SiC添加量对真空烧结SiC/Zr复合材料显微组织及性能的影响

以SiC粉和ZrH₂粉为原料,用真空烧结法制备SiC/Zr复合材料。研究了SiC添加量对SiC/Zr复合材料显微组织及性能的影响。结果表明:未添加SiC时,材料为致密的Zr金属烧结体,但材料硬度和耐腐蚀性能相对较差;添加SiC后,SiC与Zr发生界面反应生成ZrC和Zr₂Si,SiC和基体Zr通过界面层紧密结合,与未添加SiC的试样相比,材料的致密度有所下降,但硬度和耐腐蚀性能均得到提升;随着SiC添加量的增加,试样的生坯致密度和烧结致密度降低,而组织中的第二相增多,烧结试样的硬度值先增大后减小,其中含15%SiC的烧结试样硬度值最大,耐腐蚀性能随SiC添加量的增加而提高。      

3D-Cf/SiC复合材料的弯曲强度及热膨胀性能分析

采用料浆浸渗和CVI工艺制备了含有ZrB₂陶瓷颗粒的3D-C_f/SiC复合材料,对其进行弯曲强度和线热膨胀系数测试,通过扫描电镜观察复合材料的表面及断口形貌。结果表明,3D-C_f/SiC复合材料的弯曲强度为107.99 MPa,满足一般热防护材料的使用要求;其线热膨胀系数随温度变化的规律是由于碳纤维和SiC陶瓷基体之间线热膨胀系数的不匹配及热残余应力造成的。     

用CVI方法制备SiC_f/SiC复合材料的弯曲断裂强度

对Ｓａｔｉｎｅ、Ｐｌａｉｎ 两种编织方式和不同涂层的Ｈｉ－Ｎｉｃａｌｏｎ 纤维,采用气相浸渍（ＣＶＩ）工艺技术制备出纤维强化型ＳｉＣｆ／ＳｉＣ复合材料,获得其室温至１７７３Ｋ温度范围内３ 点弯曲实验断裂强度曲线。分析Ｓａｔｉｎｅ、Ｐｌａｉｎ 两种二维纺织方法以及纤维涂层（碳、ＢＮ）对ＳｉＣｆ／ＳｉＣ复合材料弯曲断裂强度的影响。结果表明,Ｓａｔｉｎｅ样品的平均断裂强度高于Ｐｌａｉｎ 样品。而纤维涂层虽然使ＳｉＣｆ／ＳｉＣ复合材料的断裂强度有不同程度的下降,但其宏观塑性（挠度）得到明显提高,而且ＢＮ 涂层还使其高温强度增加。热处理工艺对样品弯曲断裂强度影响的实验表明,随着热处理温度升高,材料强度下降,宏观塑性提高。     

加速器CT无损检测大尺寸C/SiC复合材料构件

针对回转体和扁平体结构的大尺寸C/SiC复合材料构件,设计了可表征缺陷检测分辨率的像质计,研究了射线能量、准直器宽度等因素对不同类型构件检测结果的影响情况。结果表明:射线能量、准直器宽度及构件尺寸、形状等因素决定了构件内部缺陷检测分辨率;准直器的选择取决于构件的尺寸、形状等特征;射线能量的选择取决于构件的最大穿透厚度。     

利用脉冲中子伽马能谱判断岩性及影响因素的蒙特卡罗模拟

RPM(储层特性监测仪)能够在不同的时间内获取非弹性散射伽马能谱和热中子俘获伽马能谱,对谱数据进行处理获取C/O和地层的宏观吸收截面的同时,也可以利用得到的Si/O和Ca/O以及Si/Fe和Ca/Fe的交会图来判断岩性.通过蒙特卡罗方法模拟在套管井各种地层条件下的非弹和俘获能谱,研究利用交会图判断岩性,并给出饱和度、孔隙度、矿化度、井眼套管、持率、泥质含量等影响因素下的交会图,为利用RPM测井资料获取地层岩性信息及其影响因素提供了理论指导.     

贫化铀、贫化铀/氢化锂组合装置的泄漏中子能谱

建立了贫化铀和氢化锂球壳的聚变裂变混合能源堆的包层模拟装置.在PD300氘氚中子发生器直流运行模式下,用BC501A液体闪烁体探测器在0 °方向测量贫化铀和贫化铀/氢化锂球壳组合装置的DT中子轰击下的泄漏中子能谱(0.75-16 MeV),并用MCNP5程序和ENDF/B-VI数据库对装置进行模拟计算其泄漏中子能谱,两...     

