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

Abstract

Abstract:The SiC/SiC joints were vacuum brazed at 700 ℃, 740 ℃, 780 ℃ and 800 ℃ 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/Ti 5 Si 3 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.

Mechanical behavior of SiC joints brazed using an active Ag‐Cu‐In‐Ti braze at elevated temperatures

“…For SiC/SiC joints brazed with Ag‐Cu‐Ti (Cusil ABA), the reaction layer is typically reported to comprise of a TiC layer adherent to the SiC (having a film like morphology) and a Ti 5 Si 3 adherent to the TiC layer (having a scale like morphology) . Similarly for Incusil ABA brazed SiC/SiC joints, a layered structure of the reaction layer was observed by Liu et al, with the addition that a layer mainly rich in In, Si, and Ag (and minor additions of Ti, C and Cu) was found in‐between the SiC interface and the TiC layer. Liu et al proposed that during brazing the TiC‐layer cracks or delaminates allowing liquid braze material to flow into the formed gap and consequently leading to the formation of this additional In‐containing layer (adjacent to SiC).…”

“…The joining was conducted under vacuum (≤10 −4 mbar). A final brazing temperature of 740°C and a holding time of 10 minutes (Figure D) were chosen as Liu et al reported this is where a maximum of bending strength of SiC/SiC joints as a function of brazing temperature may occur.…”

“…The most commonly used tests to characterize the mechanical performance of the joints are bending and shear tests. A maximal room temperature (RT) four‐point bending strength of SiC/SiC joints brazed with Cusil ABA (900°C/10 min) of 342±69 MPa or ~234 MPa for joints brazed with Incusil ABA has been reported in the literature. However, the brazing filler composition, the brazing parameters, the brazing layer thickness, the joint microstructure especially the interfacial reaction products and residual stresses in the interfacial zone can all strongly affect the measured joint strength .…”

“…The mechanical behavior of brazed SiC joints at elevated temperature is not well characterized, the data available in the literature have been summarized in Table . To our knowledge, only Liu reported the bending test values of SiC joints brazed with Cusil ABA and Cusil ABA/SiC particles tested up to 600°C. A significant decrease (by 54%) of the flexural strength of SiC/Cusil ABA/SiC joints down to around 155 MPa was already observed at a temperature of 300°C.…”

“…Hereby, brazing has been industrially proven as a reliable and practical joining process for the manufacture of complex ceramic components. 3 Commercially available Ag-based active brazing fillers such as Cusil ABA (Ag-35.3Cu-1.75Ti, in wt.%), [4][5][6] Ticusil (Ag-26.7Cu-4.5Ti, in wt.%), 6 Incusil ABA (Ag-32.25Cu-12.5In-1.25Ti, in wt.%) 7 as well as laboratory-made Ag-Cu filler [8][9][10][11][12][13][14][15][16] have been used for brazing SiC ceramics due to their good wettability characteristics. [17][18][19][20][21] The most commonly used tests to characterize the mechanical performance of the joints are bending and shear tests.…”