Key Engineering Materials Vols. 336-338

Abstract: The dry friction behaviors of reaction-bonded silicon carbide (RB-SiC) with different particle sizes were studied at high temperature using pin-on-dick friction testing method. The results showed that the friction coefficient of RB-SiC was the highest at 300°C, and lower at room temperature and 600°C, but the wear rate of RB-SiC would be increased with the increase of temperature. The XRD analysis of grits showed that there was only the amorphous silica in grits at room temperature, whereas the amorphous and crystal silica combined in grits tested at 600 °C. The wear mechanisms of RB-SiC at room temperature and elevated temperature were analyzed by of scanning electron microscopy (SEM) observation on worn surface morphology of RB-SiC.

Abstract: Ceramic microbeads are increasingly being used for wear applications, especially for milling ultrafine powder. Research on friction and wear behavior of ceramics has become a more and more important subject in the area. In this paper, three kinds of ceramic microbeads ––mullite-zirconia, zirconium silicate and 95 alumina microbeads which were produced by Colloidal injection moulding technique were tested by SRV high temperature friction and wear test system, which the working condition of the ceramic microbeads as grinding media can be simulated to a certainty. The tests were done under dry friction and water lubrication respectively. Then their worn surfaces were observed using scanning electron microscopy. Through these experiments, the tribological properties and wear mechanisms of the self-wearing ceramic microbeads were investigated.

Abstract: The effects of rare earth oxides (Lu2O3 and La2O3) on the property, microstructure and oxidation behavior of hot-pressing sintered Si3N4 ceramics were investigated. The silicon nitride ceramics with Lu2O3 and La2O3 as addition have been fabricated by hot-pressed at 1800°C for 1h under a pressure of 25MPa. Oxidation test was carried out at 1400°C in air for 100 hours. Mechanical properties, SEM and XRD were measured before and after oxidation. The results showed that Si3N4 ceramics doped Lu2O3 had good microstructure and mechanical properties than those doped La2O3. Oxidation test showed a parabolic weight gain with oxidation time at 1400°C in air and the oxidation products of the ceramics were SiO2, Re2Si2O7 and Re2SiO5 confirmed by XRD and EDS. The rate-controlling step was the diffusion of ion. The samples doped Lu2O3 showed superior oxidation resistance to those doped La2O3.

Abstract: Compound ceramic coatings with the main crystalline of Al2TiO5 (as-coated samples) were prepared on Ti-6Al-4V alloy by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The coated samples were calcined in Ar and air at 1000oC, respectively. The phase composition, morphology and element content of the coatings were investigated by XRD, SEM and XRF. The samples treated in Ar and the as-coated ones were calcined in air at 1000oC to study the oxidation resistance of the samples. The results showed that Al2TiO5 decomposed and transformed into corundum and rutile TiO2 during the high temperature calcination. Al2TiO5 decomposed very quickly in air and the proportion of Al2O3 to TiO2 was 44:55 after a complete decomposition. On the contrary, Al2TiO5 decomposed very slowly in argon with the final proportion of Al2O3 to TiO2 of 81:18 on the coating surface. The morphology of the ceramic coatings after the calcination was also different. The coatings calcined in argon were fined: the grains and pores were smaller than those of the coatings calcined in air. The weight gains of both coatings changed in the form of parabola law, and the weight gains of the coated samples treated in argon were comparatively lower than that of the as-coated samples. During the high temperature calcination, the samples treated in argon cannot distort easily, compared with the as-coated ones.

Abstract: Geometric design procedures for the cycloidal drive with ceramic ball meshing elements were introduced. Using the theory of conjugate surfaces, the equations of meshing of the cycloid drive and the cycloid raceway profiles were derived. Design examples were presented to demonstrate the design procedure and feasibility. The ceramic balls were used as the meshing elements. Prototype of this research was made and tested with satisfying results. The results of this work are suitable for computeraided design and manufacture of industrial applications.

Abstract: An optimum model for the compositional design of advanced ceramic composites is built based on the impact resistance. The relative impact modulus IM0 is defined as an index for the characterization of impact resistance of brittle ceramics. Computer aided optimum technique is used to get the optimum compositions of the material. Results show that the material can be expected to have the highest impact resistance which is nearly 86% higher than that of the pure alumina when the volume fraction of Al2O3, SiC and Ti(C,N) is 72.3%, 14.8% and 12.9%, respectively. An advanced SiC/Ti(C,N)/Al2O3 ceramic composite is then fabricated according to the optimum results. When used as cutting tools, its impact fracture resistance is approximately 71%-76% higher than that of the pure alumina ceramic in the machining of hardened carbon steel. The increment coincides well with that predicted directly from the optimum model. It suggests that the method is feasible in the design and fabrication of ceramic composites especially for machining application.

Abstract: A computation method for parallel simulations of ceramic grain growth at an atomic scale in a PC cluster is proposed, by combining the Message Passing Interface (MPI) with the serial simulation of grain growth. A parallel platform is constructed for the simulation of grain growth with program modules of grain assignments, grain growth, data exchanges and boundary settlements, which are coded with Microsoft Visual C++ 6.0 and MPICH. Quantitative results show that the computing speed of parallel simulations with this platform is obviously increased compared with that of serial simulations. Such a computing mode of grain growth is in good agreement with practical situations of ceramic grain growth.

Abstract: Quantitative evaluation of repairing effect of bone grafting material is one of the essential studying subjects. However, traditional evaluation methods are subjective and qualitative. In this paper, the region of new bone from a bone repairing biomaterial planted image is extracted based on color image segmentation and then statistically analyzed to evaluate the property of bone grafting material quantitatively. HSI color model, which corresponds with people’s vision system for color is used to achieve ideal segmental results and effective utilization of color information. The S and I variable are used as thresholding condition for image segmentation, thereby obtaining the area of new bone. The effect of BMP contained in BMP/α-TCP is estimated furthermore. Experimental results show that the composite BMP/α-TCP induce more bone than pure α-TCP in virtue of BMP. This study provides theoretical and experimental suggestions for clinical applications of BMP/α-TCP.

Abstract: A three-layer back-propagation neural network model based on the non-linear relationship between the size of the SrTiO3 nanocrystalline and the technology factors, such as reaction time, reaction temperature, raw material adding amount of NaOH and SrCl2, and the rate of TiCl4/Hl, was established. Moreover, in order to accelerate the converging rate and avoid the non-converging situation, the momentum terms are introduced. Besides, the variable learning speed is adopted. At the same time, the input variables were pretreated by using the main component analysis firstly. And the results show that the improved back-propagation neural network model is very efficient for predication of the SrTiO3 nanocrystalline size.

Abstract: Finite element method (FEM) was used for planar ablation problem of heat protection materials based on thermal analysis. ANSYS, a commercial FEM code, was employed for modeling and calculating, and material deleting and boundary moving problems were solved with its advanced techniques. Various heat flux (HF) densities ranging from 1 to 10 MW/m2 as thermal loads were investigated to the effects of heat conduction and ablation, respectively. The results showed that a sudden thermal load can cause great temperature rise and high thermal gradient near the surface of the material. The ablative quantity and ablation rate were also calculated, and mathematical models have been deduced for them.