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    Sintering of biocompatible P/M Co-Cr-Mo alloy (F-75) for fabrication of porosity-graded composite structures

    , Article Materials Science and Engineering A ; Volume 472, Issue 1-2 , 2008 , Pages 338-346 ; 09215093 (ISSN) Dourandish, M ; Godlinski, D ; Simchi, A ; Firouzdor, V ; Sharif University of Technology
    Manufacturing of complex-shaped bimetals utilizing two-color powder injection molding (2C-PIM) and three-dimensional printing (3DP) processes, which basically involve sintering of a powder/binder mixture, has been attracted a great interest. This article addresses sintering of biocompatible Co-Cr-Mo alloy for manufacturing stepwise porosity-graded composite structures. Such composite structures provide strength at the core and a porous layer for the tissue growth. To evaluate the process, two grades of gas atomized Co-Cr-Mo powder with an average particle size of 19 and 63 μm were used. Isothermal and non-isothermal sintering behavior of the loose powders under hydrogen and argon... 

    Interface formation and bond strength in 3Y-TZP/Cr composite bilayers produced by sinter–joining [electronic resource]

    , Article Materials Science and Engineering: A ; Volume 527, Issue 3, 15 January 2010, Pages 449–453 Dourandish, M ; Simchi, A. (Abdolreza) ; Hokamoto, K ; Tanaka, S ; Sharif University of Technology
    The mechanism of interface formation during sinter–joining of nanostructured yttria stabilized zirconia (27 nm) compacts with chromium powder was investigated. The effect of sintering atmosphere, i.e. argon or vacuum, was studied. Microstructural evaluation and phase formation was examined by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and micro-focused X-ray diffraction (MFXRD) methods. It is shown that spreading and evaporation–condensation mechanisms are responsible for the interface formation. An improved joint shear-strength was obtained after sintering in vacuum (74 MPa) compared with argon (41 MPa). The result of MFXRD indicated formation of Cr-island at... 

    Cold compaction behavior and pressureless sinterability of ball milled WC and WC/Cu powders

    , Article Science of Sintering ; Volume 48, Issue 1 , 2016 , Pages 71-79 ; 0350820X (ISSN) Hashemi, S. R ; Ardestani, M ; Nemati, A ; Sharif University of Technology
    International Institute for the Science of Sintering (IISS)  2016
    In this research, cold compaction behavior and pressureless sinterability of WC, WC-10%wtCu and WC-30%wtCu powders were investigated. WC and WC/Cu powders were milled in a planetary ball mill for 20h. The milled powders were cold compacted at 100, 200, 300 and 400 MPa pressures. The compressibility behavior of the powders was evaluated using the Heckel, Panelli-Ambrosio and Ge models. The results showed that the PanelliAmbrosio was the preferred equation for description the cold compaction behavior of the milled WC and WC-30%wtCu powders. Also, the most accurate model for describing the compressibility of WC-10%wtCu powders was the Heckel equation. The cold compacts were sintered at 1400oC.... 

    Optimization of process parameters for reducing warpage in selected laser sintering of polymer parts

    , Article Additive Manufacturing ; Volume 18 , 2017 , Pages 285-294 ; 22148604 (ISSN) Ahmadi Dastjerdi, A ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
    Selective Laser Sintering (SLS) is a rapidly growing additive manufacturing process, because it has the capacity to build parts from a variety of materials. However, the dimensional accuracy of the fabricated parts in this process is dependent on the ability to control phenomena such as warpage and shrinkage. This research presents an optimization algorithm to find the best processing parameters for minimizing warpage. The finite element method was used to simulate the sintering of a layer of polymer powder, and the warpage of the layer was calculated. The numerical model was verified through comparison with experimental results. A back-propagation neural network was used to formulate the... 

    Direct laser sintering of metal powders: Mechanism, kinetics and microstructural features

    , Article Materials Science and Engineering A ; Volume 428, Issue 1-2 , 2006 , Pages 148-158 ; 09215093 (ISSN) Simchi, A ; Sharif University of Technology
    In the present work, the densification and microstructural evolution during direct laser sintering of metal powders were studied. Various ferrous powders including Fe, Fe-C, Fe-Cu, Fe-C-Cu-P, 316L stainless steel, and M2 high-speed steel were used. The empirical sintering rate data was related to the energy input of the laser beam according to the first order kinetics equation to establish a simple sintering model. The equation calculates the densification of metal powders during direct laser sintering process as a function of operating parameters including laser power, scan rate, layer thickness and scan line spacing. It was found that when melting/solidification approach is the mechanism... 

