采用Ti3Si(Al)C2对SiC/SiC复合材料改性的新方法及其抗氧化机理

On one hand, it is a difficult problem to fabricate dense SiC matrix composites reinforced with Hi-Nicalon SiC fiber (Hi-Nicalon SiC/SiC) at temperatures lower than 1200 C. On the other hand, the low fracture toughness of matrix restricts the properties of dense SiC/SiC composites. The above problems limit its widely applications. Focusing on the urgent needs of high thrust-weight ratio jet engine on dense SiC/SiC composites, the present proposal will develop a low-melting-point melt infiltration method (MI). By low-melting-point MI process, Ti3Si(Al)C2 as a ceramic with high fracture toughness will be in-situ formed in SiC/SiC composites, which will be prepared by chemical vapor infiltration (CVI), so that residual silicon will be avoided in the MI SiC/SiC compoistes to increase the toughness of matrix. The research contents include: the microstructure design and near-net fabrication mechanisms of Ti3Si(Al)C2 modified SiC/SiC composites; the influence of Ti3Si(Al)C2 on the mechanical properties and oxidation resistence of SiC/SiC composites; the oxidation-resisting mechanisms of Ti3Si(Al)C2 modified SiC/SiC composites. We propose to fabricate a novel Ti3Si(Al)C2 modified SiC/SiC composite by low-melting-point MI process at temperatures lower than 1200 C, which may not only avoid the microstructure evolution of Hi-Nicalon SiC fiber during MI, but also optimize the phase composition and microstructure of MI SiC/SiC. The proposed research will be beneficial to improve both material and process of SiC/SiC composites, and enrich the oxidation-resisting theory of SiC/SiC compoistes. The results will promote the applications of Hi-Nicalon MI SiC/SiC composites in jet engines.

Hi-Nicalon SiC纤维增韧SiC基复合材料（SiC/SiC）在1200℃以下难致密且基体韧性低，这是制约其应用的瓶颈。针对航空发动机对致密SiC/SiC的迫切需求，本项目拟发展低熔点熔体渗透（MI）法，在SiC/SiC内原位生成高韧性Ti3Si(Al)C2，以取代低韧性的残余硅。研究改性SiC/SiC的微结构设计/制备机理、Ti3Si(Al)C2对SiC/SiC力学性能和抗氧化性能的影响规律、改性SiC/SiC的抗氧化机理。基于低熔点MI法探索制备新型Ti3Si(Al)C2改性SiC/SiC，不但可避免Hi-Nicalon SiC纤维在复合材料致密化过程中的微结构演变，而且可优化SiC/SiC的基体相成分和微结构。本项目将完善SiC/SiC复合材料的材料体系及工艺体系，丰富SiC/SiC复合材料的抗氧化理论，为Hi-Nicalon SiC/SiC在航空发动机上的应用奠定基础。

SiC纤维增韧SiC基复合材料在较低温度下难致密且基体韧性低，制约了其广泛应用。针对航空发动机对致密SiC/SiC的迫切需求，本项目采用浆料浸渗结合Al-Si合金渗透的方法在1300C实现了Ti3Si(Al)C2改性SiC/SiC复合材料的制备，相比于传统液硅渗透工艺其致密化温度降低了300C。基于此工艺相继开展了Ti3Si(Al)C2生成机理、复相陶瓷力学性能、复合材料力学性能和抗氧化性能的研究。Al-Si合金渗透过程中，Al能够有效降低TiC的晶界能，从而实现较低温度下Ti3Si(Al)C2的制备；基于Al-Si合金较低的熔点，能够在1300C时实现SiC/SiC复合材料的低温快速致密化，并在基体内部原位自生Ti3Si(Al)C2；大量“可塑性”基体弥散分布于复合材料纤维束内部，给材料带来新的断裂机制，从而使得SiC/SiC-Ti3Si(Al)C2表现出良好的强韧性；通过对于材料在不同温度下抗氧化性能的研究，揭示了Ti3Si(Al)C2的引入对于材料抗氧化性能的影响机制。本项目的研究成果拓展了Ti3Si(Al)C2的制备途径及用途，通过基体塑性变形丰富了陶瓷基复合材料内部的增韧机制，为陶瓷基复合材料的强韧化提供了新的思路。SiC/SiC-Ti3Si(Al)C2的抗弯强度和韧性分别为485MPa和24MPa•m1/2，相比于传统SiC/SiC其制备周期缩短了1/3。本项目成功实现了致密SiC/SiC复合材料的低温致密化，为致密SiC/SiC在航空发动机中的应用奠定基础。