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Liu Y.,Sichuan University | Liu Y.,Southwest Jiaotong University | Wang X.-M.,Southwest Jiaotong University | Cen S.-B.,Southwest Jiaotong University | And 5 more authors.
Rare Metals | Year: 2014

A series of the electrochemical and long-term corrosion tests was carried out in a 3.5 wt% Na2SO4 solution on thermal-sprayed WC-17Co and WC-10Co-4Cr cermet coatings in order to examine the effect of composition of binder materials on the corrosion behavior. The results reveal that the overall corrosion resistance of the WC-17Co coating is inferior to that of the WC-Co-Cr coatings due to the corrosion of binder materials which induce WC particles to fall off. CoO and WO3 oxide films form on the surface of WC-17Co coating in Na2SO4 solution electrochemical corrosion process, which will protect the coating in the process of corrosion. Cr2O3 oxide film formed on the WC-10Co-4Cr coating surface has a strong hindered role to corrosion. The corrosion mechanism of WC-17Co coating in Na2SO4 solution is entire corrosion of Co matrix, while it is film-hole corrosion mechanism for WC-10Co-4Cr coating. © 2014 The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg. Source


Wang L.-J.,Southwest Jiaotong University | Qiu P.-X.,Southwest Jiaotong University | Liu Y.,Southwest Jiaotong University | Zhou W.-X.,Zigong Tungsten Carbide Co. | And 2 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2013

A series of electrochemical and long-term corrosion tests were carried out in a neutral saline (5% NaCl) vapor of 35 °C on thermal sprayed WC cermet coatings containing different kinds of metallic binders in order to examine the effect of composition of binder materials on the corrosion behavior. The experimental results revealed that the overall corrosion resistance of WC-Co coating was inferior to that of WC-Co-Cr coating. For the coatings without Cr, WC-Co, general corrosion occurred in binder materials in addition to galvanic corrosion between WC particles and metallic binders in the neutral environment. By contrast, the formation of passive film in the form of surface oxide in the coatings containing Cr, WC-Co-Cr, suppressed the binder and metallic binders to be eroded. It is found that the chemical composition of metallic binder materials is one of the important factors influencing the corrosion resistance of HVOF sprayed WC cermet coatings in the neutral vapor. Source


Liu X.,Beijing University of Technology | Wang H.,Beijing University of Technology | Song X.,Beijing University of Technology | Wang X.,Beijing University of Technology | Li Y.,Zigong Tungsten Carbide Co.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2016

WC-Co composite powder was synthesized with carbon black and W, Co oxides as raw materials and VC as additive by the in-situ reduction and carbonization process. The nanocrystalline WC-Co alloys were fabricated by the spark plasma sintering technique using the prepared WC-Co composite powder. The phase composition, microstructure characteristics and mechanical properties of the sintered cemented carbides were analyzed. The results show that VC addition plays a significant role in phase composition, grain size and properties of the prepared WC-Co alloy. When the VC addition is 2.0%, the average grain size is 101 nm, the phases are WC and Co, and the cemented carbides possess high hardness and good fracture toughness. © 2016, Science Press. All right reserved. Source


He Y.-L.,Central South University | Long A.-P.,Central South University | Zhou W.-X.,Central South University | Zhou W.-X.,Zigong Tungsten Carbide Co. | And 3 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2014

4.5%Y2O3-ZrO2, 0.6%Sc2O3-YSZ composite ceramic nanopowders were prepared by chemical co-precipitation method in ethanol/water (the volume ratio of alcohol to aqueous is 5:1) using ZrOCl2 .8H2O, Y(NO3)3·6H2O, Sc2O3 as raw materials and polyethyleneglycol (PEG) as dispersant. The synthesized powders were characterized by means of TEM and XRD analysis. High temperature stability of composite ceramic nanopowders was also studied. The results show that, after calcined at 600°C for 2 h, the presynthesized powders show the pure noneequilibrium tetragonal structure, the size of 0.6%Sc2O3-YSZ particles prepared by reverse titration method is ~20 nm compared with~30 nm prepared by the straight titration method. After sintered at 1 200°C for 100 h, YSZ shows equilibrium tetragonal structure together with cubic phase; after sintered at 1 300°C for 100 h, the equilibrium tetragonal structure partly transforms to cubic phase and a small amount of monoclinic phase; after sintered at 1 400°C for 100 h, the tetragonal structure transforms to cubic and monoclinic phase entirely. Whereas, 0.6%Sc2O3-YSZ keeps the pure noneequilibrium tetragonal structure after sintered at 1 200, 1 300 or 1 400°C for 100 h. Therefore, the high temperature phase stability of YSZ can be modified by addition small fraction of Sc2O3. Source


Zhou W.-X.,Zigong Tungsten Carbide Co. | Li Y.-X.,Zigong Tungsten Carbide Co. | Li S.-L.,Central South University | Yi C.-B.,Zigong Tungsten Carbide Co. | Yan W.,Zigong Tungsten Carbide Co.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2013

Three WC10Co4Cr coatings were prepared by high velocity oxygen fuel (HVOF) spray with various spraying distance (380, 340 and 300 mm) using agglomerated and sintered WC10Co4Cr powder with particle size range of -45~+15μm. The coatings properties were characterized by means of optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness measurements and so on. The results indicate that with the spray distance decrease, WC10Co4Cr coating's porosity decreases, microhardness increases, abrasive wear resistance enhances; spray distance from 300 mm to 380 mm has slightly effect on phase nature of the coatings, WC, W2C and small amount of amorphous phase are detected in the three sprayed coatings; spray distance from 300 mm to 340 mm has slightly effect on coatings microhardness and abrasive wear resistance. Abrasive wear mechanism and effect of different spray distance on the abrasive wear resistance properties of the WC10Co4Cr coating were also discussed, combining with the microstructure of the central site of wear area, the physical property of the spray and the changement of the surface roughness. Source

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