature of 1350 °C. Fracture mechanisms based on microscopical observations on the fracture surfaces were studied. Matrix failure, tungsten-intergranular cleavage and tungsten–matrix interfacial separation were found to be the possible failure mechanisms.

  • 2.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Humail, Islam S
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Askari, SJ
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tian, Jianjun
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shiju, Guo
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC--(W, Ti, Ta) C--6wt% Co cemented carbides2007In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 25, no 5-6, p. 405-410Article in journal (Refereed)
    Abstract [en]

    This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.

  • 3.
    Feng, Peizhong
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Humail, Islam S
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Qu, Xuanhui
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Mechanically activated reactive synthesis of refractory molybdenum and tungsten silicides2008In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 26, no 3, p. 173-178Article in journal (Refereed)
    Abstract [en]

    In this study, processing of elemental powders mixtures was carried out by mechanical alloying (MA) and heat treatment in vacuum at 700–1000 °C for 1 h. The phase transformation of the powders was investigated by X-ray diffractometer (XRD). The results showed that mechanical alloying promoted the formation of a solid solution of elemental powders. The energy stored in the powders was increased as a result of exterior energy and the barrier energy of the formation of the compound could be exceeded easily. Intermetallics of MoSi2, WSi2, Mo5Si3, Mo3Si and SiC/MoSi2 composite powders were synthesized by mechanically activated reactive synthesis (MARS). The mechanically induced self-sustaining reaction was observed in MoSi2 and MoSi2 + 10 wt%SiC stoichiometry system. It has concluded that mechanically activated reactive synthesis is an effective method for the preparation of high melting-point refractory compounds.

  • 4. Hardell, Jens
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of surface engineered tool steel at elevated temperatures2010In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 28, no 1, p. 106-114Article in journal (Refereed)
    Abstract [en]

    Tribological components operating at elevated temperatures can experience high wear, oxidation, thermal fatigue and changes in mechanical properties. In this work, the friction and wear characteristics of plasma nitrided and surface coated (CrN and TiAlN) tool steel during sliding against AISI52100 bearing steel have been studied at room temperature and 400 oC respectively using a ball on disc machine. Surface profiler and SEM/EDS techniques were used to characterise the surface topography and resulting surface damage of the test specimens. The results show that the friction of plasma nitrided tool steel during sliding against bearing steel ball is very high at room temperature and it drastically drops at 400oC. The wear is mainly abrasive at room temperature and adhesive at elevated temperatures. In case of CrN coated tool steel the friction is high but its wear is negligible at room temperature. At 400oC, the friction decreases marginally and transfer of bearing steel to the coated CrN coated disc has been observed. The TiAlN coating has shown relatively lower friction, compared to CrN and negligible wear at room temperature. At 400oC, the friction is very high and unstable and transfer of TiAlN coating to the mating ball occurs.

  • 5.
    Humail, Islam S
    et al.
    School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing.
    Akhtar, Farid
    School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing.
    Askari, Syed Jawaid
    School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing.
    Tufail, M
    School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing.
    Qu, Xuanhui
    School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing.
    Tensile behavior change depending on the varying tungsten content of W--Ni--Fe alloys2007In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 25, no 5-6, p. 380-385Article in journal (Refereed)
    Abstract [en]

    Tungsten heavy alloys (WHAs) are metal–metal composites consisting of nearly pure spherical tungsten particles embedded in a Ni–Fe–W or Ni–Co–W or Ni–Cu–W ductile matrix. In this dual phase alloy, there are several complicated relations between the ductile matrix and hard tungsten particles. The aim of this research was to examine the effect of varying tungsten content on the microstructure and mechanical properties of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity and solid volume fraction) were measured and were found to have a significant effect on the mechanical properties of tungsten-based heavy alloys. The result shows that the binding strength between the W and the matrix phase has a major influence on the ductility of tungsten-based alloys. The larger this binding force is, the better the ductility is.

  • 6.
    Larsson, C.
    et al.
    Linköping universitet.
    Odén, Magnus
    X-ray diffraction determination of residual stresses in functionally graded WC-Co composites2004In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 22, no 4-5, p. 177-184Article in journal (Refereed)
    Abstract [en]

    X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC–Co composite. Stresses were measured in both WC and Co phases at various depths. Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. For WC, the in-plane compressive residual stresses varied approximately between −300 and −500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The microstresses in the graded zone were attributed to the thermal mismatch between the WC and the Co phase during cooling from the liquid phase sintering temperature (1450 °C). The microstresses determined were in reasonable agreement with a prediction using Eshelby theory. The compressive macrostresses were attributed to the compositional gradient, a result further substantiated by the fact that no significant macrostresses were measured in a comparable homogeneous sample, i.e., without the compositional gradient. Thus, varying compositional gradients in WC–Co composites during fabrication can be expected to directly influence the macrostress component of the overall residual stress state.

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