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

碳化硅因其优异的耐热性和耐腐蚀性而被期望作为恶劣环境下的燃气轮机和核聚变反应堆的结构材料，但在实际应用中，有必要提高一些与晶粒相关的机械性能。因此，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-碳化硅晶界微观结构可以通过选择掺杂元素(Mg、Al、P)和改进烧结工艺(热压、研究发现，Si 和掺杂剂之间的离子半径失配越大，晶粒生长就越促进。此外，放电等离子体烧结产生的频率较高。 (2)晶界微观结构对机械性能的影响：断裂强度和显微硬度随着晶粒尺寸的减小而增加，以“Hall-Petch关系”的方式观察到晶粒尺寸敏感性的关系。取决于晶界特征分布，随着特殊晶界频率的增加，断裂强度和显微硬度增加。(3)掺杂剂和晶界微观结构对高温氧化和氧化的影响。氧化引起的脆化：无论掺杂元素如何，都观察到被动氧化，特别是，掺镁 SiC 中的氧化显着增强，并且质量增益比未掺杂 SiC 大约高一个数量级，特别是在 Mg- 中。掺杂SiC，即使发生被动氧化，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）来改善强度下降。 (4)掺杂元素和环境对摩擦磨损性能的影响：发现SiC在无润滑条件下的摩擦磨损性能取决于掺杂元素和相对湿度(RH)，在较低湿度(30%RH)下。），掺杂元素（Mg、Al、P）的影响更为明显，在未掺杂条件下，摩擦系数约为 0.8，而在较高湿度下，掺杂元素（Mg、Al、P）的摩擦系数降至 0.4。 (60%RH)，摩擦系数约为0.25，且与掺杂元素无关。