M. Ashraf Imam

Chestnut Hill College, Chestnut Ridge, New York, United States

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Publications (75)74.76 Total impact

  • Powder Metallurgy 04/2014; 57(2):147-154. DOI:10.1179/1743290113Y.0000000082 · 0.60 Impact Factor
  • Industrial Crops and Products 11/2013; 51:158-162. DOI:10.1016/j.indcrop.2013.09.004 · 3.21 Impact Factor
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    ABSTRACT: The present work demonstrates that high pressures alone can initiate and drive densification in nanopowder magnesium aluminate compacts without the application of temperature. The high-pressure processed nanostructured ceramic has a Vickers hardness of 182 and transmits in the infrared and visible wavelengths. The lack of externally applied thermal energy during densification enables the exploration of room temperature diffusion processes confined to nanoparticle surfaces that result in a bulk ceramics with grain sizes equal to the powder particle size. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
    Scripta Materialia 08/2013; 69(4-4):334-337. DOI:10.1016/j.scriptamat.2013.05.014 · 2.97 Impact Factor
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    ABSTRACT: Mg-Ti alloys are attractive for structural applications because of low density and improved corrosion resistance by selective oxidation including hydrogen storage and switchable mirror applications. Titanium has a melting point (1670°C) that greatly exceeds the boiling point of magnesium (1090°C) and therefore, alloying of Mg and Ti by conventional methods is extremely difficult. Secondly, the solubility of Ti in liquid Mg is very low and it is difficult to extend solubility by rapid solidification. Physical vapor deposition by electron beam deposition and magnetron co-sputtering has been used to extend the solubility of Ti in Mg. Mechanical alloying and anvil-cell processing at extreme temperatures and pressures have also used to enforce alloying of Mg with Ti. The present paper deals with the consolidation of blended magnesium-titanium powders by microwave heating, an approach that appears highly cost effective.
    Key Engineering Materials 05/2013; 551:73-85. DOI:10.4028/www.scientific.net/KEM.551.73 · 0.19 Impact Factor
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    ABSTRACT: The major reason that there is not more widespread use of titanium and its alloys is the high cost. In this paper, developments in one cost effective approach to fabrication of titanium components - powder metallurgy - will be discussed under various aspects of this technology. The aspects to be discussed are the blended elemental approach, pre-alloyed techniques, additive layer manufacturing, metal injection molding, spray deposition and microwave sintering. A brief review of a number of low cost powder production processes is also presented.
    Key Engineering Materials 05/2013; 551:3-10. DOI:10.4028/www.scientific.net/KEM.551.3 · 0.19 Impact Factor
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    ABSTRACT: Samples of rice husks were transformed to β (3C)-SiC by microwave processing in controlled conditions of temperature and vacuum. This simple and fast way of producing powdered samples of silicon carbide is technologically important if this material is to be used for electronics, sensors, biotechnology, and other applications. Using x-ray diffraction it was found that the microwave processed sample at 1900 °C consists of β (3C)-SiC phase. Raman scattering measurements confirmed the formation of β (3C)-SiC phase. Transmission electron microscopy revealed the presence of stacking faults along the [111] direction. The presence of 6H/4H stacking faults in 3C phase is explained in terms of their total energies. The presence of these stacking faults with a ∼1 eV band offset between the host 3C and hexagonal stacking faults implies that these stacking faults provide a conduction barrier, and the interfaces between the stacking faults and host lattice act as a heterojunction that may provide potential utility for various optoelectronic applications.
    Journal of Applied Physics 04/2012; 111(7). DOI:10.1063/1.3702582 · 2.19 Impact Factor
  • M. Ashraf Imam
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    ABSTRACT: The International Conference on Titanium was begun in 1968 to assess the national significance attached to the development of titanium in relation to the technical needs of the participating countries. The conference, held every four years, attracts strong international participation. This article reviews the 12th World Conference on Titanium, hosted by the Nonferrous Society of China and held in Beijing, China, 19–24 June 2011.
