A comparative study of the corrosion performance of TiN, Ti(B,N) and (Ti,Al)N coatings produced by physical vapour deposition methods

Thin film coatings produced by physical vapour deposition methods often exhibit porosity. Local defects can cause local and rapid corrosion of the base material. The porosity is difficult to estimate and electrochemical methods are most suitable for evaluating the corrosion resistance of the coated material. This paper compares the corrosion resistance of TiN, Ti(B,N), (Ti,Al)N- and TiB2-coated ASP 23 high speed steel. For the materials studied here the corrosion performance of TiB2-coated samples was poor. Ti(B,N) coatings obtained by two different methods were quite similar even though the calculated porosity of the coating produced by magnetron sputtering was lower than that of coatings produced by the electron beam technique. These coatings had similar or slightly better corrosion resistance than (Ti,Al)N coatings with a high aluminium-to-titanium ratio. (Ti,Al)N coatings with a low aluminium-to-titanium ratio were better than coatings with a high aluminium-to-titanium ratio. TiN coatings were better than other types excluding (Ti,Al)N + AlN layer coatings, which performed best. (Ti,Al)N + AlN coatings have an insulating layer on top of the coating, which increases the polarization resistance and decreases the corrosion current density.