炭/炭复合材料对活化片辐照的影响

根据钍基熔盐堆高温环境辐射测量需求,采用具有高温抗氧化Si C涂层的炭/炭复合材料作为待测活化片的载体材料,介绍了采用炭/炭复合材料作为辐照载体的优越性,对其进行了成分和热分析测试,并详细描述了带有炭/炭复合材料的一组活化片和不带有炭/炭复合材料的另一组活化片同时在铀氢锆脉冲堆的径向实验孔道中进行中子辐照的实验过程。通过比较两组活化片的单核反应率,详细分析了炭/炭复合材料对活化片辐照结果的影响。结果表明,载体采用涂层为Si C的炭/炭复合材料,并且壁厚为几个毫米时,对多种活化片的中子辐照结果影响很小,可以作为高温环境下辐照材料的载体。     

PE/CNT复合材料对空间质子的屏蔽效能仿真分析

随着遥感卫星对观测精度需求的增长,国内外积极探索新型高效质子防护材料。为研究聚乙烯掺杂碳纳米管屏蔽质子效能,本文利用Geant4软件开展质子屏蔽仿真,探究碳纳米管掺杂浓度、管壁直径、排布方式和管壁层数对复合材料质子屏蔽效能的影响规律,并与纯聚乙烯进行对比分析。结果表明,质子屏蔽效能对掺杂浓度、管壁直径和排布方式较敏感,受管壁层数影响相对较小;在高掺杂浓度、大管壁直径和规则排布的情况下,复合材料表现出更优异的质子屏蔽效能;相同质量厚度下,碳纳米管掺杂浓度为10%和20%的复合材料质子屏蔽后的电离剂量分别比纯聚乙烯最大降低了7.40%和12.83%。本文研究结果为辐射防护材料设计提供了数据支撑。     

γ射线辐照对超高分子量聚乙烯/改性纳米伊蒙土复合材料的拉伸性能及热稳定性的影响

采用熔融共混工艺制备超高分子量聚乙烯/改性纳米伊蒙土(Ultra-high molecular weight polyethylene/modified illite-smectite interstratified clay,UHMWPE/M-ISIC)复合材料,将其分别在空气和N_2气氛下γ射线辐照改性。结果表明,UHMWPE/M-ISIC的拉伸强度随M-ISIC添加量增加而先增后减,且在添加量为1%内时达到最大值。空气中辐照后UHMWPE的热稳定性降低明显,而UHMWPE/M-ISIC热稳定性降低不明显,在N_2中辐照后则两者变化都不明显。纯UHMWPE在空气中辐照后其结晶度增大、N_2中辐照后其结晶度减小;UHMWPE/M-ISIC的结晶度在空气和N_2中辐照后都有减小。与纯UHMWPE相比,空气中辐照后UHMWPE/M-ISIC的凝胶含量及抗蠕变能力增加,而N_2气氛下辐照后其凝胶含量以及抗蠕变能力变小。结果表明,在空气辐照后片层结构伊蒙土具有降低氧扩散速率进而减少裂解促进交联,在N_2气氛下则阻碍了分子链的自由活动而阻碍了交联。     

Recent Progresses and Critical Issues of SiCf／SiC Composite Under Irradiation Environments

SiC with fiber-reinforced composites, which are presently considered as the primary structural materials in some fusion reactor conceptual designs, are more attractive and competitive for structural materials in a fusion energy system because of its excellent chemical and mechanical properties such as high fracture toughness, induced-low activation, afterheat under 14MeV neutron irradiation environment at elevated temperature, and good compatibility with coolant and breeder materials. Thus it is important to investigate the research progress of advanced SiC composite, including transmuted helium gas, radiation swelling, radiation effects on mechanical properties, irradiation-enhanced creep, fatigue, physical properties associated with fusion design and their critical issues. This report summarized these results and addressed the major critical issues under irradiation conditions.     

Quantifying helium distribution in dual-ion beam irradiated SiCf/SiC composites by electron energy loss spectroscopy

In this study, we report a method to quantify the helium distribution in the SiC_f/SiC composites, which are used as the first-wall materials of fusion reactor. The helium-bubble formation in Hi-Nicalon Type-S (HNS) was observed in the irradiated SiC_f/SiC composites at a level of 100 dpa and at 800 °C and 1000 °C, respectively. We applied transmission electron microscopy and electron energy loss spectroscopy to investigate the helium-gas-bubbles-formation mechanisms. To simulate the practical first-wall environment of Deuterium–Tritium (D–T) fusion reactor, a dual-ion beam (6 MeV Si³⁺ and 1.13 MeV He⁺) was performed to irradiate the SiC_f/SiC composites. The relationship between the energy shift of He K-edge and the radius of the bubble of the SiC composites was estimated by electron energy loss spectroscopy analysis. The results show that all of the helium atoms irradiated at 1000 °C and formed the bubbles. On the other hand, at 800 °C, only 25.5% of the helium atoms form the helium bubbles. A clear thermal-dependent formation mechanism is found.     

