To improve the oxidation-resistance properties,SiC and TaC species were introduced in C/C composites by chemical vapor infiltration(CVI) methods. The oxidation-resistance properties of C-SiC-TaC-C composites were stud...To improve the oxidation-resistance properties,SiC and TaC species were introduced in C/C composites by chemical vapor infiltration(CVI) methods. The oxidation-resistance properties of C-SiC-TaC-C composites were studied by X-Ray diffractometry(XRD),JEOL-6360LV scanning electronic microscopy(SEM) and AdventurerTM electronic balance with precision of 0.1 mg. The results show that,1) the oxidation rate of the composites increases continuously with time at all experimental temperatures;2) The oxidation rate increases with temperature within 700-1 100 ℃,slowly in 700-800 ℃,acutely in 800-1 100 ℃;it reaches a maximum value at 1 100 ℃,then decreases within 1 100-1 400 ℃;3) The relationship curve of oxidation rate with temperature can be divided into three regions. The oxidation rate is controlled by reactivity in region Ⅰ,the mixed effects of reactivity and gas diffusion in region Ⅱ,gas phase diffusion in region Ⅲ;4) The composites exhibit a higher oxidation onset temperature in low temperature region and a lower oxidation rate at high temperature due to the oxidation of TaC to(Ta,O) and the formation of the dense SiO2-Ta2O5 oxide layer respectively. With the addition of SiC/TaC species,the oxidation-resistant properties of C/C composites can be improved effectively.展开更多
Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the de...Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the deposition of tribological coatings. In this study, anti-corrosive and electrical conductive carbon-based coatings with a metallic interlayer were prepared on stainless steel substrates as surface modification for metallic bipolar plates. Hereby, the influence of the deposition temperature during the deposition of the carbon top layer was investigated. Raman spectroscopy revealed differences in the microstructure at 200°C compared to 300°C and 100°C. Measurements of the interfacial contact resistance showed that the deposited coatings significantly improve the electrical conductivity. There are only minor differences between the different carbon top layers. The corrosion resistance of the coatings was studied via potentiodynamic polarization at room temperature and 80°C. Experiments showed that the coating with a carbon top layer deposited at 200°C, considerably reduces the current density and thus corrosion of the substrate is suppressed.展开更多
Three different coatings, Cr, SiO2/Cr and HfO2/SiO2 were deposited by electron beam physical vapor deposition (EB-PVD). Relevant composition and mechanical properties were obtained. The results show that the surface m...Three different coatings, Cr, SiO2/Cr and HfO2/SiO2 were deposited by electron beam physical vapor deposition (EB-PVD). Relevant composition and mechanical properties were obtained. The results show that the surface mechanical property could be increased, and Cr coating sample possessed the highest microhardness. Cyclic oxidation in air at 773 K was applied to evaluate the oxidation resistance of the coatings, and the section morphologies of the coatings were observed by FEISEM. The results indicate that the oxidation rate of AZ31 with Cr, SiO2/Cr and HfO2/SiO2 coatings is decreased, and the SiO2/Cr coating sample exhibits the best oxidation resistance and keeps relatively good adhesion up to 96 h. Polarization results prove that the corrosion resistance of AZ31 can be improved and the SiO2/Cr coating sample has the best property.展开更多
碳化硅(SiC)电子器件的性能和成本受衬底质量影响,因此生长大直径高品质SiC单晶意义重大。物理气相传输(PVT)法是一种常用的生长方法,但其主要面临热场设计与气流控制问题。本工作对电阻加热PVT法生长150 mm SiC单晶完整过程开展数值仿...碳化硅(SiC)电子器件的性能和成本受衬底质量影响,因此生长大直径高品质SiC单晶意义重大。物理气相传输(PVT)法是一种常用的生长方法,但其主要面临热场设计与气流控制问题。本工作对电阻加热PVT法生长150 mm SiC单晶完整过程开展数值仿真研究,建立描述SiC原料热解和再结晶及其多孔结构演变、热-质输运、晶体形貌变化的数理模型,用数值模拟手段研究晶体生长、原料演变与热场变化等过程间的耦合关系。结果显示:原料区侧面高温导致气流不均匀,晶面呈“W”形,原料区底部高温得到均匀气流和微凸晶面;长晶界面通过径向温度变化调节气相组分平衡压力,使晶面生长成等温线形状;晶体生长速率与原料温度、剩余原料量呈正相关。模拟结果与已报道实验结果吻合,对优化生长SiC单晶有指导意义。展开更多
The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate ...The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate the friction and wear properties of the MoS_(2)bilayer at the nanoscale by applying a normal load ranging from 200 to 1,000 nN.Scratch resistance is measured using the scratch mode in FFM based on a linearly increasing load from 100 to 1,000 nN.Kelvin probe force microscopy(KPFM)is performed to locally measure the surface potential in the tested surface to qualitatively measure the wear/removal of Mos,layers and identify critical loads associated with the individual failures of the top and bottom layers.The analysis of the contact potential difference values as well as that of KPFM,friction,and height images show that the wear/removal of the top and bottom layers in the MoS_(2)bilayer system occurred consecutively.The FFM and KPFM results show that the top MoS_(2)layer begins to degrade at the end of the low friction stage,followed by the bottom layer,thereby resulting in a transitional friction stage owing to the direct contact between the diamond tip and SiO_(2)substrate.In the stable third stage,the transfer of lubricious MoS_(2)debris to the tip apex results in contact between the MoS_(2)-transferred tip and SiO_(2).Nanoscratch test results show two ranges of critical loads,which correspond to the sequential removal of the top and bottom layers.展开更多
