Microstructural evolution and mechanical properties of the joint of TiAl alloys and C/SiC composites vacuum brazed with Ag-Gu filler metal

摘要

Microstructural evolution and shear strength of vacuum brazed TiAl alloys to C/SiC composites using Ag-Cu filler metal were investigated. The dissolution of active elements Ti and Al from TiAl substrate has a strong influence on the microstructure and shear strength of the joint. Ag is the less active element of the filler and Cu has strong tendency to the formation of AlCu_2Ti phase with the dissolved Ti and Al. Ag-Cu eutectic is gradually taken place by AlCu_2Ti blocks and Ag-based solid solution with the increase of brazing temperature or time. The TiC reaction layer including a small amount of Ti_5Si_3 phase is formed adjacent to C/SiC composites when active element Ti diffused into C/SiC composite and chemical reaction occurred in the composite interface. The shear strength of the joint depends heavily on the thickness of the TiC reaction layer. The maximum shear strength achieved 85 MPa for the joint vacuum brazed at 900 °C for 10 min. Cracks primarily propagate along Ag-rich phase and TiC layer. The TiC layer with the thickness of 4-5 nm is formed at the boundary of SiC matrix.