Investigation of the Process Oriented Microstructure Formation of Gas Flow Sputtered Titanium Coatings

Abstract

Gas Flow Sputtering (GFS) belongs to the group of the Physical Vapour Deposition techniques (PVD) like Electron Beam Vapour Deposition and Magnetron Sputtering. The special characteristic of GFS is the additional gas inlet and gas flow respectively, which transports the sputtered material from the source to the substrate. Argon is used as working gas. In comparison to the other PVD-techniques GFS operates in a high pressure range from 0.3 to 0.7 mbar. Furthermore, the gas flow allows coating areas which are not in line-of-sight without an additional substrate movement. The work performed by GFS aims at the goal to coat simple planar geometries as well as complex parts and shapes with different materials, e.g. a turbine blade or the inside of a tube. The influence of different process parameters on the microstructure formation of sputtered Titanium-coatings is investigated, e.g. pressure, bias voltage and distance. Substrate geometry and position in the gas flow were varied as well. The analysis of the microstructure was executed by Scanning Electron Microscopy. The crystal structure of the coatings was examined by X-Ray Diffraction (XRD). The results show that only a bias voltage during coating process causes a striking change in microstructure. Their flake looking surface and their fine columnar structure have changed into a dense structure. XRD measurements confirmed this visual change. At all tests the hexagonal phase of pure titanium has occurred, but by the use of a bias voltage the strong texture of the phase has disappeared. The contrary effect could be demonstrated for the parameter substrate temperature. Pre-heating the substrate to a temperature at 0.3 T/Tm has amplified the texture. In contrast the parameters distance and pressure had no significant influence on the microstructure.