Papers by Keyword: Nanocomposite Powder

Abstract: Composite powder of Fe/Fe₂O₃ type was synthesized by mechanical milling using commercially Fe and Fe₂O₃ powders in mass ratio of 35/65. The milling process leads to the powder homogenization, powder activation and formation of some Fe/Fe₂O₃ composite particles. The Fe/Fe₂O₃ composite powder obtained by mechanical milling and the un-milled Fe/Fe₂O₃ mixture were subjected to the reactive sintering procedure in argon atmosphere at 1100 °C for 6 hours. The sintering procedure promotes the reaction of the Fe with the Fe₂O₃ and the result is a sintered composite compact of Fe/Fe₃O₄/FeO type. The microstructure of the Fe/Fe₃O₄/FeO sintered composite compacts presents iron clusters in an oxide matrix. A more homogeneous iron clusters size and distribution in oxide matrix is observed in the case of the sintered compact obtained from mechano-activated powder. The X-ray diffraction (XRD), laser particles size analysis (LPSA), optical (OM) and scanning electron (SEM) microscopies techniques were used for the investigations.

Abstract: Cr₃C₂-WC-Ni nanocomposite powders with ~50-100 nm were synthesized from precursors by vacuum-aided carbothermal reduction at only 750 °C for 2 h. The phase composition and microstructure of the synthesized products were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The present study shows that Cr₃C₂-WC-Ni nanocomposite powders contain two kinds of solid-solution phases, namely Ni and (Cr, W)₃C₂ solid solution, respectively. WC and W₂C phases do not appear inreaction products due to the dissolution of tungsten atoms into Ni and Cr₃C₂ unit cells. Especially, there is a change of the crystalline structure for (Cr, W)₃C₂ phase from 750 °C to 800 °C.

Abstract: With zirconium oxychloride, aluminium sulphate and titanium oxysulphate as the basic raw materials, zirconia-aluminum titanate nano-composite powders were prepared with the liquid precipitation method. The nanocomposite powders were detected with XRD, TEM and TG-DTA.The results show that recovery ratio of zirconia and aluminum titanate precursosr is higher, with respective pH about 9.5, 5.5 and concentration of 0.1 mol dm^-3 in the system. About several nanometer zirconia and 100 nanometer size aluminum titanate can be obtained when the precursors are respectively roasted at 600°C and 1000°C.

Abstract: The paper presents the experimental work regarding the elaboration of some nanocomposite powders with higher SiC content. For the research, three types of mixtures were prepared: 90SiC-10Al, 70SiC-30Al and 60SiC-40Al using mechanical alloying (MA) technique. The MA was carried out in a vario planetary ball mill Pulverisette 4 for 5 hours using different conditions: - the shock mode (the main disk speed 400 rpm and the planets speed -800 rpm); - the friction mode (the main disk speed 400 rpm and the planets speed 800 rpm). The resulting mixtures was investigated by scanning electron microscopie (SEM), X-ray diffraction pattern (RDX), energy dispersive X-ray analysis (EDAX) and particle size distribution. After 5 hours of MA it is observed that the mixture obtained in the friction mode conditions have a homogenous structure and the particle size distribution is better than the particle size distribution of the mixture obtained in the shock mode conditions.

Abstract: Stainless steel/TiC nanocomposite powder were prepared by high-energy ball-milling method using 316 stainless steel powder, carbon and titanium powder as raw materials. Microstructure of the nanocomposite powder was investigated with XRD and TEM techniques. The results showed that the stainless steel/TiC nanocomposite powder obtained when the ball-milling time was more than 40 hours. DSC analysis method was used to study the characteristics of oxidation resistance and the oxidation reaction kinetics of the nanocomposites powder. Results show that the oxidant resistance of nanocomposite powder was improved, the activation energy of oxidation reaction increased.

Abstract: Mechanical alloying technique was used to produce an intermetallic based composite powder. Mechanical activation of aluminum and nickel oxide powder mixture using a high energy ball mill resulted in a self-propagating high temperature synthesis through which nickel oxide was reduced by metallic aluminum and produced nickel aluminide and alumina composite powder. Effect of milling time on crystallite sizes of the product phases was investigated. The synthesized product was characterized by scanning electron microscope and X-ray diffraction. It was shown that increased milling time resulted in crystallite size reduction and peak broadening in XRD patterns. Calculation of the mean crystallite sizes of the product phases indicated that they are in nano scale. The results were further confirmed by transmission electron microscopy.

Abstract: Nanocomposite WC-10Co powder produced by spray pyrolysis-continuous reduction & carbonization technology and cubic boron nitride (CBN) plated with titanium by vacuum vapor deposit were used, and this paper adopted spark plasma sintering (SPS) process to prepare CBN enhanced ultrafine WC-10Co cemented carbide cermets composite material. The microstructure and mechanical properties of CBN-WC-10Co composites were investigated. The results show that CBN-WC-10Co composites consolidated by spark plasma sintering can reach 95.0 % relative density, and transverse rupture strength (TRS) is 1050 MPa, the average grain size of cermets matrix is less than 420 nm, and CBN-WC-10Co composites with excellent properties are achieved. The CBN still remains very good crystal shape after 1240°C spark plasma sintering, and there is not obvious clearance between CBN plated with titanium and the cermets matrix, the coated titanium layer can not only improve the thermal stability of CBN, but also increase the properties of CBN-WC-10Co composites.

Abstract: WC-10Co nanocomposite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of ball-milled time on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that ultrafine WC-10Co cemented carbides can reach 99.79% relative density, and transverse rupture strength is more than 3750MPa, Rockwell A hardness is more than 92.6, the average grain size is less than 440 nm, when ball-milled time is 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and fine microstructure is obtained. The optimum ball-milling time is 48 hours.

Abstract: WC-10Co nanocomposite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of ball-milled time on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that ultrafine WC-10Co cemented carbides can reach 99.79% relative density, and transverse rupture strength is more than 3750MPa, Rockwell A hardness is more than 92.6, the average grain size is less than 440 nm, when ball-milled time is 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and fine microstructure is obtained. The optimum ball-milling time is 48 hours.

Abstract: Structure investigation results for MASHS powder Fe40Al/Al2O3 are presented. The powder structure formation proceeds via two stages. On the first step (mechanical activation) aluminothermal reaction takes plays in the system Fe+Al+Fe2O3, leading to formation of nanocomposite precursor Fe-Al-Al2O3. On the second step (SHS), iron and aluminum reacts, forming intermetallic FeAl. As-synthesized composite powder completely inherits the precursor structural morphology in spite of the phase transformations taking place during the production process. Such a production route provides the formation of intergrowth nanocomposite material structure with improved interfacial strength.