Papers by Keyword: Pressureless Sintering

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Authors: Ming Liang Li, Hai Long Wang, Rui Zhang, Jing Li, Jun Hao Li
Abstract: SiC powders with nickel powders and sintering aids were prepared by pressureless sintering at 1500oC under a N2 atmosphere. XRD, TEM, SEM techniques were used to characterize the phases and microstructure of the specimens. The thermoelectric properties of SiC matrix composites were investigated by measuring the Seebeck coefficient and the electrical conductivity. The main phase of all samples was -SiC, the Ni2Si can be observed with adding nickel powders. The largest electric conductivity was close to 3.5 m-1-1 at about 973K. The highest Seeback coefficient was up to 1800 V/K at 1073K. The transition from n-type to p-type was occurred.
Authors: Chang Ling Zhou, Yan Yan Wang, Zhi Qiang Cheng, Chong Hai Wang, Jie Fan, Cheng Gong Sun, Bao Lin Feng
Abstract: ZrB2-SiC and ZrB2-SiC-C ultra-high temperature ceramics (UHTCs) were fabricated by pressureless sintering under an argon atmosphere. The mass and linear ablation rates were tested in an oxyacetylene flame with high velocity. The microstructure and phase transformation of the ZrB2-based UHTCs were characterized by scanning electron microscopy along with energy dispersive spectrometry. Results show that the UHTCs have excellent properties of ablation resistance at ultra-high temperature. The values of mass and linear ablation rates were lower in the ZrB2-SiC UHTCs than those measured for ZrB2-SiC-C. The effect of C addition on the ablation resistant was not obvious but it influenced the microstructure of the ZrB2-SiC UHTCs. And the ablation resistant mechanisms of ZrB2-based UHTCs were discussed according to microstructure analysis.
Authors: Peng Yuan Yang, Yu Hong Chen, Bin Chen
Abstract: The low-cost production and performance of 6061-aluminium alloy matrices reinforced with coated silicon carbide particulate has been studied. The micro-wave vacuum sintering was adopted to prepare the composite in order that the loss ignition is very small. The effect of copper coated silicon carbide has proved beneficial to interfacial bonding and improved the mechanical properties. Differences in the fracture characteristics of specimens containing coated and non-coated particles were observed. The particulates size has much influence on mechanical properties.
Authors: Lev N. Rabinskiy, Sergey A. Sitnikov, Veniamin A. Pogodin, Andrey A. Ripetskiy, Yury O. Solyaev
Abstract: This article presents the results of the binder jetting technology application for the silicon nitride ceramics production. A modified version of the Plan-B 3D printer with an epoxy-based binder was used for silicon green bodies preforming. Silicon powder was pre-coated with epoxy resin, and the curing agent was added during 3-D printing of green bodies using a standard cartridge. Curing and removal of organics was carried out during the high-temperature vacuum drying of the printed preforms. Reaction-bonded silicon nitride was obtained by using pressureless sintering. An additional compaction of green bodies is proposed to reduce the porosity of green bodies and sintered ceramics. It is shown that the proposed methods allows to improve the mechanical properties of sintered specimens.
Authors: Jian Guang Xu, Shi Bo Guo, Jian Hui Yan, Da Gong Zhang
Abstract: Si3N4 particle reinforced MoSi2 composite powder has been successfully synthesized combustion synthesis method. XRD and SEM results showed that the combustion product was mainly composed by MoSi2 and Si3N4. The as-prepared Si3N4/MoSi2 composite powder has been pressureless sintered at 1600°C for 1h. The microstructure and mechanical properties of the composite were investigated. Relative densities of the monolithic material and composite were 92.2% and 89.6%, respectively. The composite has higher Vicker’s hardness and flexural strength than monolithic MoSi2. Especially the room-temperature fracture toughness of the composite is from 4.21MPa•m1/2 for MoSi2 to 7.25MPa•m1/2 for composite, increased by 72.2%, respectively. The morphology of fractured surface of composite revealed the mechanism of improving mechanical properties of MoSi2 matrix. The results of this work showed that in situ Si3N4/MoSi2 composite powder prepared by combustion synthesis could be successfully pressureless sintered and significant improvement of mechanical properties could be achieved.
Authors: Shoichi Kume, Saruhan Saklar, Koji Watari
Abstract: Attempts have been made to sinter hexagonal boron nitride (h-BN) by pressureless-sintering in air. In order to achieve this purpose, feldspar has been selected as a sintering aid to produce sintered compacts at a temperature above the melting point of feldspar. Even though h-BN was not wetted by the molten feldspar in nitrogen, the wettability was significantly improved in air. Through the heating process, the h-BN powder disappeared owing to the oxidation of the powder followed by sublimation of the boron oxide. The decomposition of BN was prevented effectively by the presence of molten feldspar in the h-BN/feldspar (30 vol.%) compact. It was shown that h-BN/feldspar composite can be sintered in air under normal pressure, although the bulk density of h-BN/feldspar composites (1.40 to 1.51 g/cm3) was not satisfactory enough.
Authors: Wynette Redington, J. Lonergan, G. Le Gonidec, A. Díaz, H. Bilgen, Stuart Hampshire
Authors: Wen Song Lin, Liang He
Abstract: Ceramics composites of B4C matrix with 5 wt% Al and various amount of ZrO2 additives were pressureless sintered under vacuum at 2250 °C for 60 min. Density, hardness, flexural strength and microstructure of the specimens were measured and characterized. Densities above 97% theoretical density (TD) were determined in the samples prepared with the addition of 8 wt% ZrO2 and 5 wt% Al, compared to 86% TD for single-phase B4C. X-ray diffraction analysis showed that B2O3 (impurity in B4C) was eliminated and new phases (ZrB2 and B4C1-x) were formed in the sintered samples, suggesting that in situ reactions between B4C/B2O3 and Al/ZrO2 happened during sintering process. It was showed that the elimination of B2O3 and the forming of boron rich solution of B4C1-x significantly improved the sinterability of B4C matrix ceramics, and consequently enhanced the densification rate greatly. The flexural strength and Vickers hardness of the sintered samples with addition of 8 wt% ZrO2 and 5 wt% Aluminum reached the value of 560 MPa and 30.2 GPa respectively, much higher than those of single-phase B4C ceramics.
Authors: Yong Feng Li, Ping Liu, Xiang Dong Wang, Hai Yun Jin, Guan Jun Qiao
Abstract: Porous silicon nitride ceramics with various amounts (25, 35, and 45 vol %) of hexagonal boron nitride (h-BN) were fabricated at 1800°C for 2h by the pressureless sintering process. With FESEM and TEM, the effects of h-BN on the microstructure and mechanical properties of Si3N4 ceramics were investigated. Results of the microstructure and mechanical properties of Si3N4/BN composites showed that the growth of the elongated β-Si3N4 were hindered by h-BN additive, which resulted in the decrease of fracture toughness of Si3N4/BN ceramics with increasing h-BN content. The morphologies of the fracture surfaces by FESEM revealed the fracture mode for Si3N4/BN composites to be intergranular. However, phase analysis by XRD indicated that the effect of h-BN on the α- to β- Si3N4 phase transformation of Si3N4/BN composites was negligible.
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