Design of Novel Buffer Layers for Excellent Performance UHTCs; Investigation of Diffusion Mechanisms

新型缓冲层设计，实现卓越性能的 UHTC；

• 批准号: 323778385
• 负责人: Professor Dr. Hans-Joachim Kleebe
• 金额: --
• 依托单位: Institut für Angewandte Geowissenschaften (IAG)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/323778385?language=en
• 关键词: Design; Novel; Buffer; Layers; Excellent

ZrB2 is an ultra-high temperature ceramic (UHTC) possessing a melting point exceeding 3000°C and interesting engineering and physical properties. As such, ZrB2 ceramics are considered potential candidates for space and hypersonic components. The main drawbacks that restrict the employment of ZrB2 ceramics for a wider spectrum of applications are mainly related to its low damage tolerance, poor oxidation resistance and relatively high density. However, the introduction of discontinuous SiC fibers can both increase the toughness of ZrB2 above 6 MPa·m½ and parallel a notably decrease in density. Moreover, the addition of secondary phases such as MoSi2 can further improve the high-temperature strength and, most importantly, the oxidation performance of the boride matrix. The ultimate scope of the project is to obtain a functionally graded (FG) composite made up of a ZrB2-MoSi2 outer scale to provide oxidation and ablation resistance and a progressively SiC fiber-enriched body from top to bottom to guarantee a higher failure tolerance and a lower density of the entire structure. The major obstacle to overcome is the detrimental chemical reaction between Mo-compounds and SiC fibers occurring during sintering, which leads to the microstructural degradation of the fibers and, hence, to the loss of their toughening function.To reach the above mentioned aim, the focus of the project is on the development of a novel ZrB2-based buffer scale able to prevent chemical reactions between SiC fibers and Mo-compounds and on the study of interdiffusion processes across the interface, both during sintering and upon oxidation. It is envisioned to utilize mixtures of ZrB2 and Si3N4, SiCN and HfSiN for the diffusion barrier. The understanding of the chemical reactions across the various layers will be fundamental for the design of a novel UHTC for applications under extreme environments.The work plan foresees the development of various baseline ceramic joints with different composition of the buffer layer and a thorough microstructural characterization of the as-sintered and oxidized specimens by transmission electron microscopy. These analyses, coupled to thermodynamic predictions, will be essential in revealing local diffusion processes and will lead to the definition of an optimized buffer layer composition for the design of a functional UHTC. Thermo-mechanical characterization and arc-jet tests of the optimized composite will be carried out to assess the performance of the novel material.

ZrB2是一种超高温陶瓷（UHTC），熔点超过3000°C，具有有趣的工程和物理性能。因此，ZrB2陶瓷被认为是空间和高超音速部件的潜在候选者。限制ZrB2陶瓷广泛应用的主要缺点主要是其低损伤容限，较差的抗氧化性和相对较高的密度。然而，引入不连续的SiC纤维可以使ZrB2的韧性提高到6 MPa·m½以上，同时密度也显著降低。此外，添加二次相如MoSi2可以进一步提高高温强度，最重要的是，提高硼化物基体的氧化性能。该项目的最终目标是获得一种功能梯度（FG）复合材料，该复合材料由ZrB2-MoSi2外壳组成，以提供抗氧化和抗烧蚀能力，并从上到下逐渐富集SiC纤维，以保证整个结构具有更高的容错能力和更低的密度。需要克服的主要障碍是烧结过程中mo化合物和SiC纤维之间发生的有害化学反应，这会导致纤维的微观结构降解，从而失去其增韧功能。为了达到上述目标，该项目的重点是开发一种新型的基于zrb2的缓冲垢，能够防止SiC纤维和mo化合物之间的化学反应，并研究烧结和氧化过程中界面上的相互扩散过程。设想利用ZrB2和Si3N4、SiCN和HfSiN的混合物作为扩散屏障。了解不同层之间的化学反应将是设计一种适用于极端环境的新型UHTC的基础。该工作计划预测了具有不同缓冲层组成的各种基线陶瓷接头的开发，并通过透射电子显微镜对烧结和氧化样品进行全面的显微组织表征。这些分析与热力学预测相结合，对于揭示局部扩散过程至关重要，并将为设计功能性UHTC提供优化缓冲层组成的定义。将对优化后的复合材料进行热力学表征和电弧喷射试验，以评估新材料的性能。