A study of the wetting, microstructure and bond strength in brazing SiC by Cu-X(X=Ti,V,Nb,Cr) alloys

Abstract

In the active brazing of SiC by copper-based alloys, the effects of various active elements such as titanium, vanadium, niobium and chromium on the wetting, microstructure and bond strength are investigated. In wetting, Cu-Cr alloys have the lowest wetting angles on SiC of 10 degrees-20 degrees depending on the chromium content. SiC is decomposed on contact with alloy melts during brazing. Carbon and silicon released from this decomposition of SiC react with active elements to produce their carbides and silicides at the interface. The reacted layers have different microstructures depending on the brazing alloys, but Cu-Ti and Cu-Cr alloys show similar microstructure, as do Cu-V and Cu-Nb alloys. In the four-point bend tests, the brazed joints of Cu-5 at % Ti, Cu-5 at % V and Cu-5 at % Nb alloys have similar bend strengths of 86.9, 80.3 and 92.4 MPa, respectively. The brazed joints of Cu-2 at % Nb alloys show a high bend strength of 154 MPa, although the wetting angle is a little higher, at about 60 degrees. Niobium is found as a new active element of copper-based alloys to braze SiC. Cu-Nb alloys are promising for substitution for Cu-Ti alloys.