The application of c/c-Siccomposites remains a challenge because of the poor mechanical properties induced by the liquid silicon infiltration method. In this study, a thick high textured pyrolyticcarbon (HT Pyc) int...
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The application of c/c-Siccomposites remains a challenge because of the poor mechanical properties induced by the liquid silicon infiltration method. In this study, a thick high textured pyrolyticcarbon (HT Pyc) interface manufactured by chemical vapor infiltration (cVI) was used to protect the carbon fibers and improve the flexural properties. The microstructure of HT Pyc, its flexural properties, and its associated strengthening and toughening mechanisms were analyzed on the c/c-Siccomposites. The results showed that the bending strength of the c/cSiccomposites was 344.74 MPa, which is nearly 31.82% higher than that of c/ccomposites. The fracture mode transformed from brittle fracture to pseudoplastic fracture owing to the addition of Sic, and the c/c-Siccomposites maintained a better toughness compared to c/ccomposites. Multiple mechanisms of strength and toughness improvement were found to be responsible for the excellent performance of the c/c-Siccomposites. The HT Pyc interface played a critical role in the excellent flexural properties. The strong bonding among the carbon layers and high interfacial strength between the fiber and HT Pyc led to the increase of strength. Besides, the improvement in toughness was attributed to the multiple effects of the carbon-layers deformation, cracks deflection and propagation caused by the bridging areas, sublayers, nano-and micro-scale cracks.
Dependence of the combustion of a Ti + c granular charge on a granule size is experimentally studied. It is revealed that the burning rate of a granular mixture of all fractions used in the work is higher than the bur...
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Dependence of the combustion of a Ti + c granular charge on a granule size is experimentally studied. It is revealed that the burning rate of a granular mixture of all fractions used in the work is higher than the burning rate of a bulk-density powder mixture. It is shown that, with a decrease in the granule size, the burning rate of the charge in the absence of gas decreases due to an increase in the number of boundaries between the granules per unit length of the sample. A strong influence of the nitrogen flow on the burning rate of both coarse and fine granules is established. It is shown that, in contrast to fine granules, an increase in the nitrogen flow rate of coarse granules up to 600 liters/h leads to a transition to convective combustion. The studies performed indicate that, despite the structural analogy between mechanically activated and granular mixtures, the relationship between the combustion time and the front transition time in granular mixtures is completely different. This means that the combustion of granular mixtures even in the absence of a gas flow cannot be explained within the framework of a microheterogeneous model.
c/MgO composite powders were prepared by combustion synthesis using magnesium oxalate and magnesium powders as raw materials. The phase composition and microstructure of the composite powders were investigated by X-ra...
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c/MgO composite powders were prepared by combustion synthesis using magnesium oxalate and magnesium powders as raw materials. The phase composition and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy/energy dispersive spectroscopy (FESEM/EDS), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The synthetic mechanism was explored through TG-FTIR and combustion front quenching techniques. It was found that the c/MgO composite powders contained a large quantity of MgO nanofibers. When the molar ratio of magnesium oxalate and magnesium was 1:4, the carbon content of the product reached a maximum of 9.45 wt %. In the composite powders, cubic MgO particles were encapsulated by a thin carbon layer, and there was a tiny gap between MgO and the carbon layer;a large number of MgO nanofibers with aspect ratios of 80?100 were found. The cubic MgO particles of the products are the direct decomposition of Mgc2O4, and the MgO nanofibers are the reaction product of gaseous Mg and cO2/cO at high temperature. Meanwhile, the carbon deposited on the MgO particles can inhibit the grain growth of MgO particles and result in the refinement of MgO particles. The uniform dispersion of carbon and the weak c/MgO interface combine, making the composite powders a potential additive for low-carbon MgO?c refractories with excellent thermal shock resistance.
A progressive oxidative damage model of c/Siccomposites, which is based on the oxidation mechanism and mechanical model of c/Siccomposites, is presented to simulate the damage process of c/Siccomposite under stress...
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A progressive oxidative damage model of c/Siccomposites, which is based on the oxidation mechanism and mechanical model of c/Siccomposites, is presented to simulate the damage process of c/Siccomposite under stressed oxidation environments. Firstly, the oxidation failure time of fibers was calculated according to the fiber stress and the fiber strength decline rule under stressed oxidation environments. Secondly, the stress redistribution and crack propagation around fracture fibers were given by combining the fracture position of fibers with the mechanical model, and the crack propagation would cause more fibers to be oxidized. Thirdly, the progressive oxidative damage process of c/Siccomposites under stressed oxidation environments was simulated by repeating the cyclic process of fiber oxidation fracture and crack propagation around the fracture fibers. Finally, through the progressive oxidative damage model, the stress-strain curves and fracture morphology of the unidirectional c/Siccomposites after stressed oxidation were predicted. The simulation results were correlated well with the experimental results, in terms of stressed oxidation life, stress-strain curve and variation law of fracture morphology, which indicated the reliability of the model.
In order to study the effects of temperature on the material behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (c/c-Sic), the mechanical properties at room temperat...
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In order to study the effects of temperature on the material behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (c/c-Sic), the mechanical properties at room temperature (RT) in in-plane and out-of-plane directions are summarized and the tensile properties of c/c-Sic were then determined at high temperature (HT) 1200 degrees c and 1400 degrees c under quasi static and compliance loading. The stressstrain response of both HT tests is similar and almost no permanent strain can be observed compared to the RT, which can be explained through the relaxation of residual thermal stresses and the crack distribution under various states. The different fracture mechanisms are confirmed by the analysis of fracture surface. Furthermore, based on the analysis of hysteresis measurements at RT, a modeling approach for the prediction of material behavior at HT has been developed and a good agreement between test and modeling results can be observed.
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