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Various alumina/tungsten carbide based nanocomposites have been fabricated by spark plasma sintering and their wear properties have been investigated by performing ball-on-disk type wear test at room temperature under ambient environment. Our results reveal that the main facture behavior of the Al 2 O 3 /tungsten carbide composites sliding against Al 2 O 3 balls is the plastic deformation. Crack formation and grain pull-out in the wear processes are responsible for lowering the wear rate. The Vickers hardness and toughness values are directly related to wear behavior of the composites that grounds Al 2 O 3 /WC to show lower wear rate on smoothly worn surface. [ABSTRACT FROM AUTHOR]

Abstract: We report the synthesis of a new class of Al2O3–WC nanocomposites for the first time by using metal–organic chemical vapor deposition process in a spouted bed followed by spark plasma sintering technique. The microstructure and mechanical properties of these prepared nanocomposites have been analyzed for various sintering parameters. From microstructure observation, it is found that the nanosized WC particles are dispersed within alumina matrix grains and intergrains. The microstructure of transgranular and step-wise fracture surface are found in these nanocomposites. The basic mechanical properties like density, hardness, and toughness also have been analyzed and the results are interpreted by correlating with that of corresponding microstructures. [Copyright &y& Elsevier]

Abstract: The fine grains of Al2O3–Cr2O3/Cr-carbide nanocomposites were prepared by employing recently developed spark plasma sintering (SPS) technique. The initial materials were fabricated by a metal organic chemical vapor deposition (MOCVD) process, in which Cr(CO)6 was used as a precursor and Al2O3 powders as matrix in a spouted chamber. The basic mechanical properties like hardness, fracture strength and toughness, and the nanoindentation characterization of nanocomposites such as Elastics modulus (E), elastic work (W e ) and plastic work (W p ) were analyzed. The microstructure of dislocation, transgranular and step-wise fracture surface were observed in the nanocomposites. The nanocomposites show fracture toughness of (4.8MPam1/2) and facture strength (780MPa), which is higher than monolithic alumina. The strengthening mechanism from the secondary phase and solid solution are also discussed in the present work. Nanoindentation characterization further illustrates the strengthening of nanocomposites. [Copyright &y& Elsevier]

Abstract: Nanosized chromium carbide has been prepared by metal–organic chemical vapour deposition (MOCVD) method in a fluidized bed and carburized in the mixture of CH4/H2 atmosphere in temperature range 700–850°C. The carburization process involves carbon deposition on the outer surface of the Cr2O3 powder, followed by carbon diffusion into the powder, leading to formation of metastable Cr3C2−x phase and stable Cr3C2. The phase transformation from Cr2O3 to Cr3C2 via an intermediate state Cr3C2−x has been identified using electron-energy loss spectroscopy (EELS) and micro-Raman spectroscopy. We could hypothesize that the formation of carbon nanofilms surrounding the carbide crystallites provides the stress and assist the phase transformation from metastable Cr3C2−x to stable Cr3C2. [Copyright &y& Elsevier]

Abstract: Nanosized particles dispersed uniformly on Al2O3 particles were prepared from the decomposition of precursor Cr(CO)6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr2O3, CrC1−x , and C. A solid solution of Al2O3–Cr2O3 and an Al2O3–Cr2O3/Cr3C2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150°C before hot-pressing at 1400°C, respectively. In addition, an Al2O3–Cr2O3/Cr-carbide (Cr3C2 and Cr7C3) nanocomposite was formed when the particles were directly hot pressed at 1400°C. The interface between Cr3C2 and Al2O3 is non-coherent, while the interface between Cr7C3 and Al2O3 is semi-coherent. [Copyright &y& Elsevier]

Abstract: Nano-scale Cr3C2 powder with an average particle size of 50–80nm, uniformly coated on alumina particles, has been prepared by metal organic chemical vapor deposition (MOCVD) in the fluidized chamber, using the pyrolysis of Cr(CO)6 precursor, and carbothermal treatment in the CH4 and H2 gas mixtures. The Cr(CO)6 precursor was characterized by differential scanning calorimetry (DSC) to understand the decomposition temperature of the precursor, which was determined to be 163°C. The precursor decomposed and formed the mixture of CrC1− x , Cr2O3 and free carbon on the surface of the Al2O3 particles when pyrolyzed in fluidized bed at 300 and 400°C. The resultant powders were examined by X-ray diffractometer (XRD) and transmission electron microscopy (TEM) equipped with energy dispersion spectrometer (EDS), for investigating phase composition and microstructures. The as-deposited particles fabricated at 300 and 400°C in fluidized chamber were amorphous and crystalline, respectively. The thermal behaviour investigated by TG/DTA indicates that the amorphous powder had a exothermic peak in the DTA curve at ∼400°C, which crystallized at this temperature. In order to prepare the nano-particle reinforced composites, the powder fabricated in the fluidized bed was carbonized in the mixed atmosphere of CH4 and H2. Both CrC1− x and Cr2O3 phase were transferred into Cr3C2 phase after the carbothermal treatment. [Copyright &y& Elsevier]