基金National Natural Science Foundation of China(No.52161040)Major Science and Technology Research and Development Project of Jiangxi Province(No.20203ABC28W006)+1 种基金Natural Science Foundation of Jiangxi Province,China,(No.20202ACBL214011)Key Project of"Science and Technology to Promote Mongolian Development",China(No.XM2021BT03)。
基金Project (2006CB600908) supported by National Basic Research Program of China
文摘To improve the oxidation-resistance properties,SiC and TaC species were introduced in C/C composites by chemical vapor infiltration(CVI) methods. The oxidation-resistance properties of C-SiC-TaC-C composites were studied by X-Ray diffractometry(XRD),JEOL-6360LV scanning electronic microscopy(SEM) and AdventurerTM electronic balance with precision of 0.1 mg. The results show that,1) the oxidation rate of the composites increases continuously with time at all experimental temperatures;2) The oxidation rate increases with temperature within 700-1 100 ℃,slowly in 700-800 ℃,acutely in 800-1 100 ℃;it reaches a maximum value at 1 100 ℃,then decreases within 1 100-1 400 ℃;3) The relationship curve of oxidation rate with temperature can be divided into three regions. The oxidation rate is controlled by reactivity in region Ⅰ,the mixed effects of reactivity and gas diffusion in region Ⅱ,gas phase diffusion in region Ⅲ;4) The composites exhibit a higher oxidation onset temperature in low temperature region and a lower oxidation rate at high temperature due to the oxidation of TaC to(Ta,O) and the formation of the dense SiO2-Ta2O5 oxide layer respectively. With the addition of SiC/TaC species,the oxidation-resistant properties of C/C composites can be improved effectively.
文摘Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the deposition of tribological coatings. In this study, anti-corrosive and electrical conductive carbon-based coatings with a metallic interlayer were prepared on stainless steel substrates as surface modification for metallic bipolar plates. Hereby, the influence of the deposition temperature during the deposition of the carbon top layer was investigated. Raman spectroscopy revealed differences in the microstructure at 200°C compared to 300°C and 100°C. Measurements of the interfacial contact resistance showed that the deposited coatings significantly improve the electrical conductivity. There are only minor differences between the different carbon top layers. The corrosion resistance of the coatings was studied via potentiodynamic polarization at room temperature and 80°C. Experiments showed that the coating with a carbon top layer deposited at 200°C, considerably reduces the current density and thus corrosion of the substrate is suppressed.
文摘Three different coatings, Cr, SiO2/Cr and HfO2/SiO2 were deposited by electron beam physical vapor deposition (EB-PVD). Relevant composition and mechanical properties were obtained. The results show that the surface mechanical property could be increased, and Cr coating sample possessed the highest microhardness. Cyclic oxidation in air at 773 K was applied to evaluate the oxidation resistance of the coatings, and the section morphologies of the coatings were observed by FEISEM. The results indicate that the oxidation rate of AZ31 with Cr, SiO2/Cr and HfO2/SiO2 coatings is decreased, and the SiO2/Cr coating sample exhibits the best oxidation resistance and keeps relatively good adhesion up to 96 h. Polarization results prove that the corrosion resistance of AZ31 can be improved and the SiO2/Cr coating sample has the best property.
文摘碳化硅(SiC)电子器件的性能和成本受衬底质量影响,因此生长大直径高品质SiC单晶意义重大。物理气相传输(PVT)法是一种常用的生长方法,但其主要面临热场设计与气流控制问题。本工作对电阻加热PVT法生长150 mm SiC单晶完整过程开展数值仿真研究,建立描述SiC原料热解和再结晶及其多孔结构演变、热-质输运、晶体形貌变化的数理模型,用数值模拟手段研究晶体生长、原料演变与热场变化等过程间的耦合关系。结果显示:原料区侧面高温导致气流不均匀,晶面呈“W”形,原料区底部高温得到均匀气流和微凸晶面;长晶界面通过径向温度变化调节气相组分平衡压力,使晶面生长成等温线形状;晶体生长速率与原料温度、剩余原料量呈正相关。模拟结果与已报道实验结果吻合,对优化生长SiC单晶有指导意义。
基金This study was supported by the Research Program funded by the SeoulTech(Seoul National University of Science and Technology,Republic of Korea).
文摘The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate the friction and wear properties of the MoS_(2)bilayer at the nanoscale by applying a normal load ranging from 200 to 1,000 nN.Scratch resistance is measured using the scratch mode in FFM based on a linearly increasing load from 100 to 1,000 nN.Kelvin probe force microscopy(KPFM)is performed to locally measure the surface potential in the tested surface to qualitatively measure the wear/removal of Mos,layers and identify critical loads associated with the individual failures of the top and bottom layers.The analysis of the contact potential difference values as well as that of KPFM,friction,and height images show that the wear/removal of the top and bottom layers in the MoS_(2)bilayer system occurred consecutively.The FFM and KPFM results show that the top MoS_(2)layer begins to degrade at the end of the low friction stage,followed by the bottom layer,thereby resulting in a transitional friction stage owing to the direct contact between the diamond tip and SiO_(2)substrate.In the stable third stage,the transfer of lubricious MoS_(2)debris to the tip apex results in contact between the MoS_(2)-transferred tip and SiO_(2).Nanoscratch test results show two ranges of critical loads,which correspond to the sequential removal of the top and bottom layers.
