Abstract
In order to achieve a high-quality joint between SiO2f/SiO2 and metals, it is necessary to address the poor wettability of SiO2f/SiO2 and the high residual stress in SiO2f/SiO2-Nb joint. Here, we simultaneously realize good wettability and low residual stress in SiO2f/SiO2-Nb joint by combined method of HF etching treatment and Finite Element Analysis (FEA). After etching treatment, the wettability of E-SiO2f/SiO2 was improved, and the residual stress in the joint was decreased. In order to better control the quality of joints, efforts were made to understand the relationship between surface structure of E-SiO2f/SiO2 and residual stress in joint using FEA. Based on the direction of FEA results, a relationship between residual stress, surface structure and joint property in the brazed joints were investigated by experiments. As well the FEA and the brazing test results both realized the high-quality joint of E-SiO2f/SiO2-Nb and the shear strength of the joint reached 61.9 MPa.
Highlights
SiO2f/SiO2, one of the most significant functional and structural quartz fiber reinforced silica ceramic matrix composites, has been attracted great attention in aerospace industry applications, due to its high thermal shock resistance, excellent ablation resistance as well as low thermal conductivity[1,2,3,4,5,6]
The structure introduced the residual stress among the braided quartz fibers, which complicated the distribution of the residual stress in the joint
The interface analysis was first performed on the brazing joints before and after etching treatment, evidencing the establishment and the application of model for Finite Element Analysis (FEA)
Summary
Microstructure of the joint brazed with and without etching treatment. The interface analysis was first performed on the brazing joints before and after etching treatment, evidencing the establishment and the application of model for FEA. The shear strength of the joints decreased with the etching depth increasing over 100 μm, because of the residual stress in the joints was increasing by the τxy of the “3D-pinning structure”, according to the FEA results (see Fig. 12). The results show clearly that the etching treatment plays a key role in two major aspects on active brazing SiO2f/SiO2 and Nb. On the one hand, it can effectively improve the wettability of SiO2f/SiO2, which is a precondition of successfully brazing SiO2f/ SiO2 and Nb. On the other hand, it can induce the brazing alloy infiltrating into E-SiO2f/SiO2, which increases the bonded area, reduces the residual stress and enhances the mechanical properties. As well the FEA and the brazing test results both reveal that the properties of 100 μm@SiO2f/SiO2-Nb joint is the best among the obtained brazed joints with different surface structures
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