超高温陶瓷纤维增强超高温陶瓷基复合材料的界面相的理论预测与实验验证

Ultrahigh-temperature ceramics (UHTCs) are regarded as the materials of choice for nose tips and sharp leading edges of hypersonic vehicles, and hot structure components of scramjet engines. However, the intrinsic brittleness, poor thermal shock resistance, and difficulty in machining into complex shapes have hampered the applications of the current ZrB2-and HfB2-based UHTCs in hypersonic vehicles. To circumvent these obstacles, emerging ultrahigh-temperature ceramic fiber reinforced ultrahigh-temperature ceramic matrix (UHTCf/UHTC) composites must be implemented. The advantages of future UHTCf/UHTC composites include low density, high thermal conductivity, good thermal shock resistance, superior fracture toughness and defect tolerance. In designing and manufacturing future UHTCf/UHTC composites, fiber-matrix interphase plays a determining role to ensure load transfer, fiber pull-out and toughening. High melting point, low shear deformation resistance and high volume expansion upon oxidation are the basic requirements for interphase materials of future ultrahigh-temperature ceramic fiber reinforced ultrahigh-temperature ceramic matrix (UHTCf/UHTC) composites. Unfortunately, the interphase materials for future UHTCf/UHTC composites are not available yet. In this project, a combination method of first-principles calculations and experimental verifications will be used search for novel interphase materials for future ultrahigh-temperature ceramic fiber reinforced ultrahigh-temperature ceramic matrix (UHTCf/UHTC) composites. To meet the requirements of interphase materials for future UHTCf/UHTC composites, high melting points transition metal borides and carbides are selected as candidate materials. Through calculating the second order elastic constants and predicting the elastic properties of polycrystalline materials, low shear deformation resistance, high expansion upon oxidation and the mechanical and thermal properties that are comparable to those of UHTC fibers and UHTC matrix will be chosen. Then, some candidate materials are prepared and tested to prove the suitability of them as interphase materials for future UHTCf/UHTC composites.

由于受到超高温陶瓷的脆性、抗氧化性和抗热冲击性能较差的限制，发展超高温陶瓷纤维增强超高温陶瓷基(UHTCf/UHTC)复合材料是超高温陶瓷发展的必然趋势。未来UHTCf/UHTC复合材料将具有低密度、高热导率、良好的抗热冲击性和抗损伤性等优异的综合性能。其中界面相对UHTCf/UHTC复合材料的性能起关键作用。对界面相的要求包括高熔点、低剪切模量及高温氧化时产生高体积膨胀。然而，目前对UHTCf/UHTC复合材料界面相的研究尚未开展。本项目拟采用第一原理理论预测和实验验证相结合的方法设计新型UHTCf/UHTC复合材料的界面相。为了使界面相满足未来UHTCf/UHTC复合材料的要求，将以高熔点的过渡金属硼化物和碳化物为对象，通过单晶二阶弹性常数和多晶弹性性能的预测选择具有剪切模量低、高温氧化体积膨胀大及与超高温陶瓷纤维和基体匹配的化合物，并通过材料合成和性能测试验证作为其界面相的适合性。

针对高超声速飞行器的发展对未来新型超高温陶瓷纤维增强超高温陶瓷基复合材料(UHTCf/UHTC)的需求，采用第一原理计算和实验验证相结合的方法开展UHTCf/UHTC 复合材料界面相的设计研究。重点选择高熔点和氧化后产生高体积膨胀的后过渡金属硼化物和碳化物为研究对象，通过对单晶二阶弹性常数的计算和多晶体模量B、剪切模量G 和弹性模量 E的计算，预测具有剪切模量低、剪切与体模量比值 (G/B) 低、高温氧化时体积膨胀率较大、并与超高温陶瓷纤维和基体匹配的化合物作为UHTCf/UHTC 复合材料界面相的候选材料，然后通过材料合成、力学和热学性能测试，验证所选择的材料作为 UHTCf/UHTC复合材料界面相的可能性。已经预测出了NiB、YB2C2、Y2B3C2、MB6 (M=过渡金属或稀土金属原子)、Cr2AlB2、 Cr3AlB4、 Cr4AlB6、MoAlB、WAlB、Y5Si2B8、Cr5Si3B、 Hf5Si3B、M2YSi (M=Rh, Ir)、YAlB4、Y5Si3C 和 Y3Si2C2新型界面相材料。系统研究了它们的电子结构、晶体结构与力学和热学性能的关系及高温氧化行为，为未来新型超高温陶瓷纤维增强超高温陶瓷基复合材料(UHTCf/UHTC)的设计和制备提供了界面材料的选择余地。项目完成过程中在J. Mater. Sci. Tech., Acta Mater., J. Europ. Ceram. Soc., J. Am. Ceram. Soc.等国内外学术期刊发表论文46篇,发表的论文被SCI引用273频次。