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  • 1.
    Abadei, S
    et al.
    Chalmers University of Technology.
    Gevorgian, S
    Chalmers University of Technology.
    Cho, C.-R
    Royal Institute of Technology.
    Grishin, A.
    Royal Institute of Technology.
    Andreasson, Johanna
    Lindbäck, Ture
    DC field dependent properties of Na0.5K0.5NbO₃/SiO₂/Si structures at millimeter-wave frequencies2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 78, no 13, 1900-1902 p.Article in journal (Refereed)
    Abstract [en]

    Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 μm. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices

  • 2.
    Abadei, S.
    et al.
    Chalmers University of Technology, Department of Microelectronics.
    Gevorgian, S.
    Chalmers University of Technology, Department of Microelectronics.
    Kugler, V.
    Department of Physics, Linköping University.
    Helmersson, U.
    Department of Physics, Linköping University.
    Andreasson, Johanna
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Microwave properties of tunable capacitors basee on magnetron sputtered ferroelectric Na0.5K0.5NbO3 film on low and high resistivity silicon substrates2001In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 39, no 1-4, 359-366 p.Article in journal (Refereed)
    Abstract [en]

    In this work, small signal DC voltage dependent dielectric permittivity, loss tangent, and tuneability of magnetron sputtered epitaxial Na0.5K0.5NO3 films are studied experimentally. (100)-oriented Na0.5K0.5NbO3 films are deposited onto SiO2-buffered CMOS grade low resistivity (p = 10-20 cm) and high resistivity (p = 15-45 kcm) silicon substrates. Planar capacitors with 2 or 4 m gaps between electrodes have been fabricated on top of ferroelectric films. These devices have been characterized in the frequency range 1.0 MHz to 50 GHz at temperatures 30 - 300K. Na0.5K0.5NbO3/SiO2/Si structures on high resistivity silicon substrate exhibit C-V performances typical for Metal-Insulator- Semiconductor (MIS) capacitors. At low frequencies, f 1.0 GHz, the large tuneability and large losses are associated with the MIS structure, while at higher microwave frequencies the tuneability is mainly associated with the ferroelectric, film. At 1.0 MHz and room temperature, the tuneability of Na0.5K0.5NbO3/SiO2/Si structures more than 90%, reducing to 10-15 % at 50 GHz. The losses decrease with increasing the DC bias and frequency. A Q-factor more than 15 at 50 GHz is observed. The dielectric permittivity of the Na0.5K0.5NbO3 film is in the range 50-150 at frequencies 0.045-50 GHz. On low resistivity substrate the performance of Na0.5K0.5NbO3 films is completely screened by the high losses in silicon, and the tuneability is negligible

  • 3.
    Abiri, Olufunminiyi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Non-local models in manufacturing simulations2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ductile fracture presents challenges with respect to material modelling andnumerical simulations of localization. The strain and damage localization maybe unwanted as it indicates a failure in the process or, as in the case ofmachining and cutting, a wanted phenomenon to be controlled. The latterrequires a higher accuracy regarding the modelling of the underlying coupledplastic and fracturing/damage behaviour of the material, metal in the currentcontext as well as the stability and robustness of the simulation procedure.This aim of this work is to develop, evaluate and implement formulations thatcan efficiently and reliably handle localization problems in machiningsimulations. The focus is on non-local models. The non-local models extendthe standard continuum mechanics theory by using non-local continuumtheory in order to achieve mesh independent results when simulating fractureor shear localization.The non-local damage model is implemented and various formulations areevaluated in a Matlab™ based finite element code. The chosen algorithm wasthen implemented in commercial software. The implementations remedy themesh sensitivity problem and gives convergent solution for metal cuttingsimulations with reasonable cost. The length scale associated with the nonlocalmodels are in the current context considered as a numericalregularization parameter. The model has been applied in machiningsimulations and compared with measurements from industry.Keywords: Finite element simulation; Non-local damage; Plasticity; Machining

  • 4.
    Abiri, Olufunminiyi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simplifications of non-local damage models2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ductile fracture presents challenges with respect to material modelling and numerical simulations of localization. The strain and damage localization may be unwanted as it indicates a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying coupled plastic and fracturing/damage behaviour of the material, metal in the current context as well as the robustness of the simulation procedure. The focus of this thesis is on efficient and reliable finite element solution of the localization problem through the non-local damage model. The non-local damage model extends the standard continuum mechanics theory by using non-local continuum theory in order to achieve mesh independent results when simulating fracture or shear localization. In this work, the non-local damage model and its various simplifications are evaluated in an in-house finite element code developed using Matlab™. The accuracy, robustness, efficiency and costs of the models are investigated and also compared to a general multi-length scale finite element formulation. A numerical study versus published data is used to demonstrate the validity of the model. The explicit non-local damage variant will be implemented in a commercial finite element code for use in machining simulation