SiC/SiC composite fabricated with carbon nanotube interface layer and a novel precursor LPVCS

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied as promising candidate materials for nuclear applications. Three-dimensional SiC/SiC composite was fabricated via polymer impregnation and pyrolysis (PIP) process using carbon nanotubes (CNTs) as the interface layer and LPVCS as the polymer precursor. The microstructural evolution of the fiber/matrix interface was studied. The porosity, mechanical properties, thermal and electrical conductivities of the SiC/SiC composite were investigated. The results indicated that the high densification efficiency of the liquid precursor LPVCS resulted in a low porosity of the SiC/SiC composite. The SiC/SiC composite exhibited non-brittle fracture behavior, however, bending strength and fracture toughness of the composite were relatively low because of the absence of CNTs as the interface layer. The thermal and electrical conductivities of the SiC/SiC composite were low enough to meet the requirements desired for flow channel insert (FCI) applications.     

Mechanical properties of unidirectional and crossply SiCf/SiC composites using SiC fibers with carbon interphase formed by electrophoretic deposition process

Unidirectional (UD) and crossply (CP) SiC_f/SiC composites with different fiber volume fraction were fabricated based on EPD and sheet stacking process, and their mechanical properties were evaluated at room temperature. The UD-SiC_f/SiC composites showed a pseudo-ductile fracture behavior in bending test. Bending strength and fracture energy of the UD-SiC_f/SiC composites with high V_f (66%) was higher than those of the UD-SiC_f/SiC composites with low V_f (47%). Although the CP-SiC_f/SiC composites also fractured in a non-brittle manner, their bending strength and fracture energy were much lower than the UD-SiC_f/SiC composites because the SiC fibers aligned in 90° direction did not work for toughening and strengthening the SiC_f/SiC composites. In the UD-SiC_f/SiC composites, fiber pullout was clearly observed, and the number of fiber pullout in the UD-SiC_f/SiC composites with high V_f was large rather than the UD-SiC_f/SiC composites with low V_f. On the other hand, fiber pullout did not appear in the CP-SiC_f/SiC composites with low V_f whereas large number of fiber pullout was observed in the CP-SiC_f/SiC composites with high V_f. This can be explained by the thickness of the SiC matrix-layers between SiC fiber-layers.     

Effect of the number of graded layers on the microstructure and properties of SiC/C functionally graded materials

SiC/C bulk functionally graded materials (FGMs) with different numbers of graded layers (N) for fusion technology were designed and fabricated successfully by a power stacking method and hot-pressing process under the pressure of 30 MPa at 2000 °C. Results showed that the number of graded layers (N) had marked effect on the microstructure and properties of the as-received SiC/C FGMs. SEM examinations indicated that interfaces between the adjacent layers faded out gradually and became more linearly continuous gradient with increasing number of graded layers, which led to marked improvement in the bend strength and thermal shock resistance of the samples. Water quenching tests with a temperature difference of 500 °C showed that SiC/C FGMs with N > 8 had the best thermal shock resistance for the materials studies, and no cracks occurred after 90 quench cycles.     

Measurement of tritium production rate distribution in natural LiAlO2/HDPE assembly irradiated by D-T neutrons

A neutronics experiment was performed to measure the tritium production rate (TPR) profile in the breeder assembly with LiAlO₂ as breeder and high density polyethylene (HDPE) as neutron reflector. The breeder assembly was irradiated with 14 MeV neutrons from DT neutron generator at IPR Neutronics Laboratory. The objective of the experiment was to validate the tritium production prediction capability of the Monte-Carlo code MCNP and FENDL 2.1 data library. The tritium production rate profile in the breeding assembly was measured by irradiating Li₂CO₃ pellets kept at various locations and then tritium counting liquid scintillation technique. Experiment was analyzed with 3D Monte-Carlo code MCNP with FENDL 2.1 cross-section data library. The calculation results were found to agree with the measured tritium production rates except one point near to the source. This experiment is a starting experiment in the series of benchmark experiments for the Indian Demo breeding blanket.     

Dynamic energy spectrum and energy deposition in solid target by intense pulsed ion beams

A method for analyzing the dynamic energy spectrum of intense pulsed ion beam (IPIB) was proposed.Its influence on beam energy deposition in metal target was studied with IPIB produced by two types of magnetically insulated diodes (MID).The emission of IPIB was described with space charge limitation model,and the dynamic energy spectrum was further analyzed with time-of-flight method.IPIBs generated by pulsed accelerators of BIPPAB-450 (active MID) and TEMP-4M (passive MID) were studied.The dynamic energy spectrum was used to deduce the power density distribution of IPIB in the target with Monte Carlo simulation and infrared imaging diagnostics.The effect on the distribution and evolution of thermal field induced by the characteristics of IPIB dynamic energy spectrum was discussed.