Papers by Keyword: Ceramic

Abstract: A simple and new method was introduced to measure the elastic modulus and strength of glass and brittle ceramic materials at different temperatures by compressing a notch ring specimen. For a notch ring specimen, the maximum tensile stress is generated in the outside of the testing sample at half of the height under an applied load. During the elastic deformation range, the elastic modulus can be calculated from the slope of loading curve and sample size. The fractured strength is derived by the critical load when the testing sample is failed. To verify the feasibility and reliability of this suggested method, typical brittle materials, including glass, coarse Al2O3 and fine ZrO2 ceramic, were used as the testing samples. The measured elastic modulus and strength obtained from this method at room temperature to 1300 oC agreed well with those from conventional testing methods.

Abstract: A study of the fracture phenomenon of zirconia-toughened alumina (ZTA) ceramics was carried. It analyzes the mechanisms of crack propagation of ZTA ceramics, and constructs fracture experiments of ZTA ceramics, so the propagation behavior on fracture in ZTA ceramics was investigated according to the experiment. By contrast, intercrystalline fracture happed in V-shaped groove of ceramic specimen under normal load without ultrasonic vibration during ceramic fracture, and transcrystalline fracture happed in V-shaped groove of ceramic specimen under normal load with ultrasonic vibration during ceramic fracture. Furthermore, the loading force of ceramic specimen under normal load with ultrasonic vibration is smaller than that under normal load without ultrasonic vibration all other conditions being equal. The results of fracture experiment prove that ultrasonic vibration assisted is good for the fracture of ceramic specimen, and it also proves that ultrasonic vibration assisted grinding may raise the working efficiency and improve surface integrity of ceramics from the standpoint of the fracture.

Abstract: The mechanical model of stress field was established in grinding with/without ultrasonic vibration assistance, based on indentation fracture mechanics. Compared with the stress field in conventional grinding, the research has shown that the grinding stress field changes periodically with the vibration process of the moving grains in ultrasonic grinding. In a vibration cycle, the grains interfere with the workpiece within the time of T+Δt and cut off the material from the workpiece surface. Meantime, the large impact force between the grinding wheel and the workpiece results in stress field on the ground surface. In other period of vibration cycle, the grains are detached from the workpiece surface, and there exists no interaction between them. The grinding force disappears, so does the grinding stress field.

Abstract: Technology of NC-contour evolution ultrasonic assisted creep feed grinding (NC-CEUACFG) blade surface was put forward to solve the difficult problem of machining ceramic blade surface. The static load on the grinding wheel and the influence of the rigidity of the grinding wheel on the surface precision were studied combined with the movement analysis between the blade and grinding wheel in the process of NC-CEUACFG ceramic blade surface, and the physical model of static load may explain the decrease of grinding force and increase of the relative rigidity of the grinding wheel in NC-CEUACFG in theory. The primary experiment of NC-CEUACFG blade surface was carried out according to the experimental results of previous optimized process parameters, and the integral impeller was machined directly in the blank material of Al2O3 ceramic, which indicated the application prospect of such technology.

Abstract: The sintering behavior and microwave dielectric properties of the (Ca0.9375Sr0.0625)0.25(Li0.5Sm0.5)0.75TiO3 (CSLST) ceramics doped with different amounts of Li2O-B2O3-SiO2-CaO-Al2O3 (LBSCA) glass were investigated. The sintering temperature of the CSLST ceramics can be effectively reduced over 200oC due to the addition of LBSCA glass. For the 5 wt% LBSCA-doped CSLST ceramics, which are sintered at only 1000 oC for 5 h, show optimum microwave dielectric properties as follows: εr=84.74, Qf=2446 GHz and τf=-12.48 ppm/oC.

Abstract: Contact mechanics is widely used to explore the mechanical properties of brittle materials while it rules the mechanical performance of industrial pieces. Elastic, plastic and brittle responses can be investigated and are highlighted. The indentation plastic zone can be decomposed into a central highly strained zone and rosette arms. The evolution of the central zone extension can be predicted by Johnson’s cavity model obtained under full load while on the other hand rosette arm extension is to be modeled considering the residual stresses from the indentation. Upon a post heat treatment, further development is obtained both experimentally and theoretically. Using large loads, elimination of cracks can be achieved using higher temperature to pass the brittle-ductile transition.

Abstract: Metal matrix composites (MMCs) were produced by Ni-induced pressureless infiltration using Fe alloy. The mainly fabrication process was that Ni and Al2O3 powders mixture was pressed and sintered after milled, and then the sintered Al₂O₃ ceramics were infiltrated by Fe alloy at 1600°C with 4h holding time. While the SEM and EPMA analyses indicated that the interface between ceramics and Fe alloy reaches a full homogeneity after infiltration and Fe alloy could infiltrate Al₂O₃ ceramic preforms and the maximum infiltration distance was more than 400 μm. This would increase the strength of interfacial due to excellent bonding interface. The fracture strength is about 63.0 MPa.

Abstract: Steel conveying rollers used in hot rolling mills must be exchanged very frequently at great cost because hot conveyed strips induce wear on the surface of roller in short periods. In this study, new roller structure is considered which has a ceramics sleeve connected with two short steel shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide longer life and reduces the cost for the maintenance. However, sometimes the steel shaft has to be pulled out for exchange. Simply, heating outside surface and cooling inside surface of the shaft are necessary for separation. However, attention should be paid to the maximum thermal stress of the ceramics sleeve in the process of separation. In this paper, finite element method analysis is applied to the structure and thermal stress has been calculated with the varying dimensions of the structure. Also several effects on thermal stress have been investigated, such as the effect of shrink fitting ratio, outside diameter, the fitted length, thickness of shaft, materials an so on. Finally the most appropriate thermal conditions to reduce maximum stress and make separation easy have been discussed, which is very useful for designing of new rollers.

Abstract: A phase field model is used to describe the microstructural development during the ceramic sintering. The evolution of the density is governed by Cahn-Hilliard equation, while the long-range order (lro) parameter fields by the time-dependent Ginzburg-Landau equation. In the simulation, green microstructures that consist of circular particles with different particle-size distributions and green densities have been produced by the stochastic growth model. The porosity of 25.6% was considered. The formation and growth of sintering neck, the seal, spheroidization as well as disappearance of pores and growth of grains are observed during simulation. The simulation results show grain boundary diffusion and surface diffusion are the dominate mechanism at the initial sintering stage. The predicted growth exponent of sintering neck and grain is consistent with the existing theoretical analysis.

Abstract: Phenolic resin was used as the raw material, formed a mold for complex-shaped component by rapid-prototyping. It was composed of SiC, C and Si. The sample hardness was analyzed through statistical comparison. The phase composition of C/SiC composite was investigated by XRD and microstructures of C/SiC ceramic components were observed with scaning electron microscope. The ceramic components obtained at 1500 by reactive infiltration of Si into porous C-template. The porous structure formed by photecurable resin and starch powders pyrolysis could effectively prevent the C-template from cracking and reduce the stress. It also facilitate penetrating Si to the C-template to form SiC.