  • 5.
    Abiri, Olufunminiyi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Non-local damage models in manufacturing simulations2013Conference paper (Refereed)
    Abstract [en]

    Localisation of deformation is a problem in several manufacturing processes. Machining is an exception where it is a wanted feature. However, it is always a problem in finite element modelling of these processes due to mesh sensitivity of the computed results. The remedy is to incorporate a length scale into the numerical formulations in order to achieve convergent solutions. Different simplifications in the implementation of a non-local damage model are evaluated with respect to temporal and spatial discretisation to show the effect of different approximations on accuracy and convergence.

  • 6.
    Abiri, Olufunminiyi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Non-local damage models in manufacturing simulations2015In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 49, 548-560 p.Article in journal (Refereed)
    Abstract [en]

    Localisation of deformation is a problem in several manufacturing processes. Machining is an exception where it is a wanted feature. However, it is always a problem in finite element modelling of these processes due to mesh sensitivity of the computed results. The remedy is to incorporate a length scale into the numerical formulations in order to achieve convergent solutions. Different simplifications in the implementation of a non-local damage model are evaluated with respect to temporal and spatial discretisation to show the effect of different approximations on accuracy and convergence.

  • 7.
    Abiri, Olufunminiyi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Qin, Hao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Comparison of Multiresolution Continuum Theory and Nonlocal Dame model for use in Simulation of Manufacutring Processes2016In: International Journal for Multiscale Computational Engineering, ISSN 1543-1649, Vol. 14, no 1, 81-94 p.Article in journal (Refereed)
    Abstract [en]

    Modelling and simulation of manufacturing processes may require the capability to account for localization behavior, often associated with damage/fracture. It may be unwanted localization indicating a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying physics, as well as the robustness of the simulation procedure. Two different approaches for achieving mesh-independent solutions are compared in this paper. They are the multiresolution continuum theory (MRCT) and nonlocal damage model. The MRCT theory is a general multilength-scale finite element formulation, while the nonlocal damage model is a specialized method using a weighted averaging of softening internal variables over a spatial neighborhood of the material point. Both approaches result in a converged finite element solution of the localization problem upon mesh refinement. This study compares the accuracy and robustness of their numerical schemes in implicit finite element codes for the plane strain shear deformation test case. Final remarks concerning ease of implementation of the methods in commercial finite element packages are also given.

  • 8.
    Abiri, Olufunminiyi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. University of Johannesburg, South Africa.
    Svoboda, Ales
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Wedberg, Dan
    Controlling Thermal Softening Using Non-Local Temperature Field in Modelling2016In: Journal of Machining and Forming Technologies, ISSN 1947-4369, Vol. 8, no 1-2, 13-28 p.Article in journal (Refereed)
    Abstract [en]

    One of the aims of this work is to show that thermal softening due to the reduced flow strength of a material with increasing temperature may cause chip serrations to form during machining. The other purpose, the main focus of the paper, is to demonstrate that a non-local temperature field can be used to control these serrations. The non-local temperature is a weighted average of the temperature field in the region surrounding an integration point. Its size is determined by a length scale. This length scale may be based on the physics of the process but is taken here as a regularization parameter.

  • 9.
    Abiri, Olufunminiyi
    et al.
    Institute of Intelligent Systems, University of Johannesburg.
    Wedberg, Dan
    AB Sandvik Coromant.
    Svoboda, Ales
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Non-Local Modelling of Strain Softening in Machining Simulations2017In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 225, 012053Article in journal (Refereed)
    Abstract [en]

    Non-local damage model for strain softening in a machining simulation is presented in this paper. The coupled damage-plasticity model consists of a physically based dislocation density model and a damage model driven by plastic straining in combination with the stress state. The predicted chip serration is highly consistent with the measurement results. 

  • 10.
    Akhtar, Farid
    Institute of Powder Metallurgy, University of Science & Technology, Beijing.
    A new method to process high strength TiCN stainless steel matrix composites2007In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, no 3, 250-254 p.Article in journal (Refereed)
    Abstract [en]

    Layered composites of Ti(C, N) reinforcements and stainless steel have been prepared successfully by powder technology. The layer composite consisted of two layers. The upper layer consisted of TiCN reinforcements and stainless steel as binder material. The lower layer was entirely of binder material (stainless steel). The micro structural study revealed that the upper layer (TiCN/465 stainless steel) showed core–rim microstructure of conventional cermets and the lower layer showed the structure of sintered steel. An intermediate layer was formed due to diffusion reaction of upper and lower layers. This intermediate layer showed a gradient microstructure. The bending strength of the layered material measured was remarkably higher. Ninety per cent increase in the bending strength in the case of 50 wt-% reinforcement in the upper layer was found. The fracture morphologies of upper, lower and intermediate layers are also reported

  • 11.
    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, 145-151 p.Article 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.