    JOM: the journal of the Minerals, Metals & Materials Society 10/2011; 63(10):16-23. DOI:10.1007/s11837-011-0166-3 · 1.40 Impact Factor
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    ABSTRACT: The isothermal oxidation behavior and thermal stability of a cobalt base alloy was investigated up to a period of 312 hr in air from 1000 to 1200 degrees C. A comparison of oxidation behavior of this alloy with a conventional nickel-base superalloy (Inconel 713C) has been conducted in detail. This experimental alloy oxidizes by forming layers of Al2O3, Cr2O3, TiO2, CoO and traces of SiO2 with WO2 oxides on the surface of the specimen in contact with air. Scanning electron microscopy (SEM) was used to study the microstructure, morphology and compositions of oxides formed after the exposure. Thermal stability of the alloy after extended periods of exposures to air at 1000, 1100 and 1200 degrees C was studied using transmission electron microscopy (TEM).
    Materials Science Forum 06/2010; DOI:10.4028/www.scientific.net/MSF.654-656.550
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    ABSTRACT: Millimeter-wave sintering of ceramic laser host materials has been under investigation for high-energy laser (HEL) applications. Advantages of polycrystalline, compared to single-crystal, laser host materials include lower processing temperature, higher gain from higher dopant concentration, cheaper fabrication, and larger devices. We are currently investigating the solid-state reactive sintering of neodymium-doped yttrium aluminum garnet (Nd:YAG) using a high power millimeter-wave beam as the heat source. The 83 GHz beam is generated in the Naval Research Laboratory (NRL) High Frequency Materials Processing Facility that is powered by a 15 kW, CW, 83 GHz GYCOM gyrotron. The starting powder is a mixture of commercially available alumina, yttria, and neodymia powders. Near transparency and over 99% theoretical density have been achieved with grain sizes of 5 to 10 mu m. The fluorescence lifetime of the Nd+3 1.06 mu m lasing transition was measured to be about 200 mu s, in good agreement with other work. SEM studies of the sintered microstructure show residual porosity caused by trapped pores that must be eliminated to produce fully transparent material.
    Materials Science Forum 06/2010; DOI:10.4028/www.scientific.net/MSF.654-656.2002
  • F. H. (Sam) Froes, M. Ashraf Imam
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    ABSTRACT: Titanium is the "wonder" metal, which makes sense as the material of choice for a wide variety of applications. However, because of its relatively high price- a result of extraction and processing costs- it is used basically only when it is the only choice; with the caveat that titanium has a bright "image" which can lead to use even when the economics are unfavorable. The major thrust in the area of titanium technology has been aimed at achieving cost reduction rather than developing alloys with enhanced properties. This paper will overview the potential areas which are amenable to cost reduction and present some applications of titanium and it's alloys.
    Key Engineering Materials 05/2010; 436:1-11. DOI:10.4028/www.scientific.net/KEM.436.1 · 0.19 Impact Factor
  • M. Ashraf Imam, F. H. Sam Froes
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    ABSTRACT: There are a number of maturing extraction and fabrication techniques which can potentially reduce the cost of titanium. These are in part responsible for a number of developing applications for titanium.
    JOM: the journal of the Minerals, Metals & Materials Society 05/2010; 62(5):17-20. DOI:10.1007/s11837-010-0069-8 · 1.40 Impact Factor
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    ABSTRACT: The emerging reduction technologies for titanium from ore produce powder instead of sponge. Conventional methods for sintering and melting of titanium powder are costly, as they are energy intensive and require high vacuum, 10(-6) Torr or better, since titanium acts as a getter for oxygen at high temperature, adversely affecting mechanical properties. Other melting processes such as plasma arcs have the additional problem of electrode consumption, and direct induction heating of the titanium powder is problematic. Microwave sintering or melting in an atmospheric pressure argon gas environment is potentially cost effective and energy efficient due to the possibility of direct microwave heating of the titanium powder augmented by hybrid heating in a ceramic casket. We are investigating this approach at the Naval Research Laboratory using an S Band microwave system. The experimental setup and the results of melting and sintering experiments will be described including a rough estimate of energy usage.
