Mechanical properties and microstructural stability of CuTa/Cu composite coatings

In this study, the structure and mechanical properties of as-deposited and 823.15 K annealed CuTa coatings were studied with the purpose to evaluate the microstructural and mechanical thermal stability as a function of the Ta content. CuTa coatings with a Ta content from 0 to 100% were prepared by magnetron co-sputtering. Their structure and mechanical properties were characterized by grazing angle X-ray diffraction (XRD), scanning and transmission electron microscopy (TEM), and nanoindentation. The XRD results show that a Ta-rich CuTa glass metal is formed in the coatings with 15–67 at.% Ta along with nanocrystalline Cu and such microstructure was retained after vacuum annealing at 823.15 K. TEM analyses of selected samples showed the formation of crystalline Cu islands in an amorphous CuTa matrix in both as-deposited and annealed coatings. The coatings presented a 3D distribution of Cu nanocrystals within an amorphous CuTa matrix which might reduce the brittleness of the glassy CuTa matrix. A significant increase in hardness values from 0.9 GPa for pure Cu to 11.9 GPa for the sample with 98 at.% Ta is observed. It has been shown that the composite coatings preserved the microstructure and were mechanically stable after vacuum annealing. [Display omitted] •3D distribution of Cu nanocrystals within a Ta-rich CuTa amorphous matrix•Microstructural and mechanical stability after annealing at 823.15 K•Coatings are mainly metallic, with a very thin oxide layer.•Cu nanocrystals were protected against oxidation by the Ta-rich CuTa amorphous layer.