Fig nbsp xA Specific heat capacities of W Cu
Some basic characteristics of the coatings including oxygen content, porosity, density and microhardness are displayed in Table 2. The oxygen contents of the APS-85W/15Cu and APS-75W/25Cu coatings measured by nitrogen/oxygen analyzer were about 1.31 wt.% and 1.43 wt.%, respectively, while those ICG-001 of the VPS-85W/15Cu and VPS-75W/25Cu coatings were only 0.65 wt.% and 0.76 wt.%, respectively. The lower oxygen contents of VPS-W/Cu coatings compared with those of APS-W/Cu coating are owing to the intrinsic feature of VPS technology. However, there is some air still left in the chamber due to the vacuum level, which result in oxygen impurity. Porosity determined by the Archimedes' method in the APS-W75/Cu25 coating is 11.5%, while it is only 6.0% in the VPS-W75/Cu25 coating. The density of VPS-W/Cu coating is significantly higher than that of APS-W/Cu coating with the similar Cu content. With the increase of Cu content the hardness value decreases, but higher hardness values are obtained for the VPS-W/Cu coatings as compared with the APS-W/Cu coatings, which can be explained by their lower porosities and less oxidation .