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Now showing items 1 - 5 of 5

  • Microstructure and oxidation behavior of Ti(C,N)-based cermets with in situ synthesized Ni 3 Al phase

    Qi, Kaifeng   Yang, Mei   Li, Shenhou   Liu, Junbo   Li, Tijun   Ye, Junliu  

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  • Microstructural changes of (Ti,W)C solid solution induced by ball milling

    Yang, Mei   Guo, Zhixing   Xiong, Ji   Liu, Fujiao   Qi, Kaifeng  

    The effect of ball milling on microstructural change of (Ti,W)C solid solution was investigated. In addition to the particle size reduction with milling time, detailed studies using the X-ray diffraction line profiles were carried out to evaluate the microstructural parameters, including lattice parameter, crystallite size and microstrain. Nelson Riley extrapolation and Williamson-Hall method are employed. The results suggest lattice expansion, with the lattice parameter increasing from 43212 A to 43241 A. The defects and surface stress generated during ball milling are deemed to be responsible for the increased d-spacing of (Ti,W)C solid solution with milling time. The crystallite size displays a diminishing trend with increasing milling time, which is consistent with the SEM observation. However, the microstrain developed is tensile in nature and firstly increases with up to 36 h milling, and then the strain reduces for further milling perhaps due to the strain relaxation by the formation of dislocations. (C) 2017 Elsevier Ltd. All rights reserved.
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  • Surface modification of WC-based cemented carbide by one-pot non-vapor deposition method derived Al2O3 coatings

    Yang, Mei   Guo, Zhixing   Qi, Kaifeng   Zhong, Hai   Deng, Jianxiong   Liu, Jia   Long, Jianping  

    Al2O3 films are usually coated on WC-based cemented carbide by chemical/physical vapor deposition techniques. In the paper, a novel one-pot non-vapor deposition method is introduced, which is achieved by dip-coating of Al2O3 sot on the cemented carbide green compact and following liquid phase sintering. Tile coated surface is mainly composed of 0.5 sm Al2O3 fine grains embedded with 2 pm rounded edged WC particles. The Co capping phenomenon on the surface of cemented carbide disappears after coating, which is attributed to the carbon-deficit condition created by the dip-coating process. Simultaneously, the introduction of Al2O3 results in a W-rich Co binder, which facilitates the transformation of WC shape to round-edged shape on the surface compared with the faceted truncated triangular prism shape in inner area. There is hardness increase and transverse rupture strength decrease after Al2O3 coating, which is attributed to the existence of W3Co3C on the surface. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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  • Microstructure and oxidation behavior of Ti(C,N)-based cermets with in situ synthesized Ni3Al phase

    Qi, Kaifeng   Yang, Mei   Li, Shenhou   Liu, Junbo   Li, Tijun   Ye, Junliu  

    Ni3Al phase was synthesized by in-situ reaction of Ni binder and AlN addition during liquid phase sintering. The microstructure and properties of the Ni3Al-containing Ti(C,N)-based cermets were investigated. The hardness of the cermet increased after addition of 2.5 wt%AlN due to the solid-solution strengthening effect of Ni3Al, and further addition of AlN yielded coarser core-rim grains and decrease of hardness. The transverse rupture strength declined rapidly after addition of 5 wt% AlN, which was attributed to the increase of porosity. After static oxidation at 900 degrees C, the mass gain of the cermet without AlN addition increased rapidly with oxidation time and followed a quasi-parabolic law. After addition of 2.5 wt%AlN, both mass gain and oxidation rate declined obviously, and the oxidation kinetics curve still presented a quasi-parabolic law. The mass gain increased slightly after addition of 5.0 wt% AlN, and larger addition of AlN up to 7.5 wt% resulted in the changing of oxidation kinetics to a linear law. At 900 degrees C, the Ti(C,N)-based hard phase and Ni binder phase in the cermet all suffered serious oxidation. The Ti(C,N)-based hard phase was mainly oxidized to TiO2, and Ni binder transformed to complex oxides such as Ni3TiO7 and NiTiO3. As for the cermet with 2.5 wt% AlN addition, the oxidation behavior showed much difference. Though Ni3Al-containing binder was oxidized to Ni3TiO7 and NiAl2O4, both the intermediate oxidation product of Ti(C,N) hard phase, i.e. Ti(O-0.12,C-0.53,N-0.32) and Ni3Al remained stable after dwelling for 4 h. The oxide layer on the cermet with 2.5 wt% AlN addition appeared to be dense and protective, which inhibited the diffusion of oxygen into the cermet and improved the oxidation resistance of the cermets.
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  • Microstructure of TiC-Based Coatings on Cemented Carbide Derived by Sol-Gel Routes

    Yang, Mei   Guo, Zhixing   Qi, Kaifeng   Huang, Kun   Deng, Jianxiong   Liu, Jia  

    TiC-based coating is prepared by depositing TiO2 sol on cemented carbide compact and liquid phase sintering. TiC forms due to carbothermal reduction reaction of TiO2 and then reacts with WC and transforms to TiC-based solid solution. Ti content changes the WC growth mechanism and results in the multi-stepped morphology. When sintered cemented carbide is used as substrate, WC keeps the equilibrium truncated triangle prism morphology due to the relatively weak diffusion among Ti, WC, and Co.
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