A Mo-Si-C-N multi-layered anti-oxidation coating was in-situ fabricated by introducing nitrogen atmosphere during the fused sintering of Mo-Si slurry pre-layer on carbon/carbon composites. The phase composition and mi...A Mo-Si-C-N multi-layered anti-oxidation coating was in-situ fabricated by introducing nitrogen atmosphere during the fused sintering of Mo-Si slurry pre-layer on carbon/carbon composites. The phase composition and microstructure of the Mo-Si-C-N coating were characterized by X-ray diffractometry, optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The Mo-Si-C-N coating exhibited a three-layered structure. Besides the MoSi2/Si main-layer and the SiC bonding-layer, a surface layer of about 10 μm in thickness was synthesized on the coating surface. The surface layer mainly consisted of SiC nanowires and contained some Si3N4 and Si phases. SiC nanowires of 10 to 200 nm in diameter presented a terrace and distortion structure. Transmission electron microscopy indicated that the SiC nanowires grew along the preferred 〈111〉 direction. During oxidation test, SiC nanowires transmuted into SiO2 glass, which can play an important role in improving the oxidation resistance of C/C composites.展开更多
Charring composites are widely used in the thermal protection system(TPS) to consume the intense aerodynamic heating during vehicle reentry. The ablation and thermal responses for the charring composites can be studie...Charring composites are widely used in the thermal protection system(TPS) to consume the intense aerodynamic heating during vehicle reentry. The ablation and thermal responses for the charring composites can be studied by using a numerical ablation model, in which the surface ablation and volume ablation could be taken into account. The coupling interactions among temperature, gas motion and interior pressure producing the pyrolysis gas could make the computation more complicated. A multi-physics model is developed to simulate the thermal response coupled with volume ablation and surface ablation. After studying four typical ablation cases, the model is validated, and then the heat transfer mechanisms in ablation are investigated. It is found that the viscous dissipation energy by the motion of pyrolysis gas can be neglected in the simulation. Also, the flow of pyrolysis gas plays an important role in the temperature response, especially under high heat flux condition.展开更多
It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications.The plasma wind tunnel ablation tests with high-entropy air and CO2 atmosp...It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications.The plasma wind tunnel ablation tests with high-entropy air and CO2 atmospheres,and compressive experiments in the ambient and 150℃,were conducted for three kinds of PICA-like materials(CF/PR-Si,CBCF/PR-SiOC and NQF/PR-Si composites).The traditional carbon/phenolic(C/PR)braided composites were also used for comparison.PICA-like materials have the better thermal insulation than traditional C/PR composite,especially for CBCF/PR-SiOC composite.The ablation behavior of CF/PR-Si and CBCF/PR-SiOC PICA-like materials in the CO2 atmosphere can produce a large amount of SiO2 in the form of coatings,oxide layers and skeletons on the ablated surface,which are greatly different from that in the air atmosphere.The compressive behavior of PICA-like material is greatly depended on the fiber fabrics,and exhibits the large discrete characteristics.The longer fiber in the PICA-like materials plays the role in maintaining the material integrity,while it may increase the thermal conductivity.展开更多
Ultra-high temperature ceramic(UHTC) composites are widely used in high-temperature environments in aerospace applications. They experience extremely complex environmental conditions during service, including thermal,...Ultra-high temperature ceramic(UHTC) composites are widely used in high-temperature environments in aerospace applications. They experience extremely complex environmental conditions during service, including thermal, mechanical and chemical loading. Therefore, it is critical to evaluate the mechanical properties of UHTCs subject to an environment with elevated temperature, mechanical stress and oxygen. In this paper, an experimental investigation of the uniaxial tensile properties of a ZrB_2-SiC-graphite subject to an environment with a simultaneously elevated temperature, mechanical stress and oxygen is conducted based on a high-temperature mechanical testing system. To improve efficiency, an orthogonal experimental design is used. It is suggested that the temperature has the most important effect on the properties, and the oxidation time and stress have an almost equal effect. Finally, the fracture morphology is characterized using scanning electron microscopy(SEM), and the mechanism is investigated. It was concluded that the main fracture mode involved graphite flakes pulling out of the matrix and crystalline fracture, which indicates the presence of a weak interface in the composites.展开更多
Materials chemomechanics is an exciting and fast growing field where mechanics meets chemistry, and has drawn increasing attention in recent years. It is concerned with the phenomena and mechanisms of coupled chemical...Materials chemomechanics is an exciting and fast growing field where mechanics meets chemistry, and has drawn increasing attention in recent years. It is concerned with the phenomena and mechanisms of coupled chemical and mechanical interactions. Chemomechanical coupling phenomena exist in many research areas, ranging from the development of advanced batteries, biomechanical engineering, hydrogen embrittlement, and high temperature oxidation. In fact, a typical chemomechanical problem usually involves the processes of diffusion, chemical reaction, deformation and stress generation. Such a strong coupling between chemistry and mechanics can give rise to the complex spatial-temporal evolution of composition, microstructure and morphology in materials.展开更多
基金supported by the Foundation of Heilongjiang Province (No. LC04C16)the Foundation of Aerospace Technology (No. HTJSZC-0506) the Post-Doctor Foundation of Heilongjiang Province, China
文摘A Mo-Si-C-N multi-layered anti-oxidation coating was in-situ fabricated by introducing nitrogen atmosphere during the fused sintering of Mo-Si slurry pre-layer on carbon/carbon composites. The phase composition and microstructure of the Mo-Si-C-N coating were characterized by X-ray diffractometry, optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The Mo-Si-C-N coating exhibited a three-layered structure. Besides the MoSi2/Si main-layer and the SiC bonding-layer, a surface layer of about 10 μm in thickness was synthesized on the coating surface. The surface layer mainly consisted of SiC nanowires and contained some Si3N4 and Si phases. SiC nanowires of 10 to 200 nm in diameter presented a terrace and distortion structure. Transmission electron microscopy indicated that the SiC nanowires grew along the preferred 〈111〉 direction. During oxidation test, SiC nanowires transmuted into SiO2 glass, which can play an important role in improving the oxidation resistance of C/C composites.
