Microstructure of reaction layer and its effect on the joining strength of SiC/SiC joints brazed using Ag-Cu-In-Ti alloy

The SiC/SiC joints were vacuum brazed at 700 degrees C, 740 degrees C, 780 degrees C and 800 degrees C for 10 min respectively, using Ag-Cu-In-Ti active filler alloy. The microstructure and joining strength of the joints were characterized by electron probe X-ray microanalyser (EPMA), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and four-point bending strength test. The interface of the joints was composed of three parts: SiC substrate, reaction layer and filler alloy. A representative microstructure of the reaction layer: In-containing layer/TiC layer/Ti5Si3 layer was found from the TEM image. The forming of the In-containing layer could be attributed to the crack or delamination of SiC/TiC interface. The In-containing layer intensified the coefficient of thermal expansion (CTE) mismatch of SiC and the reaction layer, and affected the joining strength. With the increase of the reaction layer's thickness, the joining strength firstly increased, then declined, and the maximum four-point bending strength reached 234 MPa.