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.

Reaction‐bonded B4C (RBBC) was fabricated through molten Si infiltrating porous B4C preforms. A preform with a 75% relative green density was obtained by mixing two different sized B4C powders. Carbon black added to the preform slightly reduces average pore size, but increases porosity. RBBC ceramics showed a dense and homogeneous microstructure. Vickers hardness was about 15 GPa for RBBC fabricated from a single type of B4C powder and could reach 22–23 GPa for the carbon‐added samples after infiltration. Morphological evolution and the influence of the microstructure on the Vickers hardness were investigated and discussed.

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