  • 12.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Carbide reinforced steel matrix composites2009In: Recent Research Developments in Materials Science, Research Signpost, 2009Chapter in book (Refereed)
  • 13.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ceramic reinforced high modulus steel composites: processing, microstructure and properties2014In: Canadian metallurgical quarterly, ISSN 0008-4433, E-ISSN 1879-1395, Vol. 53, no 3, 253-263 p.Article in journal (Refereed)
    Abstract [en]

    Ceramic reinforced steel matrix composites are materials for automotive, aerospace, wear and cutting applications. Such metal matrix composites (MMCs) combine attractive physical, mechanical and wear properties with ease of fabrication and low cost. The review focuses on the current state of the art of producing these metal matrix composites, ceramics reinforcements, composition of steel matrix, microstructure evolution and parameters influencing the mechanical and wear properties. Processing methods to fabricate ceramic reinforced steel matrix composites are discussed to produce these composites with low number of defects, homogeneous microstructure and high mechanical and wear performance. The influence of chemical nature of ceramic reinforcements and composition of steel matrix on the microstructure, mechanical and wear properties is presented. The strengthening mechanisms and parameters controlling wear performance of steel MMCs are described as a function of the content of ceramic reinforcements, microstructural design and structure of the steel matrix. Keeping in view the stability of ceramics in steels, suitable ceramic reinforcements and steel matrix materials are discussed. Moreover, the importance of microstructure and interface between ceramic reinforcement and steel matrix in controlling the mechanical properties of steel MMCs is highlighted. The review identifies area of research for development to fully appreciate and tailor the properties of these industrially important composites.

  • 14.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Effect of additive Cu-10Sn alloy on sintering Behavior of elemental powders in composition of 465 stainless steel2007In: Journal of Iron and Steel Research International, ISSN 1006-706X, E-ISSN 2210-3988, Vol. 14, no 4, 61-74 p.Article in journal (Refereed)
    Abstract [en]

    The addition of Cu-10Sn alloy for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated include the sintering temperature, the sintering time, and the mass percent of Cu-10Sn. For vacuum sintering, effective sintering occurs at temperature between 1250°C and 1300°C. The maximum sintered density was achieved at 1300°C for 60 min with 3% (in mass percent) Cu-10Sn alloy. More than 3% (in mass percent) Cu-10Sn content and temperature above 1300°C caused slumping of the samples. A maximum density of 7.4 g/cm3 was achieved with 3% (in mass percent) Cu-10Sn content at a sintering temperature of 1300°C for 60 min. A maximum ultimate tensile strength (UTS) of 517 MPa was achieved with 3% (in mass percent) Cu-10Sn content. With content higher than 2% (in mass percent) Cu-10Sn, a maximum increase in the density was observed. The fracture morphologies of the sintered samples are also reported.

  • 15.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Effect of Microstructural Parameters on the Wear Properties of High Volume Ceramic Reinforced Metal Matrix Composites2009In: Powder Metallurgy Research Trends, New York: Nova Science Publishers, Incorporated , 2009Chapter in book (Refereed)
  • 16.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hierarchical zeolites for carbon capture2014Patent (Other (popular science, discussion, etc.))
  • 17.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    High volume fraction carbide reinforced copper matrix composites for sliding contact applications2007In: PRICM 6: selected, peer reviewed papers from the Sixth Pacific Rim International Conference on Advanced Materials and Processing, November 5 - 9, 2007, ICC Jeju, Jeju Island, Korea / [ed] Young Won Chang; Nack J. Kim; Chong Soo Lee, Stafa-Zurich: Trans Tech Publications Inc., 2007, 627-630 p.Conference paper (Refereed)
    Abstract [en]

    This study deals with the processing, microstructure and properties of the carbide reinforced copper matrix composites. Powder technology was used to successfully fabricate the composites. NbC particulates were used as reinforcements for copper matrix. The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the NbC particles were distributed uniformly in the matrix phase. No interface debonding and micro- cracks were observed in the composite. NbC particles were found in round shape in copper matrix composite. The composite hardness of 78 HRA was found with 60vol% NbC content. Electrical conductivity as high as 7%IACS was achieved. The wear performance and conductivity value predicts that NbC reinforced copper matrix composites can be used as sliding contact applications.

  • 18.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Microstructure evolution and wear properties of in situ synthesized TiB 2 and TiC reinforced steel matrix composites2008In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 459, no 1-2, 491-497 p.Article in journal (Refereed)
    Abstract [en]

    Steel matrix composite reinforced with TiB2 and TiC reinforcements (30 to 70wt%) have been produced through the synthesis reaction from Ti, C and FeB. The sintered composites were characterized by X-ray diffraction and scanning electron microscopy. TiB2, TiC and steel were detected by X-ray diffraction analysis. The scanning electron micrographs revealed the morphology and distribution of the reinforcements. TiB2 and TiC were thermally stable in the steel matrix. The results showed that different mechanisms of evolution of reinforcements in steel matrix were operative. TiB2 grew in hexagonal prismatic or rectangular shape and TiC in spherical shape. The reciprocating sliding wear test was conducted on the composite. The results of sliding wear showed that the wear loss decreased with increase in the reinforcement content. The wear mechanisms were polishing wear and microploughing for the composites containing high volume fraction of the reinforcements, whereas microploughing and grooving were the dominant wear mechanisms for the composites containing low volume fraction of the reinforcements.

  • 19.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    On the microstructure and properties of tungsten heavy alloys2007In: Advanced materials and processing: selected, peer reviewed papers from the Sixth Pacific Rim International Conference on Advanced Materials and Processing, November 5-9, 2007, ICC Jeju, Jeju Island, Korea, PRICM 6 / [ed] Young Won Chang; Nack J. Kim; Chong Soo Lee, Stafa-Zurich: Trans Tech Publications Inc., 2007, Vol. 26-28, 1055-1058 p.Conference paper (Refereed)
    Abstract [en]

    In this research, the effect of microstructure on the mechanical properties of tungsten heavy alloys is discussed. The tensile properties of tungsten heavy alloys are found to be dependent on volume fraction of W, contiguity and grain size of W particle. The ductility is found to be influenced by contiguity and connectivity. The volume fraction of matrix increases sharply with the increase in rare metal oxide impurity, which adversely affects the mechanical properties of tungsten heavy alloys.

  • 20.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Processing, microstructure, properties and wear behavior of in situ synthesized TiB 2 and TiC thick films on steel substrates2007In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, no 24, 9603-9609 p.Article in journal (Refereed)
    Abstract [en]

    TiB2 and TiC reinforced Fe matrix thick films (2 mm thickness) were produced through the synthesis reaction from Ti, C and FeB powders with varying porosity on the steel substrates. Powder technology was used as a processing method. The films and the substrates were sintered in a single step. TiB2, TiC and Fe were detected in the films by X-ray diffraction analysis. The fact that no other reaction product was detected revealed the thermal stability of TiB2 and TiC. The formation of secondary reaction products was inhibited during the reactive sintering. The films showed maximum strength of 163–466 MPa when sintered separately at 1350 °C. The strength of the films varied with their porosity. The films showed considerable bonding strength with the steel substrates. The delamination of the films from the steel substrates was observed at stress values from 454–781 MPa. The microstructure, fracture and delaminated surface morphologies were studied. The wear resistance against hardened high speed steel was studied in reciprocating sliding tests. The wear mechanisms were discussed by means of microscopical observation on the worn surfaces

  • 21.
    Akhtar, Farid
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Pulse current processing of hierarchically porous monoliths from macro and microporous powders2009Conference paper (Other academic)
  • 22.
    Akhtar, Farid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Sintering behavior of elemental powders with FeB addition in the composition of martensitic stainless steel2007In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 16, no 6, 726-729 p.Article in journal (Refereed)
    Abstract [en]

    The effect of sintering additive for the development of high-strength martensitic stainless steel from elemental powders was studied. The sintering parameters investigated were: sintering temperature, sintering time, and wt.% of FeB. In vacuum sintering, effective sintering took place between 1300 and 1350 °C with 1-1.5 wt.% FeB addition. The maximum sintered density and ultimate tensile strength (UTS) were achieved after sintering at 1350°C for 60 min with 1 wt.% FeB. Secondary pores were observed in samples containing more than 1.5 wt.% FeB sintered at 1350 °C for 60 min. More than 1.5 wt.% FeB content and temperature above 1350°C caused slumping of the specimens. Maximum UTS of 505 MPa was achieved with 1 wt.% FeB content. Above 0.5 wt.% FeB content, maximum increase in density was observed. Fracture morphologies of the sintered samples are reported.

