Surface wetting and interfacial behaviour in arc brazing of titanium alloy

The spreading behaviour of Cu, CuSi, CuMnNi, and TiCuNi filler metals with Ti6Al4V titanium alloy base metal has been studied under gas tungsten arc welding heating. Test results showed that the wet angle of CuMnNi filler metal was the smallest (150) and that of Cu was the largest (30degrees). With spreading, the liquid filler metal solidified and crystallised simultaneously, and formed a spherical crown brazing seam. The wettability and spreadability of the liquid filler metal were related to oxide scale actions with arc heating. These actions included the 'cleaning action of the cathode' and lashing activation action of electrifying ions and electrons. Furthermore, the very high temperature of the activation spot zone partly melted the base metal surface and near surface metal, and a thin liquid film was accordingly formed that created a strong heating activation. It was also discovered that there was a column solid-liquid incongruent compound eta(MeTi2) at the interface of filler metal and base metal (Me + Cu, Cu + Ni, Cu + Mn). This compound grew to form an interface with the centre of the brazing seam and was embedded in it. The particular crystallising and growing mode in the arc heating helped grow the column solid-liquid incongruent compound eta(MeTi2). (C) 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining.