Development of W/Cu-functionally graded materials

Plasma facing components (PFCs) consist of a plasma facing and a heat sink material. These have to fulfil different functions that require different material properties, for example the coefficient of thermal expansion (CTE) of tungsten and copper. Joining of these materials (e.g. by brazing or HIPing) results in the formation of thermal-induced stresses at the interface. Functionally graded materials (FGMs), used as an interlayer, reduce these thermally induced stresses. Two different methods, laser sintering and plasma spraying, have been investigated as a means to produce W/Cu FGMs to be used in PFCs of next step confinement experiments. In addition to mixtures of tungsten and copper powders, 40 wt.% Cu-coated W powder was used to produce W/Cu composites with a content of either 25 or 60 vol.% Cu. The composite microstructure has been analyzed according to Cu content, particle distribution and layer structure. The difference in the behavior of powder mixtures and coated powder is outlined. A comparison of plasma sprayed to commercially produced Cu-infiltrated W samples is made and the results of thermomechanical and thermophysical testing are discussed with respect to different microstructures.