    Key Engineering Materials 05/2010; 436:131-140. DOI:10.4028/www.scientific.net/KEM.436.131 · 0.19 Impact Factor
  • M. Ashraf Imam, F. H. Sam Froes
    JOM: the journal of the Minerals, Metals & Materials Society 05/2010; 62(5):15-16. DOI:10.1007/s11837-010-0068-9 · 1.40 Impact Factor
  • M. Ashraf Imam, F. H. Froes, Kathleen L. Housley
    Kirk-Othmer Encyclopedia of Chemical Technology, 03/2010; , ISBN: 9780471238966
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    ABSTRACT: We are investigating the solid-state reactive sintering of polycrystalline Nd:YAG ceramic laser host materials using a high power millimeter-wave beam as the heat source. The starting powder is a mixture of commercially available alumina, yttria, and neodymia powders. The laser-quality results obtained using the solid-state reactive sintering approach and the same materials in a conventional vacuum furnace(1) provide a benchmark for our experiments, which are being carried out using the Naval Research Laboratory (NRL) 83 GHz Gyrotron Beam Material Processing Facility. One objective of our work is to determine the effect of millimeter-wave heating on processing variables such as temperature and hold time and on the microstructural properties impacting the laser host application. Another objective is to optimize the heating uniformity and efficiency of the process for future use in a manufacturing process. Initial experiments with 1-hour hold times have produced translucent samples whose microstructure is currently being evaluated. Longer processing times (up to 16 hours) were needed to achieve full transparency in a conventional furnace. Hold times longer than 1 hour were also investigated and will be reported.
    Advanced Processing and Manufacturing Technologies for Structural and Multifunctional Materials III, 01/2010: pages 1 - 10; , ISBN: 9780470584392
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    ABSTRACT: The emerging reduction technologies for titanium from ore produce powder instead of sponge. The processing of titanium powder by conventional methods is energy intensive. Titanium acts as a getter for oxygen and tends to react with many materials at the high melt temperature (melting point: 1675°C). Most melts conventionally require high vacuum, 10-6 Torr or better. Plasma arcs have the additional problem of electrode consumption, and direct induction heating of the titanium powder is problematic. Microwave melting in an inert gas environment is potentially energy efficient due to the possibility of direct microwave heating of the titanium powder augmented by hybrid heating. A robust S-Band microwave system has been developed for melting titanium powder compacts up to few hundred grams in mass. The titanium powder compacts are heated to temperatures up to 1800°C in an over-moded cylindrical cavity with a flowing argon gas atmosphere. Microwaves from a 6 kW Cober S6F industrial microwave generator are injected along the cavity axis and a 3-stub tuner is used to optimize coupling efficiency. The compact is contained in a ceramic crucible surrounded by an insulating casket. Plasma formation during processing has been observed, produced by either breakdown of the argon atmosphere (blue light emission) or by titanium vapor reacting with residual oxygen (yellow light emission). The experimental setup and the results of melting and sintering experiments will be described.
    IEEE International Conference on Plasma Science 01/2010; DOI:10.1109/PLASMA.2010.5533956
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    ABSTRACT: We present results on microwave, millimeter-wave, and millimeter-wave-driven plasma-assisted processing of materials. The research is primarily based on two systems- a 2.45 GHz, 6 kW S-band system and an 83 GHz, 15 kW gyrotron-based quasi-optical system. The S-Band system is used to synthesize nanophase metals, metal mixtures, and metal oxides by our patented continuous microwave polyol process, which has potential for large scale and low cost production. This system is also being investigated to develop techniques for titanium melting and sintering. The 83-GHz system is used for rapid sintering of ceramic powder compacts to produce polycrystalline materials with limited grain growth. An important application is to the development of polycrystalline laser host materials for high power solid-state lasers, where the requirement is for transparency with high optical quality and good lasing efficiency. We are currently investigating solid-state reactive sintering of Nd-doped YAG (Yttrium Aluminum Garnet) from commercial oxide powders. This has thus far yielded translucent samples with good fluorescence lifetime of the lasing state. Techniques for further reducing light scattering by residual pores are being investigated. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, as the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition systems. The results and implications of this wide range of materials processing experiments are presented and discussed.
    Materials Science Forum 01/2010; 638-642:2052-2057. DOI:10.4028/www.scientific.net/MSF.638-642.2052
  • Chandra S. Pande, M. Ashraf Imam
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    ABSTRACT: Formation of annealing twins and its relation to grain growth is investigated. Our previous studies have established a relation between twin density, grain size, and temperature. A model of the mechanism of their formation based on the emergence of Shockley partial loops on consecutive {111} planes during grain migration has also been developed previously. This model can satisfactorily explain some experimental and theoretical results found over the years. In this paper we provide additional experimental evidence in support of our model by investigating twin formation in boron-doped nickel. We find that boron addition slows down grain growth, though the kinetics of grain growth remains parabolic. There is a drastic reduction in twin density due to boron addition especially around a boron content of ∼200ppm.
    Materials Science and Engineering A 06/2009; 512(1):82-86. DOI:10.1016/j.msea.2009.01.030 · 2.41 Impact Factor
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    ABSTRACT: The continuous microwave polyol process is a promising novel approach to the synthesis of metallic and ceramic nanopowders Current efforts are directed toward synthesizing ytterbia-doped yttria (Yb2O3 Y2O3) for use as a polycrystalline laser host material The process involves pumping a mixture of yttrium nitrate and ytterbium nitrate dissolved in hydrated diethylene glycol through a pressurized quartz tube contained in an S Band waveguide driven by a 2 45 GHz microwave source at powers up to 6 kW As the solution moves along the waveguide it absorbs the co propagating microwave energy and is heated rapidly to a temperature above 200 degrees C causing a reaction to occur Condensation reactions then form particles with ytterbium doped yttria crystal structure The rapid heating and cooling serve to limit the growth of the crystals so that they are on submicron and fairly uniform in size The production of doped yttria was confirmed by x-ray diffraction
    Processing and Properties of Advanced Ceramics and Composites, 05/2009: pages 1 - 14; , ISBN: 9780470522189
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    ABSTRACT: Millimeter-wave sintering of ceramic laser host materials has been under investigation at the Naval Research Laboratory (NRL) for high-energy laser (HEL) applications. Potential advantages of polycrystalline, compared to single-crystal, laser host materials include lower processing temperature, higher gain from higher dopant concentration, cheaper fabrication, and larger devices. Successful production of laser quality polycrystalline laser host requires a high purity material and the sintering process must achieve nearly perfect micro structure as imperfections quickly result in unacceptable light absorption and scattering. Transparent, laser quality, polycrystalline Nd:YAG has recently been achieved in conventional vacuum furnaces using a reactive sintering process based on commercially available powders, and we have been trying to replicate these results in the NRL millimeter-wave materials processing facility. Compacts prepared from mixtures of the oxide precursors are placed in an open or closed crucible in a vacuum environment and are heated directly by the 83 GHz beam to temperatures of 1000- 1800degC. Over 99% theoretical density has been achieved at the highest temperatures with moderate grain growth. Fluorescence lifetime studies of the Nd+3 ion are in good agreement with published results for laser quality material. Our X-ray diffraction studies of the phases present at various temperatures are generally in agreement with previous work. However, full transparency has not been achieved and investigation of the sintered compact microstructure has revealed trapped pores and other imperfections. There has also been unexpected variability in the results. New modeling results for the open casket configuration, which was chosen for temperature measurement and heating efficiency considerations, indicate that large thermal gradients are likely. These gradients can produce non-uniform sintering and complicate temperature measurements. New closed casket configuration- s are being developed that are expected to result in smaller thermal gradients and more accurate temperature measurement while retaining good heating efficiency. The results of model calculations and available experimental results will be discussed.
    IEEE International Conference on Plasma Science 01/2009; DOI:10.1109/PLASMA.2009.5227630