  • 23.
    Akhtar, Farid
    Stockholm University.
    Stainless Steel Polymer Composites2012In: Wiley Encyclopedia of Composites, John Wiley & Sons, 2012Chapter in book (Refereed)
    Abstract [en]

    In electronic, automotive, medical, and aerospace industries, electrostatic discharge (ESD) control and electromagnetic interference (EMI) shielding are important design considerations. Conductive polymer composites are well researched and commercially available materials for ESD control and EMI shielding. Several kinds of conductive fillers are incorporated in the form of particulates and fibers in polymer matrix. A comparison between various conductive fillers in polymer matrix is presented. Stainless steel fibers as conductive filler for polymer matrix offer several advantages. Polymer composites show resistivities in the range of 103−106 Ω/sq at a volume fraction as low as 0.75 vol% of stainless steel fibers. The effect of filler size, shape of the filler, critical volume fraction, and effect of polymer matrix on the ESD control/EMI shielding properties of the stainless steel-reinforced conductive polymer composite is discussed. Important parameters are described to obtain effective ESD control and EMI shielding using stainless fiber polymer matrix composites. Several reported stainless steel-reinforced polymer composites are summarized and their effectiveness for ESD control and EMI shielding is compared

  • 24.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Stockholm University.
    Structured adsorbents with High CO2 over N2 selectivity and CO2 uptake capacity2012In: 2012 AIChE annual meeting: David L. Lawrence Convention Center, Pittsburgh, PA, October 28-November 2, 2012 : conference proceedings., New York: American Institute of Chemical Engineers, 2012Conference paper (Refereed)
    Abstract [en]

    Structured adsorbents with high CO2 adsorption capacity, CO2 over N2 selectivity and rapid adsorption and desorption kinetics are ideal for CO2 capture from power-plant flue gas at a low cost. We report here binder-free zeolite monoliths with high CO2 over N2 selectivity (> 500) and uptake capacity (4mmolg-1) at 298 K and 101 kPa. Binder-free zeolite monoliths were consolidated by a rapid and facile processing approach called pulse current processing (PCP) from partially K exchanged NaA powders. The pore widow size of NaA was optimized by partially exchanging Na with K cations to achieve a high CO2 over N2 selectivity while maintaining a high CO2 uptake capacity. The CO2 uptake from binary mixtures of 0.10CO2-0.90N2 was obtained from the single component CO2 and N2 adsorption isotherms by applying Ideal adsorption solution (IAS) and Fast IAS theories. The binder-free adsorbents with an optimum degree of ion exchange display extraordinarily high CO2 over N2 selectivity and high CO2 uptake, together with a rapid CO2 adsorption and desorption kinetics and high mechanical stability. The performance of the new adsorbent has been compared with other potential candidates for efficient swing adsorption processes by a figure of merit. Key words: CO2 Capture; Zeolite monoliths; Pulse current processing; Selectivity; Adsorption; Ideal adsorbed solution (IAS) theory

  • 25.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring gas adsorbents by processing of porous powders2014Conference paper (Refereed)
  • 26.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring of Aluminophosphates Monoliths for Carbon Capture2015Conference paper (Refereed)
  • 27.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring of Nanoporous Powders into Hierarchically Porous Nanostructured Adsorbents for Clean Energy2016Conference paper (Refereed)
  • 28.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring of nanoporous powders into hierarchically porous nanostructured adsorbents for decarbunization2015Conference paper (Refereed)
  • 29.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Structuring of porous powders for gas separation applications2013Conference paper (Other academic)
  • 30.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Structuring of porous powders into hierarchically porous adsorbents2013Conference paper (Refereed)
  • 31.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Synthesis, microstructure and mechanical properties of Al 2 O 3 reinforced Ni 3 Al matrix composite2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 499, no 1-2, 415-420 p.Article in journal (Refereed)
    Abstract [en]

    A new method to synthesize alumina reinforced Ni3Al intermetallic matrix composites has been described. The powder mixture of nickel and aluminium was mechanically alloyed. The powder mixture was excessively heated during mechanical alloying and then exposed to atmosphere for oxidation. The oxidized powder mixture was transformed into alumina reinforced nickel aluminide matrix composite on subsequent pulse current processing. Alumina reinforcements were generated in the nickel aluminide matrix by in situ precipitation. The microstructure of the composite showed that the alumina reinforcements were 50–150 nm in size. The fine alumina reinforcements were homogeneously distributed in the matrix phase. The mechanical properties of the alumina reinforced nickel aluminide matrix composite fairly exceeded the nickel aluminide alloys. This novel synthesis approach allowed the rapid and facile production of high strength alumina reinforced Ni3Al matrix composites.