    Effects of porosity on delamination wear behaviour of sintered plain iron

    , Article Powder Metallurgy ; Volume 47, Issue 1 , 2004 , Pages 73-80 ; 00325899 (ISSN) Simchi, A ; Danninger, H ; Sharif University of Technology
    IOM Communications Ltd  2004
    The role of porosity on the wear behaviour of sintered iron was investigated. Sintered iron was used in preference to steel because the various alloy additions and matrix heterogeneity in the latter might affect the microwear behaviour and the role of porosity. The wear tests were performed in a pin on disc test bed under 10-40 N loads at 0·56 m s-1 sliding speed in air. For the given tribological conditions, it was found that the wear mechanism is delamination or mechanical wear, which is basically similar to that of wrought materials according to subsurface crack generation and crack propagation processes. However, the open pores on the surface act as a site for generation and collection... 

    Effects of lubrication procedure on the consolidation, sintering and microstructural features of powder compacts

    , Article Materials and Design ; Volume 24, Issue 8 , 2003 , Pages 585-594 ; 02641275 (ISSN) Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2003
    The role of lubrication procedure on the consolidation behavior of metallic powders and subsequent microstructural development during sintering was investigated. Iron powder and iron-0.8 w/o graphite powder mixture were used as model materials. The effects of die wall lubrication procedure were compared to the traditional admixed powder lubrication method. The influences of manufacturing parameters such as the compacting pressure in the range of 150-800 MPa and the sintering temperature from 400 to 1300 °C were studied. It was found that the lubrication procedure has a great influence on the consolidation and microstructural features of the materials investigated. Admixed lubricant aids the... 

    Axial fatigue behavior of MoNiCu alloyed sintered steel

    , Article Proceedings of the 3rd International Powder Metallurgy Conference, Ankara, 4 September 2002 through 8 September 2002 ; 2002 , Pages 398-407 ; 9759246309 (ISBN) Habibi, S. M ; Janghorban, K ; Khorsand, H ; Yoozbashizade, H ; Jahromi, S. A. J ; Sharif University of Technology
    In recent years, PM steel parts have been used due to materials saving and cost. Mechanical properties of PM parts made of Ultrapac-LA (Fe-.5Mo-1.5Cu-1. 75Ni) with 0.2 and 0.5% graphite addition have been studied. The chemical composition of Ultrapac-LA is similar to Distaloy AB. Specimens with dimensions of 89×6×5.5 mm were prepared. The green compacts were sintered at 1120°C in a 75 H2 -25 N2 atmosphere for 40 minutes to densities in the range of 6.7g/cm3 to 7 g/cm3. They were tested in static and cyclic loading, and their microstructures were studied by optical microscopy. Results show that porosity has a definite effect on fatigue resistance of this alloy. The formation of bainite and... 

    Effect of C and Cu addition on the densification and microstructure of iron powder in direct laser sintering process

    , Article Materials Letters ; Volume 62, Issue 17-18 , 2008 , Pages 2840-2843 ; 0167577X (ISSN) Simchi, A ; Sharif University of Technology
    Laser sintering of Fe-C-Cu steel powder for rapid manufacturing of sintered components for functional testing was studied. The effects of C and Cu addition on the densification and the attendant microstructural features were investigated. The influence of iron particle size on the sintering kinetics was also examined. It is shown that the alloying elements significantly improve the densification rate when fine iron particles and high laser intensity are used. The mechanism of particle bonding and the effect of the alloying elements are presented. © 2008 Elsevier B.V. All rights reserved  

    Partially stabilization of Zirconia and its effects on the Magnesia - Spinel refractory properties

    , Article UNITECR '05 - Unified International Technical Conference on Refractories: 9th Biennial Worldwide Congress on Refractories, Orlando, FL, 8 November 2005 through 11 November 2005 ; 2006 , Pages 715-721 ; 1574982656 (ISBN) Kazemi, A ; Nemati, Z. A ; Faghihi Sani, M. A ; Zahed, F ; Sharif University of Technology
    In this research, Magnesia Spinel refractories were formulated by using sintered magnesia, Tabular and Calcined Alumina and sintered Spinel. The grain size distribution of raw materials was modified, using the Andreessen equation. In order to improve the physical and mechanical properties and corrosion resistance of specimens, none stabilized Zirconia was added to the system. The pressed samples were sintered at 1700°C and the properties were evaluated at room and high temperatures. The formed phases and resultant microstructure were also, analyzed by XRD and SEM. The corrosion test was conducted in two parts. First, the depth of corrosion was measured in two zone, within 0-1mm and 1-2 mm... 

