Influences of Al, Cu, and Au joining materials on the flexural strength and microstructure of joined boron carbide ceramics

Abstract

Joining technology is a promising method for producing large–sized or complex boron carbide (B4C) ceramics. As joining materials significantly affect the mechanical properties of B4C joints, the influences of Al, Cu, and Au joining materials on the microstructure and properties of B4C ceramics joined in a temperature range of 700–1600 °C for 2 h in vacuum (10−2–10−4 Pa) were investigated. The four-point bending strength of a B4C joint formed using Al metal was close to that of the B4C base material. However, the strength of a Cu-containing B4C joint was lower than that of the B4C joint formed using Al, and the B4C joint fabricated using Au metal exhibited the lowest strength among the samples investigated. A joining interlayer with a dense structure was formed in the Al-containing B4C joint at 1000 °C after 2 h in vacuum, which mainly included Al metal and small amounts of compounds produced during the reaction of B4C with Al. Meanwhile, voids were present in the joining interlayer of the Cu-containing B4C joint formed at 1500 °C after 2 h in vacuum, which was exclusively composed of Cu species. The microstructure of the Au-containing B4C joint was similar to that of the B4C joint formed using Cu metal. After the alkali corrosion testing of the manufactured B4C joints, the four-point bending strength of the Al-containing B4C joint decreased from 254 to 82 MPa. For comparison, the strength of the Cu-containing B4C joint was reduced from 211 to 178 MPa, whereas the strength of the Au-containing B4C joint did not change. Therefore, Cu and Au were the most effective B4C bonding materials for alkaline corrosive environments.