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Effect of Ar dilution flow rate on LPCVD a boron-doped carbon coating from BCl3-C3H6-H2-Ar mixtures
Yongsheng Liu,Litong Zhang,Laifei Cheng,Wenbin Yang,Yongdong Xu 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3
A boron-doped carbon coating was deposited from a BCl3-C3H6-H2-Ar system by LPCVD. The effects of the Ar dilution flow rate on deposition rates, morphologies, compositions and bonding states were investigated. Deposition rates were almost the same, about 250 nm/h with different Ar dilution flow rate. Surface morphologies were also almost the same. The flat conchoidal aspect of the fracture surface transformed to a laminated structure with an increase in the Ar dilution flow rate. The carbon concentration was above 76.3 at.%, and the boron concentration was less than 17.9 at.%. The boron concentration increased with an increase in the Ar dilution flow rate, corresponding to a decreasing carbon concentration. The main bonding state of boron was B-sub-C and BC2O. The whole deposition process was dominated by a PyC formation reaction, which led to almost the same deposition rate with different Ar dilution flow rates. A boron-doped carbon coating was deposited from a BCl3-C3H6-H2-Ar system by LPCVD. The effects of the Ar dilution flow rate on deposition rates, morphologies, compositions and bonding states were investigated. Deposition rates were almost the same, about 250 nm/h with different Ar dilution flow rate. Surface morphologies were also almost the same. The flat conchoidal aspect of the fracture surface transformed to a laminated structure with an increase in the Ar dilution flow rate. The carbon concentration was above 76.3 at.%, and the boron concentration was less than 17.9 at.%. The boron concentration increased with an increase in the Ar dilution flow rate, corresponding to a decreasing carbon concentration. The main bonding state of boron was B-sub-C and BC2O. The whole deposition process was dominated by a PyC formation reaction, which led to almost the same deposition rate with different Ar dilution flow rates.
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Fundamental issues of applications of C/SiC composites for re-entry vehicles
Yani Zhang,Litong Zhang,Hui Mei,Qingqing Ke,Yongdong Xu,Laifei Cheng 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3
Carbon fiber reinforced silicon carbide ceramic matrix composite materials (C/SiCs) are being tested for hot structures and thermal protection systems (TPS) of launch vehicles and spacecraft, and also for advanced friction system of aircraft and racing cars. A number of tribological and joining components are required in these applications, such as bushing and rolling contact bearings, nuts and bolts, which require excellent mechanical, physical and chemical properties at temperatures higher than 1650℃. This study summarizes preparation of C/SiC load-carrying bearings for hinge by the Chemical Vapor Infiltration (CVI) method and C/SiC bolts for joints by the CVI + PIP (Polymer Impregnation and Pyrolysis) methods. The hinge bearing and bolts were examined in a simulated re-entry environment. Stress-oxidation was investigated under different stress levels from 0 to 200MPa up to 1800℃. The friction behavior of the hinge bearing system was studied under high loads (up to 25 kN) and low rotating velocities. The mechanical properties of the bolts with a thread connection were conducted under tensile and shear fatigue at both room temperature and elevated temperature. The results show that the stress-oxidation behavior of 2D-C/SiC composites in a combustion environment is a combined effect of extremely high load, high temperature, and oxidation. The load and temperature influenced the crack openings and thus the oxidation of carbon fibers in the precracked composites. The combustion environment mainly determined the time to failure of the specimens by oxidation damage under a high applied stress. Reliable thermal load-carrying ability and stable friction performance of the hinge bearing is demonstrated in high-temperature combustion environments with extremely high loads. The oxidation products of SiO2 at high temperatures between surfaces played an important role to modifies the friction by providing a protective layer. The room temperature tensile and shear strength of the bolts made of needled C/SiC are 139 MPa and 83 MPa, respectively. Even at 1800℃ in a combustion environment, the strengths still retained about 116MPa with a maximum decrease of 13%. More importantly, the bolts did not suffer significant mechanical degradation after tension-tension fatigue at 1 Hz for 24 h. Carbon fiber reinforced silicon carbide ceramic matrix composite materials (C/SiCs) are being tested for hot structures and thermal protection systems (TPS) of launch vehicles and spacecraft, and also for advanced friction system of aircraft and racing cars. A number of tribological and joining components are required in these applications, such as bushing and rolling contact bearings, nuts and bolts, which require excellent mechanical, physical and chemical properties at temperatures higher than 1650℃. This study summarizes preparation of C/SiC load-carrying bearings for hinge by the Chemical Vapor Infiltration (CVI) method and C/SiC bolts for joints by the CVI + PIP (Polymer Impregnation and Pyrolysis) methods. The hinge bearing and bolts were examined in a simulated re-entry environment. Stress-oxidation was investigated under different stress levels from 0 to 200MPa up to 1800℃. The friction behavior of the hinge bearing system was studied under high loads (up to 25 kN) and low rotating velocities. The mechanical properties of the bolts with a thread connection were conducted under tensile and shear fatigue at both room temperature and elevated temperature. The results show that the stress-oxidation behavior of 2D-C/SiC composites in a combustion environment is a combined effect of extremely high load, high temperature, and oxidation. The load and temperature influenced the crack openings and thus the oxidation of carbon fibers in the precracked composites. The combustion environment mainly determined the time to failure of the specimens by oxidation damage under a high applied stress. Reliable thermal load-carrying ability and stable friction performance of the hinge bearing is demonstrated in high-temperature combustion environments with extremely high loads. The oxidation products of SiO2 at high temperatures between surfaces played an important role to modifies the friction by providing a protective layer. The room temperature tensile and shear strength of the bolts made of needled C/SiC are 139 MPa and 83 MPa, respectively. Even at 1800℃ in a combustion environment, the strengths still retained about 116MPa with a maximum decrease of 13%. More importantly, the bolts did not suffer significant mechanical degradation after tension-tension fatigue at 1 Hz for 24 h.
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