Influence of joining time and temperature on the flexural strength of joined boron carbide ceramics

The influence of the joining time and temperature on the flexural strength of B4C ceramics joined using an Al sheet was investigated. The B4C ceramics were joined over a temperature range 600–1400°C for 2–72 h in vacuum (10−2–10−4 Pa) and in an Ar atmosphere. A joining interlayer with a dense structure was found in the B4C joint formed at 1000°C after 2 h in vacuum, and mainly Al was present in this joining interlayer. On the other hand, some voids existed in the joining interlayer in the B4C joint formed after 72 h. In addition, Al was not present in this interlayer owing to its reaction with B4C as well as the evaporation of Al. Four-point bending tests of the B4C joints formed at 1000°C in vacuum for periods ranging from 2 to 72 h were performed at room temperature. The average four-point bending strengths of the B4C joints formed after 2 h at 700–1100°C were close to that of the B4C base material, and the B4C ceramics were considered to have successfully bonded. However, the joint strength decreased with an increase in the joining time, and the B4C ceramics did not bond at temperatures over 1200°C in vacuum. On the other hand, the B4C ceramics did bond at 1200–1400°C in Ar.