基金supported by the National Natural Science Foundation of China(Grant Nos.11672089&11732002)the Natural Science Foundation of Heilongjiang Province,China(Grant No.A2017003)the Fundamental Research Funds for the Central Universities(Grant No.HIT.NSRIF.2017017)
文摘Charring composites are widely used in the thermal protection system(TPS) to consume the intense aerodynamic heating during vehicle reentry. The ablation and thermal responses for the charring composites can be studied by using a numerical ablation model, in which the surface ablation and volume ablation could be taken into account. The coupling interactions among temperature, gas motion and interior pressure producing the pyrolysis gas could make the computation more complicated. A multi-physics model is developed to simulate the thermal response coupled with volume ablation and surface ablation. After studying four typical ablation cases, the model is validated, and then the heat transfer mechanisms in ablation are investigated. It is found that the viscous dissipation energy by the motion of pyrolysis gas can be neglected in the simulation. Also, the flow of pyrolysis gas plays an important role in the temperature response, especially under high heat flux condition.
基金supported by the National Natural Science Foundation of China(Grant Nos.11672089,11732002&11902333)。
文摘It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications.The plasma wind tunnel ablation tests with high-entropy air and CO2 atmospheres,and compressive experiments in the ambient and 150℃,were conducted for three kinds of PICA-like materials(CF/PR-Si,CBCF/PR-SiOC and NQF/PR-Si composites).The traditional carbon/phenolic(C/PR)braided composites were also used for comparison.PICA-like materials have the better thermal insulation than traditional C/PR composite,especially for CBCF/PR-SiOC composite.The ablation behavior of CF/PR-Si and CBCF/PR-SiOC PICA-like materials in the CO2 atmosphere can produce a large amount of SiO2 in the form of coatings,oxide layers and skeletons on the ablated surface,which are greatly different from that in the air atmosphere.The compressive behavior of PICA-like material is greatly depended on the fiber fabrics,and exhibits the large discrete characteristics.The longer fiber in the PICA-like materials plays the role in maintaining the material integrity,while it may increase the thermal conductivity.
基金supported by the National Natural Science Foundation of China(Grant Nos.11472092,11672088,11502058)the National Basic Research Program of China(Grant No.2015CB655200)
文摘Ultra-high temperature ceramic(UHTC) composites are widely used in high-temperature environments in aerospace applications. They experience extremely complex environmental conditions during service, including thermal, mechanical and chemical loading. Therefore, it is critical to evaluate the mechanical properties of UHTCs subject to an environment with elevated temperature, mechanical stress and oxygen. In this paper, an experimental investigation of the uniaxial tensile properties of a ZrB_2-SiC-graphite subject to an environment with a simultaneously elevated temperature, mechanical stress and oxygen is conducted based on a high-temperature mechanical testing system. To improve efficiency, an orthogonal experimental design is used. It is suggested that the temperature has the most important effect on the properties, and the oxidation time and stress have an almost equal effect. Finally, the fracture morphology is characterized using scanning electron microscopy(SEM), and the mechanism is investigated. It was concluded that the main fracture mode involved graphite flakes pulling out of the matrix and crystalline fracture, which indicates the presence of a weak interface in the composites.
文摘Materials chemomechanics is an exciting and fast growing field where mechanics meets chemistry, and has drawn increasing attention in recent years. It is concerned with the phenomena and mechanisms of coupled chemical and mechanical interactions. Chemomechanical coupling phenomena exist in many research areas, ranging from the development of advanced batteries, biomechanical engineering, hydrogen embrittlement, and high temperature oxidation. In fact, a typical chemomechanical problem usually involves the processes of diffusion, chemical reaction, deformation and stress generation. Such a strong coupling between chemistry and mechanics can give rise to the complex spatial-temporal evolution of composition, microstructure and morphology in materials.
