Damage development of sintered SiC ceramics with the depth variation in Ar ion-irradiation at 600 ℃

Irradiation damage of the materials depends on the irradiation dose and the intrinsic property of the material. In this paper, the high purity hot pressing sintered SiC ceramics with very few second phase and excellent crystallinity were prepared as the target materials, and the high irradiation dose up to 0.95 and 3.16?dpa respectively were chosen. The as-sintered SiC ceramics were irradiated with a 160?keV Ar ion beam at 600?°C. X-ray photoelectron spectroscopy, Raman spectrum, transmission electron microscopy and nanoindentation tests were utilized to analyze the microstructure variations on the surface of irradiated SiC, and it was found that the irradiated crystals kept crystallinity, although amorphization of SiC was generated with 10–25?nm depth, following with a mixture of point defect clusters and extended defects. Furthermore, it is also evident that there is a balance between irradiated-induced damages buildup and dynamic annealing of defects in high temperature.     

Laser irradiation of α-SiC ceramics

The process of laser irradiation of a surface of SiC ceramics in air was investigated. As a result of SiC oxidation and evolution of CO₂, porous SiO₂ forms on the target surface. During deposition of ablation products on the substrate, a loose SiO₂ film forms.     

Wetting behavior of AgCu–Ti filler metal on SiC ceramics surface pre-treated by ion bombardment

For the first time, the wetting behavior of SiC ceramics modified by ion bombardment was studied and the interfacial microstructure was characterized. An amorphous layer was formed on the SiC surface, which has significant influence on the wetting behavior and the interfacial microstructure of SiC/AgCu–Ti wetting system. The interfacial reactions were accelerated when filler melted on the bombarded SiC surface, and the spreading on the bombarded SiC ceramics was controlled by interfacial reactions firstly and then by diffusion. The spreading rates, k_r, were denoted as k_r,i = 42.28exp (-456.2/RT) for bombarded SiC, and k_r,0 = 28.62exp (-329.9/RT) for the original one. Ion bombardment improved the bonding quality of ceramics/droplet interface effectively, a mixed reaction layer containing TiC and Ti₅Si₃ was formed and no reactant stratification was occurred at the interface of SiC/droplet.     

基于核应用下碳化硅陶瓷及其复合材料的连接研究进展

SiC陶瓷及其复合材料凭借其自身固有的核辐射下的稳定性而有望成为新一代核裂变以及未来核聚变反应堆中重要的结构材料.能否满足核应用环境下各种苛刻条件而实现完美连接是其能够得到最终应用的关键.本文综述了目前国际上基于核应用上SiC陶瓷及其复合材料的几种连接工艺的发展情况.     

Effects of helium irradiation on fine grained β-SiC synthesized by spark plasma sintering

Silicon carbide has a high resistance to irradiation making it a material of choice for use in the nuclear reactors. In this work, we focus on experiments involving implantation of 30 keV ³He ions at room temperature (RT) in sintered β-SiC. Helium is produced in large quantities in fission and fusion reactors, and its accumulation in materials can lead to the formation of bubbles. The irradiation induces structural modifications within the material that can be coupled with changes in composition, especially at high fluence. Three ion fluencies are used here: 5 × 10¹⁵, 1 × 10¹⁷and 1 × 10¹⁸at. cm⁻². Structural damages are studied by electron microscopy and helium profiles are measured by nuclear reaction analysis (NRA). At 1 × 10¹⁸ at. cm⁻², helium bubbles are formed in the implanted zone, which also undergoes strong oxidation. Surface blisters are also observed and helium concentration threshold for bubble formation is estimated to about 4 at. % by correlating the MET observations with the results obtained by ion beam analysis. For the highest fluence, a residual concentration of 3.6 × 10¹⁷ at. cm⁻² was measured just after implantation (instead of 1 × 10¹⁸ at. cm⁻²), which indicates a significant release of helium by the material during the process. The link between the microstructural evolution of the material, its progressive oxidation under beam and the release of helium is discussed. The very likely role played by the porosity on the oxidation of the material under irradiation at RT is underlined. Finally, the results obtained here on silicon carbide are compared with those obtained on another ceramic (TiC) which does not amorphize in similar conditions.     

Mechanical behaviour of reaction processed SiC ceramics from artificial precursor from plant

Mechanical behaviour of SiC ceramics synthesized from two artificial precursors from plants – coir fibreboard and bamboo pulp fibreboard – was studied and the mechanical properties – flexural strength, Young's modulus, fracture toughness and hardness – of the ceramics synthesized from the two kinds of artificial precursors were compared. The effect of processing of the artificial precursors, as reflected in the microstructure of the ceramics synthesized from them, was taken into consideration in the analysis of the mechanical property data; these data could also be possible to be explained by the empirical models of fracture mechanics. The results of the study established the possibility of application of the investigated SiC materials as structural ceramics.     

