Relationship between Grain Boundary Microstructure, Chemistry and Mechanical Properties in Silicon Carbides

碳化硅晶界微观结构、化学和机械性能之间的关系

基本信息

批准号：
12450277
负责人：
TSUREKAWA Sadahiro
金额：
$ 8.06万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

Silicon carbide has been expected as a structural material for gas turbine and nuclear fusion reactor in severe environments for example because it possesses excellent heat-resistance and corrosion-resistance. However, for practical applications, it is necessary to improve some mechanical properties related to grain boundary such as intergranular fracture, high-temperature oxidation-induce embrittlement and wear resistance. The objective of this project therefore was to obtain the knowledge concerning grain boundary microstructure and chemistry for achieving enhanced mechanical properties. The chief results obtained are summarized as follows.(1) Effects of materials processing and dopant on grain boundary microstructure: Grain boundary microstructure in β-silicon carbides could be controlled by selecting doping element (Mg, Al, P) and modifying sintering processing (hot-pressing, spark plasma sintering). It was found that the larger ionic radius mismatch between Si and dopant, the more … More grain growth was enhanced. Moreover, the spark plasma sintering yielded a high frequency of low energy special boundaries.(2) Effect of Grain Boundary Microstructure on Mechanical Properties: Fracture strength and microhardness increased with decreasing grain size with the manner of "Hall-Petch relation". Of particular importance was the observation that the grain size sensitivity in the relation depended on the grain boundary character distribution. Fracture strength and microhardness increased with increasing the frequency of special boundaries.(3) Effects of Dopant and Grain Boundary Microstructure on High-Temperature Oxidation and Oxidation-Induced embrittlement: Passive oxidation was observed irrespective of doping elements. In particular, oxidation in Mg-doped SiC was remarkably enhanced and the mass gain was approximately one order higher than undoped SiC. A remarkable strength degradation was observed, particularly in Mg-doped SiC even though passive oxidation took place. We have found that the strength degradation can be improved by decreasing the frequency of general boundaries (increasing the frequency of special boundaries) and grain size.(4) Effects of Doping Element and Environment on Friction and Wear Properties: It was found that the friction and wear properties of SiC in unlubricated condition depended on doping elements and relative humidity (RH). At lower humidity (30%RH), the effect of doping elements (Mg, Al, P) was more pronounced. In undoped condition, the friction coefficient was approximately 0.8. The friction coefficient reduced to 0.4 with Mg-doping. At higher humidity (60%RH), the friction coefficient was 〜0.25 and was independent of doping elements. Less

例如，在严重环境中，碳化硅被预期是燃气轮机和核融合反应堆的结构材料，因为它具有出色的耐热和耐腐蚀性。但是，对于实际应用，有必要改善与晶界相关的某些机械性能，例如晶间断裂，高温氧化引起的靠着和耐磨性。该项目的目的是获得有关晶界微观结构和化学的知识，以实现增强的机械性能。（1）材料加工和掺杂剂对晶界微观结构的影响：β-硅碳纤维中的晶界微观结构可以通过选择掺杂元件（MG，AL，P）来控制晶粒边界微观结构并修改烧结加工（热压力，火花等离子体的血浆杀伤）。发现SI和掺杂剂之间的离子半径不匹配较大，谷物的生长越多。此外，火花等离子体烧结产生了低能特殊边界的高频。（2）晶界微观结构对机械性能的影响：断裂强度和微硬度随着晶粒尺寸的减小而随着“霍尔 - - - - - 奇异关系”的方式而增加。特别重要的是，观察到关系中的晶粒尺寸灵敏度取决于晶界特征分布。断裂强度和微硬度随着特殊边界的频率的增加而增加。（3）掺杂剂和晶界微观结构对高温氧化和氧化诱导的覆盖的影响：观察到被动氧化，无论掺杂元素如何。特别是，掺杂mg的SIC中的氧化显着增强，质量增益大约比未掺杂的SIC高一个阶。观察到了显着的强度定义，尤其是在掺杂MG的SIC中，即使发生了被动氧化。我们发现，可以通过降低一般边界的频率（增加特殊边界的频率）和晶粒尺寸来提高强度定义。（4）掺杂元件和环境对摩擦和磨损特性的影响：发现非润滑条件下SIC的摩擦和磨损性能取决于掺杂元素和相对湿度（RH）。在较低的湿度（30％RH）下，掺杂元件（Mg，Al，p）的影响更为明显。在不稳定的条件下，摩擦系数约为0.8。摩擦系数随着mg掺杂而降低到0.4。在较高的湿度（60％RH）下，摩擦系数约为0.25，与掺杂元件无关。较少的