M Reece Pengarang B Vaidhyanathan Pengarang

Creep-rupture behaviour of notched oxide/oxide ceramic matrix composite in combustion environment Abhendra K. Singh, Volodymyr Sabelkin and Shankar Mall Department of Aeronautics and Astronautics, Air Force Institute of Technology, WPAFB, OH, USA ABSTRACT Creep-rupture tests were performed in the combustion environment on double-edge notch and centre hole oxide/oxide ceramic matrix composite specimens. The specimens were exposed to the maximum temperature of 1250 ± 50°C in the notch region where the combustion flame directly impinged. Specimens were loaded to the desired creep load levels and the loads were sustained till either the specimens ruptured or a run-out time of 25 h was achieved. Optical and scanning electron microscopes were used to characterise specimen damage. The test results were compared to its counterparts in 1200°C (isothermal) laboratory air environment. At a given creep life, the applied creep stress for both the notch types was generally lower in the combustion environment than the laboratory air environment. Finite element simulations attributed lower applied creep stress in the combustion environment to the presence of thermal gradient stresses, which were not present in the isothermal laboratory air environment. KEYWORD S Ceramic matrix composite; oxide/oxide; combustion; creep; fibre; matrix; rupture; thermal gradient stress Damage development and lifetime prediction of cross-ply ceramic-matrix composites subjected to cyclic loading at room and elevated temperatures Li Longbiao College of Civil Aviation, Nanjing University of Aeronautics and Astronautics, Nanjing, PR China ABSTRACT In this paper, the damage development and lifetime prediction of fibre-reinforced ceramicmatrix composites subjected to cyclic loading at elevated temperatures in oxidising atmosphere have been investigated. Considering the damage mechanisms of matrix cracking, interface debonding, interface wear and interface oxidation, the damage evolution of fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain, interface shear stress and broken fibres fraction have been analysed. The relationships between damage parameters and internal damage of matrix cracking, interface debonding and slipping, and fibres fracture have been established. The experimental fatigue hysteresis, interface slip lengths, peak strain, and the fatigue life curves of cross-ply CMCs under cyclic loading at elevated temperature have been predicted. The different fatigue behaviour in unidirectional and cross-ply CMCs at room and elevated temperatures subjected to low-cycle and high-cycle fatigue has been discussed. KEYWORD S Ceramic-matrix composites; airworthiness; damage evolution; oxidation; matrix multicracking; interface debonding Effect of calcining temperature on the microstructure and magnetic properties of CuFeO2 multiferroic ceramic Xinyu Xie, Haiyang Dai, Tao Li, Gaoshang Gong and Zhenping Chen School of Physics and Electronic Engineering, Zhengzhou University of Light Industry, 5 Dongfeng Rd, Zhengzhou 450002, China ABSTRACT Multiferroic ceramic CuFeO2 has been successfully fabricated by traditional solid-state reaction method under different calcining temperatures. X-ray powder diffraction results show that a higher calcining temperature is beneficial to form single delafossite phase with a hexahedron crystal structure. Raman and scanning electron microscopy results indicate that the proper calcining temperature is favourable to enhance the polarisation strength, grain size and density of samples. Magnetic properties results reveal that all samples exhibit two successive magnetic transitions with decreasing temperature, the corresponding magnetic transition temperature TN1 and TN2 are independent on calcining temperature. It is also found that the magnetic state of all samples at T= 10 and 13 K is weak ferromagnetic or ferrimagnetic state but not the antiferromagnetic state in theory. The value of magnetic susceptibility and saturation magnetisation are effectively enhanced by changing calcining temperature. The relationship between the microstructure and magnetic properties of CuFeO2 system is discussed in this paper. KEYWORD S CuFeO2 ceramics; calcining temperatures; microstructure; magnetic properties Elasto-optic behaviour in epitaxial films of perovskite oxide ferroelectrics Alexandr Dejnekaa and Marina Tyuninaa,b aInstitute of Physics, Academy of Sciences of the Czech Republic, Czech Republic; bFaculty of Information Technology and Electrical Engineering, Microelectronics Research Unit, University of Oulu, Oulu, Finland ABSTRACT Large variations of refractive index in the visible spectral range are obtained in epitaxial perovskite oxide ferroelectric films experiencing lattice strain. The strain is imposed by substrates, on top of which the films are grown. The optical constants are determined using the spectroscopic ellipsometry. As a reference and for comparison, also prototype single crystals are inspected. The variations in refraction are related to the lattice strain in the films. Elasto-optic coefficient is formally estimated using the out-of-plane lattice elongation or shrinkage in the films compared to bulk. The obtained elasto-optic coefficients exceed significantly those previously reported for ferroelectric materials. KEYWORD S Epitaxial films; elasto-optic; perovskites; refractive index Preparation of Al2O3–SiC composite powder from kyanite tailings via