  • 32.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Zeolite adsorbents for gas separation applications2013Conference paper (Refereed)
  • 33.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ali, Liaqat
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Peizhong, Feng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Shah, Jawad Ali
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Enhanced sintering, microstructure evolution and mechanical properties of 316l stainless steel with MoSi 2 addition2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, no 35, 8794-8797 p.Article in journal (Refereed)
    Abstract [en]

    Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi2 ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi2 as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi2 content. The distribution of MoSi2 was characterized by XMAPs. It was found that MoSi2 dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 °C for 60 min with 5 wt.% MoSi2 content. The stainless steel sintered with 5 wt.% MoSi2 exhibited very attractive mechanical properties.

  • 34.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Andersson, Linnéa
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Colloidal processing and CO 2 capture performance of sacrificially templated zeolite monoliths2012In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 97, 289-296 p.Article in journal (Refereed)
    Abstract [en]

    Sacrificial templating of suspension cast and subsequently thermally treated zeolite monoliths with glassy carbon spheres and fibers yielded zeolite 13X and silicalite-1 monoliths with macroporosities up to 50 vol%. Homogeneous distribution of the macroporosity in hierarchically porous monoliths was obtained by tailoring the surface chemistry of the carbon particles by polyelectrolyte-assisted adsorption of zeolite particles. The effect of amount of kaolin binder and temperature for the thermal treatment on the monoliths strength, surface area and CO2 uptake was studied by diametral compression tests, electron microscopy, X-ray diffraction and gas adsorption. Cyclic adsorption and regeneration measurements showed that zeolite 13X monoliths display a high CO2 uptake while the silicalite-1 monoliths could be regenerated with a relatively low energy penalty.

  • 35.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Andersson, Linnéa
    School of Chemical, Biological and Environmental Engineering, Oregon State University.
    Ogunwumi, Steven
    Crystalline Materials Research, Corning Incorporated.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Structuring adsorbents and catalysts by processing of porous powders2014In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 34, no 7, 1643-1666 p.Article in journal (Refereed)
    Abstract [en]

    Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.

  • 36.
    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, 327-336 p.Article 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.

  • 37.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Askari, Syed Jawid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shaft, Jawad Ali
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Processing, microstructure and mechanical properties of TiC-465 stainless steel/465 stainless steel layer composites2007In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 439, no 1-2, 287-293 p.Article in journal (Refereed)
    Abstract [en]

    Layered composites of carbide reinforcements and stainless steel have been prepared successfully by powder technology. The layer material consisted of two layers. Top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as binder material for carbides. The substrate material was of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that top layer (TiC-NbC/465 stainless steel) showed the typical core-rim microstructure of conventional steel bonded cermets and the substrate material showed the structure of sintered steel. An intermediate layer was formed due to diffusion reaction of top layer and substrate material. This intermediate layer showed a gradient microstructure. The bending strength of layered material measured in the direction perpendicular to the layer alignment was remarkably higher. Nineteen percent increase in bending strength in case of 53 wt% reinforcement in top layer and 35% increase in case of 73 wt% reinforcement in top layer was found. The variation of strength as a function of thickness of substrate material revealed that the character of material changed from cermet to a layer composite and then towards metallic materials. The fracture morphologies of top layer, substrate material and intermediate layer are also reported

  • 38.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Colloidal processing and thermal treatment of binderless hierarchically porous zeolite 13X monoliths for CO2 capture2011In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, no 1, 199-205 p.Article in journal (Refereed)
    Abstract [en]

    Adsorbents with high surface area are potential candidates for efficient postcombustion CO2 capture. Binderless zeolite 13X monoliths with a hierarchical porosity and high CO2 uptake have been produced by slip casting followed by pressureless thermal treatment. The zeolite powder displayed an isoelectric point at pH 4.7 and electrostatically stabilized suspensions could be prepared at alkaline pH. The volume fraction-dependent steady shear viscosity could be fitted to a modified Krieger–Dougherty model with a maximum volume fraction of 0.66. The narrow temperature range where monoliths could be produced without significant loss of the microporous surface area was identified and related to the phase behavior of the 13X material. Slip casting of concentrated suspensions followed by thermal treatment of the powder bodies at a temperature of 800°C without holding time resulted into strong hierarchically porous zeolite 13X monolith that displayed a CO2 uptake larger than 29 wt%.

