Corrosion Behavior of Ti-Cr-N Coatings on Tool Steel Substrates Prepared Using DC Magnetron Sputtering at Low Growth Temperatures

In this research, Ti-Cr-N coatings on tool steel were prepared using DC magnetron sputtering at 25 degrees C (RT), 130 degrees C and 190 degrees C. Coating corrosion behavior was observed in a 3.5% NaCl solution at 25 degrees C using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS). EIS circuit models for corrosion kinetics were proposed and the surface area and porosity of the coatings were recorded. Corrosion resistance was found to be higher for the coatings grown at 190 degrees C. This could be attributed to high density as well as low porosity. The EIS circuit model suggests the penetration of corrosive electrolytes into pores reaching the steel substrate for the coatings grown at RT. Finite length diffusion inside pores was also observed. The slow infiltration of corrosive electrolytes into the steel substrate could be seen in coatings grown at 130 degrees C with diffusion inside the pore similar to that in the coatings grown at RT. However, the EIS circuit model did not exhibit a finite length diffusion of the coatings grown at 190 degrees C. Owing to high coating density and smaller pore size, corrosive electrolytes could hardly penetrate through and reach the steel substrate.