Mechanics, Solid State and Engineering Materials

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Authors: Yu Сhao Li, Xiang Сai Ge, Sie Chin Tjong
Abstract: Binary poly(vinylidene fluoride)/silicon carbide (PVDF/SiC) composites and its graphite nanosheets (GN) doped ternary hybrids were fabricated using simple solution mixing and hot compression molding process. The dielectric behavior of such hybrids was studied over a wide frequency range. Additions of graphite nanosheets with their concentrations close to the percolation threshold were found to be very effective to enhance the dielectric permittivity of PVDF/SiC system. The dielectric constant for PVDF/SiC/GN 80/20/2 system was ~ 200, being twenty times higher than that of neat PVDF. Furthermore, the dielectric behavior of such hybrid displayed strong frequency dependence.
Authors: Ze Bao Lang, Xu Hu Zhang, Liang Wang, Wen Jun Jia
Abstract: After treated with different quenching processes near transition temperature of orthorhombic phase, PM Ti-23Al-17Nb alloys with different microstructures were obtained. Microstructures of the alloy were observed by optical microscope, and tensile properties were also tested. In order to analyze the relationship between microstructures and tensile properties at room temperature, fractures of broken test bars obtained in tensile tests were characterized by SEM. The results show that quenching process below transition temperature of orthorhombic phase has few effects on improvement of size and morphology of crystal grain. However, it may lead to an abnormal growth of partial crystal grain, which results in low tensile strength and poor ductility; Quenching process above transition temperature of orthorhombic phase can cause recrystallization of B2 phase, which make a remarkably improvement on size and morphology of crystal grain. Moreover, the alloy performs the max tensile strength of 1026 MPa and the max ductility of 5.8% after quenched at the temperature of 1020
Authors: Zhe Liu, Wei Ping Chen, Yu Deng
Abstract: Six groups of castings which solidified at different cooling rates with or without addition of 0.03%Sb were fabricated. The effects of the melt holding time, cooling rate, and Sb on the microstructure of ductile iron were studied. Results show that as for the other three blocks with addition of 0.03%Sb, reducing the length of eutectic plateau could improve the graphite morphology, and sufficient residual contents of spheroidizing elements REE and Magnesium could also lead to small and diffuse globular graphite particles no matter what the cooling rate is. As for the other three blocks with addition of 0.03%Sb, no matter what the cooling rate is, the nodularity index values are all about 90%. The main difference among the three blocks is just the size of nodular graphite. And even if two of the blocks solidified at different cooling rates, they own nearly identical NI value and globular graphite average diameter value, which is because they both possess the tolerated rare-earth elements/antimony ratio for spheroidal graphite formation.
Authors: Tong Kun Cao, Jun Peng Ge, Qi Long Yang
Abstract: Al2O3/TiC ceramic composites with the addition of CaF2 solid lubrication were produced by hot pressing. The effects of various conditions on tribological behaviors of Al2O3/TiC/CaF2 have been studied. The sliding wear tests against cemented carbide and 45 steel were performed on the ceramic composites using ring-block method. Results showed that with the increase of load and sliding speed, the friction coefficient decreased. However, the wear rate increased slightly with the increase of load and decreased with the increase of sliding speed. At low speed, the abrasion resistance of Al2O3/TiC/CaF2 coupled with cemented carbide was better than with 45 steel, while the abrasion resistance showed little difference at high speed. The friction coefficients were little different when coupled with cemented carbide and 45 steel respectively. During the sliding process, at the initial stage, the friction coefficient was waved because the self-lubricating film was not formed on the worn surface; after sliding 628m, the friction coefficient was stable because the self-lubricating film was formed on the worn surface.
Authors: Guang Ye Zhang, Dong Wen Ye, Jin Lin Wang, You Ming Chen, Long Fei Liu, Yuan Jun Guo
Abstract: The Microstructure and creep behavior for NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P alloy at high temperature have been investigated in this paper. The results reveal that the high temperature creep behavior of the NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P alloy is characterized by transient primary creep and dominant steady-state creep as well as ternary creep behavior. The primary creep can be described by Garofalo equation and the steady-state creep can be depicted by Dorn equation. The creep mechanisms are viscous glide of dislocations at lower and middle testing temperatures and dislocation climb at higher temperature. No change of the microstructure for the testing alloy indicates that the creep fracture is controlled by the formation and propagation of cavities and cracks, and the creep fracture behavior obeys Monk man-Grant relationship.
Authors: Yong Xu, Z.N. Guo, Guan Wang, Y.J. Zhang
Abstract: Resistance Spot Welding (RSW) is a widely used technology. And the rapid wear is the main reason for the short life of RSW electrodes. To improve electrode life during RSW, a novel ultrasonic-aided electro-spark deposition technology (UESD) and device are proposed in this paper. The WC metallurgical bond coating was fabricated on the surface of CuCr1 electrodes by UESD, and some experimental results were also analyzed. Moreover, the surface morphology of WC coating was studied by SEM and the quality of coating wear resistance was analyzed through experimental method. This study provides a novel way to extend the life of common moulds and RSW electrodes.
Authors: Jing Feng Guo, Ren Gen Xu, Li Zhao, Wen Zhu Shao, Lian Jie Qin
Abstract: Initiation and propagation of micro cracks in the Fe-25Cr-35Ni based superalloy were observed and investigated through in situ tensile test in SEM using a single-edge notched specimen. The results show that the micro crack sources may easily occur with one of those, the second phase particles and matrix interface, and the stress concentration region. The micro-cracks which propagated at first for those that are perpendicular to the tensile load would be growing up and connected mutual with the increase of external stress until forming the main crack. While the length of the mail crack enlarged enough in the specimen, it become instable for the main cracks and the fracture occurred rapidly.
Authors: Jian Peng, Chuan Bin Wang, Ling Li, Qiang Shen, Lian Meng Zhang
Abstract: Arc-melting was employed to synthesize BaTi2O5 powders by fast melting the reagent mixture of BaCO3 and TiO2 with different molar ratios (0.90~1.05:2). The influence of molar ratios of BaCO3 to TiO2 on the phase of the powders derived from arc-melting was investigated by X-ray diffraction and Raman spectra. When the molar ratio was larger than 0.95:2, a little amount of Ba-rich compound Ba2TiO4 was produced besides the main phase of BaTi2O5. Ti-rich compound Ba6Ti17O40, BaTi2O9 and TiO2 began to appear at the ratios ranging from 0.90:2 to 0.95:2. Single-phased BaTi2O5 powders were obtained by arc-melting the reagent mixture with the molar ratio of 0.95:2.
Authors: Yu Сhao Li, Xiang Сai Ge, Sie Chin Tjong
Abstract: The dielectric relaxation behavior of poly (vinylidene fluoride) based composites filled with beta silicon carbide nanoparticles were investigated over a wide frequency range and temperature intervals. The composites exhibited dielectric relaxations in the tested frequency range and the relaxations of composites can be well described via the modulus formalism of dielectric spectroscopy. Further, activation energy determined from the isothermal dielectric relaxations tended to decrease with increasing SiC indicating the promotion of SiC to the dipole relaxations of PVDF.

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