  • 39.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ogunwumi, Steven
    Laminates for rapid CO2 capture from gas mixtures2013Patent (Other (popular science, discussion, etc.))
  • 40.
    Akhtar, Farid
    et al.
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Du, Xueli
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Jawid, Askari Syed
    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.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Microstructure and property evolution during the sintering of stainless steel alloy with Si 3 N 42008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 472, no 1-2, 324-331 p.Article in journal (Refereed)
    Abstract [en]

    This paper describes the sintering of a martensitic stainless steel alloy with addition of Si3N4. Sintering behavior was studied at different sintering temperatures ranging from 1250 to 1400 °C with different holding times (20–80 min) and with varying Si3N4. Results showed that the samples were densified rapidly via liquid phase sintering mechanism. Nearly full density was obtained at 1300 °C after 60 min of holding time with 5 wt% Si3N4. Temperature above 1350 °C and Si3N4 content 10 wt% caused slumping of the samples. Two weight percent Si3N4 was found chemically stable in steel alloy. Above 2 wt% Si3N4 dissolved in the steel matrix. The distribution of dissolved Si and N was characterized by XMAP. When N content reached much above its solubility limit in steel alloy it diffused out leaving pores in steel alloy with considerable decrease in the sintered density. The mechanical properties of the sintered product with varying Si3N4 were measured. A maximum ultimate tensile strength of 1011 MPa was achieved with 2 wt% Si3N4 sintered at 1300 °C after 60 min of holding time. Fracture morphologies of tensile samples are also reported.

  • 41.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shi Ju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shah, Jawad Ali
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Feng, Pei Zhong
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Effect of adding a type of binder phase on the microstructure, properties and heat treatment of steel bonded TiC cermets2007In: Progress in powder metallurgy: proceedings of the 2006 Powder Metallurgy World Congress & Exhibition (PM 2006), held in Busan Exhibition & Convention Center (BEXCO), Busan, Korea, September 24 - 28, 2006 / [ed] Duk Yong Yoon; Suk-Joong L. Kang; Kwang Yong Eun; Yong-Seog Kim, Uetikon-Zürich: Trans Tech Publications Inc., 2007, Vol. 534-536, 1161-1164 p.Conference paper (Refereed)
    Abstract [en]

    Particulate TiC reinforced 465 maraging stainless steel matrix Cermets were processed by conventional P/M. The binder phase was added in the form of elemental powders and master alloy powders. The microstructures, binder phase variation with TiC content and mechanical properties were evaluated. The addition of a type of binder phase largely effects the microstructure and mechanical properties. When a master alloy binder phase was used the microstructure showed interphase debondings, microcracks and large growths of TiC particles. Where as, elemental powders in the composition of binder phases showed defect free microstructure of steel bonded cermets. The binder phase variation from starting composition was observed with increase in wt% TiC content and this variation was higher when the master alloy powders were used as a binder. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The response to heat treatment was decreased with an increase in TiC content due to the shift of binder phase from the starting composition.

  • 42.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, University of Science & Technology, Beijing.
    Guo, Shi-ju
    Institute of Powder Metallurgy, University of Science & Technology, Beijing.
    Development of Si 3 N 4/Al composite by pressureless melt infiltration2006In: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 16, no 3, 629-632 p.Article in journal (Refereed)
    Abstract [en]

    Pressureless infiltration processs to synthesize Si3N4/Al composite was investigated. Al-2%Mg alloy was infiltrated into Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al-2% Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with aluminium to form Si and AlN, the growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. Firstly, preform without Al2O3 content gives rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Secondly, perform with 10% Al2O3 content gives rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.

  • 43.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Development of Si3N4/ Al composite by pressureless melt infiltration2006In: European PM 2005 conference proceedings: Prague Congress Centre, Czech Republic, 2-5 October 2005., Shrewsbury: European powder metallurgy association , 2006, Vol. 2, 271-278 p.Conference paper (Refereed)
    Abstract [en]

    Pressureless infiltration process to synthesize Si3N4/ Al composite was investigated. Al- 2%Mg alloy was infiltrated into the Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al- 2%Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with Aluminium to form Si and AlN. The growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. First, preform without Al2O3 content gave rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Second, perform with 10% Al2O3 content gave rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.

  • 44.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    On the processing, microstructure, mechanical and wear properties of cermet/stainless steel layer composites2007In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, no 4, 1467-1477 p.Article in journal (Refereed)
    Abstract [en]

    This study deals with layer composites of carbide reinforcements and stainless steel prepared successfully by powder technology. The layer material consisted of two layers. The top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as the binder material for the carbides. The bottom layer was entirely of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the top layer (TiC–NbC/465 stainless steel) showed the typical core–rim microstructure of conventional steel bonded cermets and the bottom layer showed the structure of sintered steel. An intermediate layer was found with a gradient microstructure, having a higher carbide content towards the cermet layer and lower carbide content towards the stainless steel layer. The bending strength of the layered material measured in the direction perpendicular to the layer alignment was remarkably high. The variation of strength as a function of the thickness of the bottom layer revealed that the character of the material changed from the cermet, to a layer composite and then towards metallic materials. The wear resistance of the top layer was studied against high speed steel. The wear mechanisms were discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microploughing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microploughing and rapid removal of material from the wear surface was observed at high wear load. The fracture morphologies of the top, bottom and intermediate layers are reported

