SiC/Ti基复合材料C/Mo双涂层界面改性机理研究

The surface of SiC fiber used as reinforcement of Ti-matrix composites usually has C coating currently, which is used to protect the fiber and slow down the thermal residual stresses. However, C coating is feasible to react with the matrix to form a brittle reaction layer, which leads to great thermal residual stresses around the interface as well as the reaction layer is feasible to crack initially during the loading process, and C coating can be comsumed quickly. Mo has excellent interfacial stability, and it can make its surronding Ti alloy β stabilized to have beter toughness.Therefore, Mo coating will be introduced as interfacial modification layer on the basis of SiC fiber (W core, with a diameter about 100 μm) having C coating in this projiect, which is used to improve the fiber/matrix interfacial compatibility and the mechanical properties of SiC/Ti composites. The formation rule and mechanism of the interfacial zone in the SiC/Ti composites with C/Mo duplex coating after fabrication and thermal exposure in vacuum will be studied systematically, and the effct of interfacial microstructure evolution on the interfacial mechanical behavior (such as interfacial bonding strength, interfacial debonding failure mode and the distributions of thermal residual stresses in the interfacial zone) will be analyzed. Furthermore, the effect of interfacial reaction diffusion on tensile strength of the composites and on the crack propagation behavior will be studied, and the microscopic nature will be revealled from the areas of fiber, matrix and interface. This work will lay a theoretical foundation for the interfacial optimal design of SiC/Ti composites and for longer service life at high temperature.

目前用于增强Ti基复合材料的SiC纤维表面通常带有C涂层，用以保护纤维和缓解界面附近较大的热残余应力。但C涂层易于与基体反应形成脆性反应层，导致界面附近产生较大的热残余应力和反应层在承载过程中易于首先开裂，而且C涂层会不断地被消耗。Mo的界面稳定性优良，而且Mo能使其附近的Ti合金被β化而韧塑性增加。因此，本项目提出在SiC 纤维有C涂层的基础上，再次引入Mo涂层作为界面改性涂层，以进一步改善纤维/基体界面相容性和提高 SiC/Ti 基复合材料力学性能。将系统研究制备态和不同真空热暴露处理后界面微区的组织结构形成规律和机理，分析界面微区组织结构演变对界面力学行为的影响机制；掌握界面反应和元素扩散对复合材料抗拉强度、裂纹扩展行为的影响规律，并从纤维、基体和界面等角度揭示其微观本质，为 SiC/Ti基复合材料界面优化设计、延长其高温使用寿命奠定理论基础。

本项目针对SiC/Ti基复合材料在高温制备和高温服役条件下存在较强的界面反应，使复合材料力学性能降低的背景条件下，提出了在传统SiC纤维有C涂层的基础上，引入一定厚度的Mo金属涂层进行界面改性，即C/Mo双涂层体系界面改性。系统研究了C/Mo双涂层对SiC/Ti6Al4V复合材料界面微观组织结构和力学性能的影响规律和机理。研究结果表明，制备态SiC/C/Mo/Ti6Al4V复合材料的界面相序列为SiC|C|Mo|TiC|Moresidual + β-Ti|αprimary + β-Ti|Ti6Al4V，Ti和C原子沿着Mo涂层的柱状晶晶界向Mo涂层中相对扩散，在Mo涂层中间位置生产了厚度约为300nm的TiC薄层，Mo元素部分地扩散到基体中，使得界面附近基体被β化；C/Mo双涂层在700℃以下真空热暴露时较为稳定，界面相结构无明显变化，750℃下合适的热暴露处理使复合材料的抗疲劳性能达到最佳，但800℃以上热暴露时C/Mo涂层的消耗速率较快，且Mo涂层比C涂层的消耗速率更快，使靠近界面的基体中有TiC和Ti-Al-C化合物生成，从而降低了复合材料的力学性能。此外，本项目还探索研究了C/Mo双涂层对SiC/TiAl基复合材料界面反应的影响规律，发现Mo涂层具有优良的界面热稳定性，且C/Mo双涂层比C单涂层具有更好的界面反应阻碍效果。本项目的研究成果对于高性能SiC/Ti基复合材料的研制具有重要的参考价值。