carbothermal reduction process Xin Min, Minghao Fang, Zhaohui Huang, Jiasheng Chen*, Jundong Zhang, Yan’gai Liu and Xiaowen Wu Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences (Beijing), Beijing, China ABSTRACT Al2O3–SiC composite powders were prepared from kyanite tailings mixed with 20% excess carbon coke via carbothermal reduction (CR) reaction. The optimised synthesis condition for synthesising Al2O3–SiC composite powders was at 1600°C for 6h. The equilibrium relationship curves of the condensed phases were presented and the temperature dependence of the phase composition was also studied. The results show that irregular Al2O3 and SiC grains first formed at 1500°C, and the elements C, O, Al, and Si randomly distributed in the each crystal particles. The amount of Al2O3–SiC composites increased with the increasing synthesis temperature and reaction time. Finally, Al2O3–SiC composite bulk materials were further prepared by pressureless sintering using the synthesised Al2O3–SiC composite powders as raw materials, and their mechanical properties were investigated in detail. All these results indicate that the CR method can offer a niche application for the development of kyanite tailings. KEYWORD S Kyanite tailings; carbothermal reduction; Al2O3; SiC Structural and functional characterisation of KNNS– BNKZ lead-free piezo ceramics J. Tangsritrakul and D. A. Hall School of Materials, University of Manchester, Manchester, UK ABSTRACT Promising piezoelectric properties have been reported recently for lead-free 0.96(K0.48Na0.52Nb0.95Sb0.05)–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS–BNKZ) ceramics. The presence of coexisting rhombohedral and tetragonal phases is thought to play a key role in their functional properties, but a thorough understanding is currently lacking. In this experiment, (1 −x)KNNS–(x)BNKZ ceramics with x = 0–0.05 were prepared by the mixed-oxide method. High-resolution synchrotron X-ray powder diffraction (SXPD) measurements reveal that the addition of BNKZ into KNNS ceramics leads to an increase in the rhombohedral–orthorhombic phase transition temperature (TR−O) and a decrease in the orthorhombic–tetragonal phase transition temperature (TO−T) leading to orthorhombic–tetragonal and rhombohedral–tetragonal phase coexistence at room temperature for compositions with x = 0.02 and 0.04, respectively. By combining the SXPD results with microstructure, evidence is also found for the occurrence of chemical heterogeneity, which could provide an additional means to control the functional properties. The structural observations are correlated with changes in the dielectric and ferroelectric properties. KEYWORD S Phase coexistence; lead-free; ferroelectric; synchrotron X-ray diffraction Synthesis and characterisation of self-assembled SiC nano wires and nano ribbons by using sol– gel carbo thermal reduction Yue Liu, Qiangang Fu, Hongjiao Lin, Beibei Wang and Lu Li State Key Laboratory of Solidification Processing, Carbon/Carbon Composites Research Center, Northwestern Polytechnical University, Xi’ an, Shaanxi, PR China ABSTRACT Hexagonal-shaped 3C-SiC nanowires were grafted onto SiC nanoribbons by a sol– gel technique using ferrocene as catalyst. The nanowire diameter ( ∼ 200 nm) and the nanoribbon width– thickness ratio (20:1) are uniform along their entire length. Their length is about several tens to several hundreds of micrometres. Meanwhile, single SiC nanostructure (nanowire or nanoribbon) was obtained by adjusting temperature field. A novel cooperative growth mechanism of vapour– liquid– solid and vapour– solid was proposed for the self-assembled SiC nanostructure. The self-assembled SiC nanowires and nanoribbons exhibit two strong broad photoluminescence peaks at wavelengths of about 373 and 471 nm, which are significantly shifted to the blue compared with the reported luminescence of SiC nanowires. This study will pave a way for the controllable synthesis of SiC nanowires and nanoribbons, and provide a simple method to connect them together firmly as potential applications for nanodevices in future. KEYWORD S Nanostructured materials; crystal growth; sol– gel processes; microstructure The cutting performance of Al2O3 and Si3N4 ceramic cutting tools in the milling plywood Xiaolei Guoa, Zhaolong Zhua, Mats Ekevadb, Xu Baoa and Pingxiang Caoa aFaculty of Material Science and Engineering, Nanjing Forestry University, Nanjing, China; bDivision of Wood Science and Engineering, Luleå University of Technology, Skellefteå, Sweden ABSTRACT This research focuses on the cutting performance of Al2O3 and Si3N4 ceramic cutting tools in upmilling plywood, the results of which are as follows. First, whether the tool material is Al2O3 or Si3N4 ceramic, the cutting forces at low-speed cutting were less than those at high-speed cutting, and the machining quality at low-speed cutting was greater than that at high-speed cutting. Then, whether at low- or high-speed cutting, the cutting forces of Al2O3 cutting tools were higher than those of Si3N4 cutting tools, and the machining quality of plywood milled by Al2O3 ceramic cutting tools was poorer than that milled by Si3N4 ceramic cutting tools. Finally, Si3N4 ceramic cutting tools were more suitable to machine the wooden productions with much glue content than Al2O3 ceramic cutting tools for the better machined quality. KEYWORD S Al2O3 ceramic cutting tools; Si3N4 ceramic cutting tools; plywood; cutting forces; machining quality