A study of defects in sputtered TiN coatings by electrochemical polarization

Abstract

Reactively rf‐sputtered TiN coatings were studied by taking electrochemical polarization measurements in an aerated 0.01N HCl aqueous solution. The substrate materials were Fe‐based alloy INCOLOY 800 and Ni‐based ODS alloy MA 6000. The effects of sputtering process parameters, such as deposition time, power, nitrogen partial pressure, bias voltage, and substrate temperature were studied. The electrochemical polarization of the thin coatings was compared with the polarization of the uncoated substrates. The observed polarization behavior of TiN coatings was correlated to structural details studied by scanning electron microscopy. The results of these tests are presented and discussed. TiN coatings produced by optimized parameters proved to be completely dense. The changes in process parameters gave clear indication in electrochemical polarization behavior. Some structural defects, such as nodules, were clearly indicated in the electrochemical measurement. The polarization measurements offer a sensitive method for discovering the existence of open porosity and other open structural defects, which are difficult to localize using other methods, and for determining the microstructural quality of the sputtered TiN coatings.