碳化硅陶瓷材料成型工艺的研究进展

介绍了SiC陶瓷材料的成型工艺,综述了这些工艺的优缺点,并重点介绍了挤出成型工艺。     

流延成型法制备SiC多孔陶瓷工艺的研究

本实验通过采用流延成型工艺制备碳化硅多孔陶瓷过滤材料 ,经过比较分析总结出pH值对泥浆性能的影响 ,当浆料的pH值为 7-9时出现大量絮状物 ,导致流动性和悬浮性能都很差 ,当浆料的pH值小于 7时 ,浆料的流动性急剧下降 ,导致无法流延。合适的浆料pH值范围为 >11。流延成型后的试样经过干燥脱模后在 95 0～ 12 5 0℃温度下烧结 ,制得气孔率随着烧成温度的不同而变化的样品 ,其中在 10 5 0℃ ,样品最高气孔率为 5 2 %,通过SEM观察 ,10 5 0℃的制品的孔径平均在 6.5 μm左右 ,气孔分布均匀 ,气孔通道类型微直通道 ,而且成网状结构分布     

先驱体聚碳硅烷的合成研究进展

介绍了近年来先驱体聚碳硅烷(PCS)的制备、性能和应用的研究现状和进展。着重介绍了合成先驱体PCS的主要方法：常压循环热裂解法、高压法、常压催化法和常压高温裂解法。比较了这几种合成方法的优缺点：从用PCS制备陶瓷纤维的用途来说，高压法是一种较成熟的方法，所制备的陶瓷SiC纤维的性能也较好，但装置复杂、成本较高、安全性较差；常压高温裂解法合成装置简单、成本较小、安全性也好，但使用该法制得的陶瓷SiC纤维的性能较差。     

碳化硅陶瓷材料的制备工艺和应用研究进展

碳化硅陶瓷材料由于具有轻质高强、导热性能好、膨胀系数低、硬度高、抗氧化等优异的性能,被广泛用作高温结构部件。本文围绕碳化硅材料在光学反射镜材料的应用,对碳化硅材料的制备工艺和应用方面的进展作简要综述。     

反射镜材料的选择及SiC反射镜的应用

本文从反射镜材料选择的基本要求出发,以材料的热物理性能、力学性能、光学可加工性、化学稳定性和安全性为依据,认为SiC材料是今后反射镜材料的首选,另外还介绍了SiC反射镜的应用领域以及提出了未来SiC材料用作反射镜时的一些建议.     

碳化硅晶须对氧化锆陶瓷材料结构的影响

本文研究了不同晶须含量对可相变增韧的ZrO_2(2mol%Y_2O_3)陶瓷及完全稳定的ZrO_2(6mol%Y_2O_3)陶瓷结构的影响。结果表明:晶须的加入使ZrO_2材料的晶料明显细化,但对该类热压复合材料的致密度影响不大;纯ZrO_2(6mol％Y_2O_3)为单一的C相结构,加入晶须后有少量的t相出现;纯ZrO_2(2mol%Y_2O_3)热压材料由t m两相组成,晶须的加入降低了基体中m相的相对含量,但对断裂过程中t→m相交量影响不大。     

SiC多孔陶瓷预成形坯的制备

本文采用真空烧结方法制备SiC多孔陶瓷预成形坯,研究了不同助烧结剂Al2O3-Y2O3、Si、Co和高岭土以及造孔剂羧甲基纤维素(CMC)含量对SiC多孔陶瓷预成形坯气孔率和形貌的影响。结果表明,多元助烧剂Al2O3-Y2O3有利于降低烧结温度和形成液相烧结,并有利于提高SiC多孔陶瓷的孔结构稳定性;羧甲基纤维素含量对烧结预成形坯气孔率和体积密度的影响较大,随着造孔剂CMC含量的增加,SiC多孔陶瓷的气孔率也相应地增加,其体积密度相应减少。     

Fabrication of wood-like porous silicon carbide ceramics without templates

The porous silicon carbide ceramics with wood-like structure have been fabricated via high temperature recrystallization process by mimicking the formation mechanism of the cellular structure of woods. Silicon carbide decomposes to produce the gas mixture of Si, Si₂C and SiC₂ at high temperature, and silicon gas plays a role of a transport medium for carbon and silicon carbide. The directional flow of gas mixture in the porous green body induces the surface ablation, rearrangement and recrystallization of silicon carbide grains, which leads to the formation of the aligned columnar fibrous silicon carbide crystals and tubular pores in the axial direction. The orientation degree of silicon carbide crystals and pores in the axial direction strongly depends on the temperature and furnace pressure such as it increases with increasing temperature while it decreases with increasing furnace pressure.     

Fabrication of porous silicon carbide ceramics with high porosity and high strength

Unique porous SiC ceramics with a honeycomb structure were fabricated by a sintering-decarburization process. In this new process, first a SiC ceramic bonded carbon (SiC/CBC) is sintered in vacuum by spark plasma sintering, and then carbon particles in SiC/CBC are volatized by heating in air at 1000 °C without shrinkage. The honeycomb structure has at least two different sizes of pores; ∼20 μm in size resulting from carbon removal; and smaller open pores of 2.1 μm remaining in the sintered SiC shell. The total porosity is around 70% and the bulk density is 0.93 mg/m³. The bending and compressive strengths are 26 MPa, and 105 MPa, respectively.