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Zhang L.,Hefei University of Technology | Zhang M.,Anhui Derun Industrial Equipment Co Ltd | He X.-N.,Anhui Derun Industrial Equipment Co Ltd | Tang W.-M.,Hefei University of Technology
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2015

SiC ceramics were fabricated through pressureless sintering at temperature below 1600℃ in air by adding Al2O3-Y2O3-CaO sintering additives. Effects of SiC particle size and gradation, binder content, sintering additive content, forming pressure and sintering temperature on microstructure and properties of the SiC ceramics were investigated. The results show that during sintering, the sintering-aiding melt forms and fills into the pores of the sintering bodies. And then, it mainly changes into the crystalline oxides along the SiC particles in the next cooling process. It can effectively promote the sintering densification and improve the microstructure and properties of the SiC ceramics. The SiC ceramics sintered at 1575℃ have a density of 2.93 g/cm3 and a bending strength of 359 MPa, using the 3.5 μm and 0.5 μm SiC powders at a mass ratio of 3:1 as raw materials and adding 30 mass% sintering additives. ©, 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.


Zhang L.,Hefei University of Technology | Fang M.,Hefei University of Technology | Zhang M.,Anhui Derun Industrial Equipment Co. | He X.N.,Anhui Derun Industrial Equipment Co. | Tang W.M.,Hefei University of Technology
Materials Research Innovations | Year: 2015

Silicon carbide (SiC) matrix composites have been obtained through liquid-phase sintering in air at temperature below 16008C by adding three kinds of sintering additives, i.e. BaO-Al2O3, BaO- Al2O3-Y2O3 and BaO-Al2O3-CaO, respectively. Effects of type and content of the sintering additive on microstructures and mechanical properties of the composites were investigated. Among these three types of sintering additives, BaO-Al2O3-Y2O3 system was determined to be the most effective. Densification occurs in the sintering process, during which a liquid-phase melt forms through reaction between the sintering additives and SiO2 (the oxidation product of SiC). The melt mostly transforms into crystalline oxides, which act as secondary phases and construct a strong bonding interface by connecting with the SiC particles tightly. By adding 30 wt-% BaO-Al2O3-Y2O3 sintering additives, bending strength and fracture toughness of the SiC composites sintered at 15508C are up to 520 MPa and 6.7 MPa m1/2, respectively. © W. S. Maney & Son Ltd 2015.


Zhang L.,Hefei University of Technology | Zhang M.,Anhui Derun Industrial Equipment Co. | He X.,Anhui Derun Industrial Equipment Co. | Tang W.,Hefei University of Technology
Journal of Materials Engineering and Performance | Year: 2016

The corrosion behavior of the liquid-phase sintered SiC (LPS-SiC) was studied by dipping in 3.53 mol/L HNO3 aqueous solution at room temperature and 70 °C, respectively. The weight loss, strength reduction and morphology evolution of the SiC specimens during corroding were revealed and also the chemical corrosion process and mechanism of the SiC specimens in the acidic solution were clarified. The results show that the corrosion of the LPS-SiC specimens in the HNO3 solution is selective. The SiC particles are almost free from corrosion, but the secondary phases of BaAl2Si2O8 (BAS) and Y2Si2O7 are corroded via an acid-alkali neutralization reaction. BAS has a higher corrosion rate than Y2Si2O7, resulting in the formation of the bamboo-leaf-like corrosion pits. As the SiC specimens etched in the HNO3 solution at room temperature for 75 days, about 80 μm thickness corrosion layer forms. The weight loss and bending strength reduction of the etched SiC specimens are 2.6 mg/cm2 and 52%, respectively. The corrosion of the SiC specimens is accelerated in the 70 °C HNO3 solution with a rate about five times bigger than that in the same corrosion medium at room temperature. © 2016 ASM International


Zhang L.,Hefei University of Technology | Mao X.,Hefei University of Technology | Chen G.,Anhui Electrical Power Research Institute | Zhang M.,Anhui Derun Industrial Equipment Co. | And 2 more authors.
Corrosion Engineering Science and Technology | Year: 2016

Corrosion behaviour of the liquid-phase sintered SiC ceramics (LPS-SiC) was studied through exploration of weight loss, strength reduction and morphology evolution of the SiC specimens etched in the room-temperature/70°C 6.12 mol/L (20 wt-%) NaOH aqueous solutions. As a comparison, corrosion of the reaction-bonded SiC ceramics (RB-SiC) was also investigated. The results show that corrosions of the SiC specimens mainly contain homogeneous dissolution of the secondary-phase oxides in the LPS-SiC and that of Si in the RB-SiC, and peel-off of the SiC particles, resulting in increase of the surface roughness, weight loss and strength reduction of the SiC ceramics. As dipped in the 70°C NaOH solution, corrosion pores and channels form in the sublayer, leading to rapid increase of weight loss and strength reduction of the LPS-SiC. No matter in the room-temperature or 70°C NaOH solution, the LPS-SiC always has a higher corrosion resistance than the RB-SiC. © 2016 Institute of Materials,Minerals and MIining

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