Droplet Free Metal Ion Sources for PVD Coating production
EPSRC funded GR/R32420 (2001-2003)
To meet continuous demands for improved performance of the state of art hard coatings for tribological applications it is necessary to incorporate novel plasma assisted deposition technology into the present coating equipment providing better control over the energy of film forming species.
The work proposed to build on experience of Sheffield Hallam University in coating and surface engineering, and collaboration with Linköping University, Sweden, which has contributed in the past to the development of High Power Impulse Magnetron sputtering. Ionised magnetron sputtering and high power pulsed magnetron sources provide a high degree of ionization of metal vapour comparable with steered cathodic arc which is currently used for applications where substantial ionisation of metal flux is desirable.
Magnetron sputtering sources generate no droplets unlike arc evaporation, which is crucial for reducing the number of growth defects. This will be used to improve several critical technological steps in wear and corrosion resistant coating production: (a) (Tool coating applications) droplet free metal ion etching during surface pretreatment will lead to high quality coating/substrate interface with reduced film roughness (b) the production of fully dense layers from ionized film forming species interrupting the columnar growth for improved corrosion resistance.
As both modified magnetron plasma sources require only a minimal modification to existing coating equipment, the process and its benefits will be available at a relatively low investment to a wide range of companies (incl. SME's) in the coating and finishing industries.
The outcomes of this research project were: fundamental plasma studies of the HIPIMS discharge - first in-depth characterisation proving the presence of metal ions and doubly charged metal species; temporal evolution of the metal and gas ions in HIPIMS plasma showing gas rarefaction effect and self-sputtering regime; first characterisation of HIPIMS in Ar-N2 atmosphere; development of HIPIMS technology for pre-treatment of substrates prior to coating deposition for the enhancement of adhesion; deposition of first nitride films (CrN) showing high microstructural density and resistance to corrosion and wear; development and plasma analysis of radio frequency coil in industrial size batch coater.