Crack propagation behavior of a tungsten copper duplex structure subjected to thermal loading

Thermal fatigue tests were performed on tungsten-copper brazed specimens within the designed temperature range of design temperature of the Fusion Experimental Reactor (FER) divertor collector plates. Two types of brazing fill metals (nickel-based and titanium content silver-based metals) were selected for bonding the tungsten and oxygen-free high-conductivity (OFHC) copper specimens. After the 3000-thermal cycle test, different propagation behavior was observed between two types of specimens. Cracks were initiated in the tungsten near the bonded interface when the nickel-based brazing metal was employed as a brazing filler metal. On the other hand, cracks were initiated in the interface between tungsten and copper and propagated along the interface in the case of silver-based filler metal. These experimental results are discussed using thermal stress and the apparent K-value analyses