  • 45.
    Akhtar, Farid
    et al.
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Guo, Shi-Ju
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Pressureless infiltration of Si3N4 preforms with an Al-2wt% Mg alloy2005In: International Journal of Minerals, Metallurgy and Materials, ISSN 1674-4799, E-ISSN 1869-103X, Vol. 12, no 4, 351-356 p.Article in journal (Refereed)
    Abstract [en]

    The pressureless infiltration process to synthesize a silicon nitride composite was investigated. An Al-2wt%Mg alloy was infiltrated into silicon nitride preforms in the atmosphere of nitrogen. It is possible to infiltrate the Al-2wt%Mg alloy in silicon nitride preforms. The growth of the composite with useful thickness wasfacilitated by the presence of magnesium powder at the interface and by flowing nitrogen. The microstructure of the Si3N4-Al composite has been characterized using scanning electron microscope.During the infiltration of Si3N4 preforms, Si3N4 reacted with aluminium to form silicon and AlN. Thesilicon produced during the growth consumed in the formation of MgSiAlO, MgSiAlN and Al3.27Si0.47 type phases. The growth of the composite was found to proceed in two ways, depending on the oxide content in the initial preforms. First, less oxide content preforms gave rise to MgAlSiO and MgAlSiN type phases after infiltration. Second, more oxide content preforms gave rise to AlN-Al2O3 solid solution phase(AlON). The AlON phase was only present in the composite, containing 10% aluminium in the silicon nitride preforms before infiltration.

  • 46.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Askari, Jawid
    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.
    Sintering behavior, microstructure and properties of TiC-FeCr hard alloy2007In: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, Vol. 14, no 1, 89-93 p.Article in journal (Refereed)
    Abstract [en]

    TiC based cermets were produced with FeCr, as a binder, by conventional P/M (powder metallurgy) to near >97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of >1360°C caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360°C for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettability of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals

  • 47.
    Akhtar, Farid
    et al.
    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.
    Cui, Feng-e
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Feng, Peizhong
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Lin, Tao
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    TiB 2 and TiC stainless steel matrix composites2007In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 61, no 1, 189-191 p.Article in journal (Refereed)
    Abstract [en]

    Stainless steel matrix composites reinforced with TiB2 or TiC particulates have been in situ produced through the reactive sintering of Ti, C and FeB. X-ray diffraction analysis confirmed the completion of reaction. The TiB2, TiC and steel were detected by X-ray diffraction analysis. No other reaction product or boride was found, indicating the stability of TiB2 and TiC in steel matrix. The SEM micrographs revealed the morphology and distribution of in situ synthesized TiB2 and TiC reinforcements in steel matrix. During sintering the reinforcements TiB2 and TiC grew in different shapes. TiB2 grew in hexagonal prismatic and rectangular shape and TiC in spherical shape.

  • 48.
    Akhtar, Farid
    et al.
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Guo, Shiju
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Feng, Peizhong
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Ali, Shah Khadijah
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Javid, Askari Syed
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    TiC-maraging stainless steel composite: microstructure, mechanical and wear properties2006In: Xiyou jinshu, ISSN 1001-0521, E-ISSN 1867-7185, Vol. 25, no 6, 630-635 p.Article in journal (Refereed)
    Abstract [en]

    Particulate TiC reinforced 17-4PH and 465 maraging stainless steel matrix composites were processed by conventional powder metallurgy (P/M). TiC-maraging stainless steel composites with theoretical density >97% were produced using conventional P/M. The microstructure, and mechanical and wear properties of the composites were evaluated. The microstructure of the composites consisted of (core-rim structure) spherical and semi-spherical TiC particles depending on the wettability of the matrix with TiC particles. In TiC-maraging stainless steel composites, 465 stainless steel binder phase showed good wettability with TiC particles. Some microcracks appeared in the composites, indicating the presence of tensile stresses in the composites produced during sintering. The typical properties, hardness, and bend strength were reported for the composites. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The specific wear behavior of the composites strongly depends on the content of TiC particles and their interparticle spacing, and on the heat treatment of the maraging stainless steel.

  • 49.
    Akhtar, Farid
    et al.
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Guo, Shiju
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Yang, Xia
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Lian, Yudong
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Stainless steel binder for the development of novel TiC-reinforced steel cermets2006In: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, Vol. 13, no 6, 546-550 p.Article in journal (Refereed)
    Abstract [en]

    Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC-reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy (P/M). TiC-reinforced maraging stainless steel composites with >97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.

  • 50.
    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, 84-90 p.Article 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

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