Effect of the Degree of High Power Impulse Magnetron Sputtering (HIPIMS) Utilisation on the Corrosion Properties of TiN Films

Abstract

TiN coatings were deposited by conventional dc unbalanced magnetron (UBM) sputtering, combined High Power Impulse Magnetron Sputtering (HIPIMS)/UBM and pure HIPIMS sources in an industrial size 4 cathode magnetron sputtering machine with a bias of -50V during deposition. Four source combinations were used namely 4UBM (pure UBM), 1HIPIMS+3UBM, 2HIPIMS+2UBM and 2 HIPIMS (pure HIPIMS) for the deposition. Optical emission spectroscopy (OES) measurements revealed that the degree of Ti ion flux increased with increasing number of HIPIMS sources involved in the process. The microstructural characterisation was done by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The potenitiodynamic polarization measurements showed that the pure HIPIMS and 2HIPIMS+2UBM exhibited better corrosion resistance compared to 1HIPIMS+3UBM and pure UBM coatings. The positive shift of Ecorr value from -391 mV for pure UBM coating to +305 mV for 2HIPIMS+2UBM coating was observed. The SEM investigations of corroded samples revealed that the pure UBM coating exhibited more number of corrosion pits which is a clear sign of aggressive corrosion than the other three coatings. Raman analysis showed that pure UBM and 1HIPIMS+3UBM coating corroded more and allowed the electrolyte to react with the substrate as oxides due to substrate contribution can be seen on the surface. Moreover 2HIPIMS+2UBM and pure HIPIMS coating surfaces were free from these oxides due to highly dense microstructure. The cross section TEM analysis exhibited the void free high density coating with weak column boundaries deposited by pure HIPIMS sources.