Phase equilibria effects in enhanced liquid phase sintering of tungsten-copper

A tungsten-copper (W-Cu) bond is a reference design concept for a divertor collector plate in the Fusion Experimental Reactor (FER). In the present study, durability of the W-Cu bond under thermal cycling was experimentally examined. A plasma spraying technique was applied to form a tungsten layer with a thickness of around 2 mm on a copper disk. This technique has advantages in that tungsten can be deposited on curved and complex surfaces of substrates and that the temperature of the substrate can be kept low during the deposition. Two kinds of copper materials, oxygen-free high conductivity copper (Cu/OFHC) and copper alloyed with beryllium (Cu/Be), were used. The tungsten surface of the W-Cu test piece was periodically irradiated with a high temperature argon plasma jet under the thermal stress condition corresponding to that expected at the normal operation of the FER. The thermal properties of the plasma sprayed tungsten were measured before the test, and the microstructure before and after the test was investigated with a scanning electron microscope. The sprayed tungsten layer was found stratified and had porosity of 2–3 % before the test. The W-Cu/OFHC test piece survived for thermal cycle up to 6000, while the W-Cu/Be test piece broke between 4500 and 5000 cycles.