Microstructure and mechanical properties of physical vapor deposited Cu/W nanoscale multilayers: Influence of layer thickness and temperature

Based on our previous knowledge on Cu/Nb nanoscale metallic multilayers (NMMs), Cu/W NMMs show a good potential for applications as heat skins in plasma experiments and armors, and it could be expected that the substitution of Nb by W would increase the strength, particularly at high temperatures. To check this hypothesis, Cu/W NMMs with individual layer thicknesses ranging between 5 and 30 nm were deposited by physical vapor deposition, and their mechanical properties were measured by nanoindentation. The results showed that, contrary to Cu/Nb NMMs, the hardness was independent of the layer thickness and decreased rapidly with temperature, especially above 200 °C. This behavior was attributed to the growth morphology of the W layers as well as the jagged Cu/W interface, both a consequence of the low W adatom mobility during deposition. Therefore, future efforts on the development of Cu/W multilayers should concentrate on optimization of the W deposition parameters via substrate heating and/or ion assisted deposition to increase the W adatom mobility during deposition.