    Ultra-high voltage SnO2 based varistors prepared at low temperature by two-step sintering

    , Article Journal of Alloys and Compounds ; Volume 805 , 2019 , Pages 794-801 ; 09258388 (ISSN) Maleki Shahraki, M ; Delshad Chermahini, M ; Alipour, S ; Mahmoudi, P ; Safaee, I ; Abdollahi, M ; Sharif University of Technology
    Elsevier Ltd  2019
    In this research, full density, single phase microstructure (in the XRD and SEM detection limits), and fine-grained SnO2 varistors with an average grain size of 0.65 μm was acquired at low temperature by the two-step sintering technique. The sintering temperature was successfully decreased from 1300 °C in the normal sintering to 1150 °C and 1100 °C of respectively the first and the second stage in the two-step sintering. The mechanism of grain growth suppression of the two-step sintered samples was discussed and it was suggested that in addition to triple point junction, solute drag and/or nano-secondary phases contribute to cease the grain growth. These SnO2 varistors exhibited ultra-high... 

    Effect of sintering atmosphere and carbon content on the densification and microstructure of laser-sintered M2 high-speed steel powder

    , Article Materials Science and Engineering A ; Volume 403, Issue 1-2 , 2005 , Pages 290-298 ; 09215093 (ISSN) Asgharzadeh, H ; Simchi, A ; Sharif University of Technology
    In the present work, the role of graphite addition and sintering atmosphere on the laser sintering of M2 high-speed steel (HSS) powder was studied. The test specimens were produced using a continuous wave CO2 laser beam at power of 200 W and at varying scan rate ranges from 50 to 175 mm s-1 under nitrogen and argon atmospheres. It was found that laser scan rate and sintering atmosphere strongly influence the densification of M2 HSS powder. Opposite to the conventional sintering that the sinterability of HSS is improved by graphite addition, the result of this work demonstrated that graphite addition decreases the sintered density of M2 HSS at relatively low laser scan rates, i.e. <100 mm... 

    Adjustment of materials and sintering processes for MIM of Bi-material parts

    , Article European Powder Metallurgy Congress and Exhibition, Euro PM 2005, Prague, 2 October 2005 through 5 October 2005 ; Volume 2 , 2005 , Pages 315-320 ; 9781899072187 (ISBN) Imgrund, P ; Rota, A ; Hartwig, T ; Petzoldt, F ; Simchi, A ; European Powder Metallurgy Association ; Sharif University of Technology
    European Powder Metallurgy Association (EPMA)  2005
    In this paper, an investigation of bi-material parts produced by a two-component metal injection moulding process is presented. The compatibility of different materials for this process was evaluated by sinter dilatometry, taking into account the effects of powder particle size, powder loading and use of master alloys on the sintering behaviour. In a second step, sample material joints of 316L / H13, 316L / 17-4PH and 316L / iron were moulded, debinded and sintered together. The interfaces obtained were examined by optical microscopy and SEM. The diffusion of alloying elements across the interfaces was shown as a function of sintering temperatures. Changes in microstructures and chemical... 

    Phase formation during sintering of nanocrystalline zirconia/stainless steel functionally graded composite layers [electronic resource]

    , Article Journal of Materials Letters ; 15 February 2011, Volume 65, Issue 3, Pages 523–526 Dourandish, M ; Simchi, A. (Abdolreza) ; Hokamoto, K ; Tanaka, S ; Sharif University of Technology
    Microstructural development and phase formation at the interface of yttria stabilized zirconia (3Y-TZP)/430L stainless steel composite layers produced by co-sintering method were studied by SEM, HRTEM, micro-focus XRD, and EPMA. Formation of a rich chromium boundary layer at the interface was noticed, which revealed Cr aggregation at the interface at the elevated temperatures. Misfit dislocations were also observed at the joint interface to tackle the mismatch crystallographic orientations between the ceramic and metal layer. The results of the micro-focus XRD showed formation of no new phases at the boundary zone. Microstructural studies also revealed a retarded grain growth in the... 

    Sintering viscosity and sintering stress of nanostructured WC–Co parts prepared by powder injection moulding [electronic resource]

    , Article Journal of Powder Metallurgy ; Februrary 2011, Volume 54, Issue 1, P. 84-88 Simchi, A. (Abdolreza) ; Sharif University of Technology
    The uniaxial viscosity and sintering stress of WC-10Co-0⊙ 9VC (wt-%) were obtained by a loading dilatometer as functions of fractional density (0⊙ 64< ρ< 0⊙ 93) and temperature (1084< T< 1297° C) according to a Newtonian constitutive law commonly used to simulate sintering. The viscosity is suggested to follow In η= a+ Q/RT+ bρ with the values of a= 52⊙ 3±4⊙ 5 and b= 16⊙ 8±0⊙ 2. Q reflects the temperature dependence of η and estimated to be 502±52 kJ mol-1. The sintering stress exhibited almost a constant value in the range of 0·05–0·4 MPa. It is shown that Rahaman's model best fits the experimental results. This paper describes experiments performed on nanostructured WC–Co feedstock to... 

