CORROSION OF TIN, (TIAL)N AND CRN HARD COATINGS PRODUCED BY MAGNETRONSPUTTERING

Metallic components like moulds, dies and machinery can be subjected t o intensive degradation during plastic transformation processes, namel y when working with fibre filler materials and plastics which release F, S or Cl during transformation. The degradation is attributed to the combined erosive and abrasive wear by the filler material and corrosi ve attack of agents. This degradation reduces the lifetime of the comp onents considerably and has a direct impact on process productivity an d surface finish of the final products. Nitride-based hard coatings li ke TiN, (TiAl)N, BN, etc. have proved their capability to increase too l lifetime when exposed to abrasive and corrosive environments found i n plastic transformation processes (halogenated polymers, acrylics, po lyesters, fibre reinforced plastics, etc.). Within the frame of this w ork we produced TiN, (TiAl)N, CrN hard coatings, with and without a me tallic interlayer, by de and rf reactive magnetron sputtering, with a thickness of about 2 mu m. The aqueous corrosion behaviour of the coat ings was studied in saline and acidic environments by potentiodynamic and open circuit potential (OCP) measurements. The oxidation resistanc e during annealing in air was also studied. In saline (NaCl 9%) and ac id (HCl 3.4%) environments we found that a metallic interlayer of Ti o r Cr in the case of TiN-(TiAl)N-coated samples and CrN-coated samples, respectively, generally improve the corrosion resistance. Best result s for all tested nitride coated samples were obtained for the Ti0.27Al 0.73N coating. The OCP vs. Saturated Calomel Electrode (SCE) (60 min) measurements indicated that most samples were nobler than the un-coate d substrate. The mentioned potentials depend on the deposition conditi ons and the film microstructure. Most of the coatings lose some of the ir protective capabilities after an high temperature annealing. In con trast to the Ti-based hard coatings, the corrosion resistance of CrN i s improved by a 800 degrees C annealing treatment in air. (C) 1998 Els evier Science S.A.