Ir coating prepared on Nb substrate by double glow plasma

Compact and adhesion Ir coating was obtained on the surface of the Nb substrate by double glow plasma method which had a deposition chamber and two cathodes. Argon gas was used as the working gas. The bias voltage of Ir target and Nb substrate were −950 V and −300 V, respectively. The chamber pressure was 35 Pa. Microstructure and morphology of the Ir coating was examined by the X-ray diffraction and scanning electron microscopy, respectively. The Ir coating had a poly-crystalline structure with preferential growth orientation of (2 2 0) crystal plane. The deposition velocity was ∼5.7 μm/h. The good adhesion resulted from the buffer layer between the Nb substrate and the Ir coating. The Nb concentration distributed gradiently along the depth of the buffer layer. Because the target and the substrate were the cathode electrodes, the Nb and Ir were continuously deposited and sputtered out on the Nb substrate surface. For the higher bias voltage of the target, sputtered Nb atoms were suppressed by intense Ir atoms and formed a mixed boundary layer on the Nb substrate surface. With the Ir and Nb deposition, the Nb element in the as-deposited film gradually decreased and led the Nb atoms content decrease in the boundary layer.