    Pressureless sintering of Ta0.8Hf0.2C UHTC in the presence of MoSi2

    , Article Ceramics International ; Volume 39, Issue 2 , 2013 , Pages 1985-1989 ; 02728842 (ISSN) Ghaffari, S. A ; Faghihi Sani, M. A ; Golestani Fard, F ; Ebrahimi, S ; Sharif University of Technology
    Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000 °C). However, this high melting point makes the ceramic difficult to be sintered at temperatures lower than 2300 °C, pressurelessly. The purpose of this study is to consolidate Ta 0.8Hf0.2C UHTC by pressureless sintering at 2000 °C using MoSi2 as sintering aid. In this regard, effect of different amounts of MoSi2 on sintering behavior of Ta0.8Hf 0.2 UHTC was investigated. It was observed that condensation of the UHTC after sintering at 2000 °C was enhanced by increasing MoSi2 content and the highest relative density of 95% was obtained in the presence of 24 vol.% MoSi2. XRD pattern of the sintered UHTC... 

    Uneven shrinkage causes problems for cheaper hardmetal tooling

    , Article Metal Powder Report ; Volume 66, Issue 5 , 2011 , Pages 29-32 ; 00260657 (ISSN) Simchi, A ; Petzoldt, F ; Hartwig, T ; Veltl, G ; Sharif University of Technology
    Researchers in Germany and Iran have looked at methods of manufacturing wear parts using nanostructured hardmetal combined with a cheaper stainless steel component in pursuit of cost effectiveness. Nanostructured WC-10%Co-0.9%VC and 316L SS powders were used as starting materials. A polymer-wax binder composed of polyethylene copolymer-ethylene vinyl acetate, carnauba wax, paraffin and stearic acid was used to prepare the hardmetal feedstock in a laboratory kneader with z-mixing blades at a temperature of 120°C. The assembled PIM parts were sintered in a laboratory sintering furnace under nitrogen according to different sintering cycles in the temperature range of 1320-1360°C with a heating... 

    Sintering of nanostructured WC-10Co/316L stainless-steel composite parts made by assembling of the PIM parts

    , Article World Powder Metallurgy Congress and Exhibition, World PM 2010, Florence, 10 October 2010 through 14 October 2010 ; Volume 4 , 2010 ; 9781899072194 (ISBN) Simchi, A ; Petzoldt, F ; Hartwig, T ; Veltl, G ; Sharif University of Technology
    European Powder Metallurgy Association (EPMA)  2010
    This paper reports co-sintering response of nanostructured WC-Co/316L stainless steel composite produced by assembling of powder injection molding (PIM) parts. A significant mismatch sintering shrinkage (>4%) was observed in the temperature range of 1080-1350 °C. The reaction between WC and Fe at the contact area resulted in the diffusion of C and Co into the iron lattice and eventually formation of a low-temperature liquid phase that in fact affects the shape control of the PIM parts during sintering. In order to make the co-sintering feasible, a special sintering cycle was developed. The reaction between the cemented carbide and stainless steel was also retarded by developing a special... 

    Physicomechanical properties of spark plasma sintered carbon nanotube-reinforced metal matrix nanocomposites

    , Article Progress in Materials Science ; Volume 90 , 2017 , Pages 276-324 ; 00796425 (ISSN) Azarniya, A ; Azarniya, A ; Sovizi, S ; Madaah Hosseini, H. R ; Varol, T ; Kawasaki, A ; Ramakrishna, S ; Sharif University of Technology
    The technological and industrial needs for development of fully dense nanocomposites have led to significant advances in spark plasma sintering (SPS) technique and its enhanced forms. This technique has opened up a new prospect over carbon nanotube (CNT)-metal matrix nanocomposites (MMNCs) with superior physical or mechanical characteristics. To date, a large number of authentic papers have been published over this ongoing field, but have not been comprehensively reviewed. The pertinent research works cover some significant aspects of CNT-MMNCs requiring a concise review on (i) the potential phase transformations of pure CNTs and microstructure evolution; (ii) the novel approaches for... 

    The densification behavior of metals and alloys during spark plasma sintering: A mini-review

    , Article Science of Sintering ; Volume 51, Issue 2 , 2019 , Pages 1-18 ; 0350820X (ISSN) Sovizi, S ; Esmaeeli Seraji, M ; Sharif University of Technology
    International Institute for the Science of Sintering (IISS)  2019
    As of today, metals and alloys are widely utilized as structural, mechanical, electrical, and magnetic materials in every aspect of technology and industry. The complexity and diversity of metals applications emphasize the need for a new production method to quickly and easily manufacture metallic components. Spark plasma sintering as a new solid-state sintering method has been recently developed to respond to these needs. Up to now, numerous papers and researches have been published in the field of spark plasma sintering and its ability to manufacture metallic samples. Density is a significant property that has a great influence on the physical, mechanical, and functional properties of...