CORROSION RESISTANCE OF PLASMA-ASSISTED CHEMICAL-VAPOR-DEPOSITION (PACVD) TIN-COATED STEEL IN A RANGE OF AGGRESSIVE ENVIRONMENTS

The protective effects of plasma-assisted chemical vapour deposition ( PACVD) TiN layers deposited at 570-720 degrees C on the corrosion, act ive dissolution and passivation of high speed steel in H2SO4, H3PO4 an d NaOH solutions have been estimated. The effect of the deposition tem perature was found to manifest itself through the quality of the TiN l ayer and interphase formed at the various temperatures studied. The ef fect of the TiN porosity varies in the different solutions and depends on the electrochemical behaviour of the substrate in those solutions. In the active (H2SO4) or passive (NaOH) state of the substrate the ef fect of the layer porosity is less pronounced than in the case of a so lution causing the active as well as the passive state of the substrat e (H3PO4). The effect of the TiN layer porosity can be overshadowed by the effect of the interphase quality. TiN produces different effects on the corrosion, anodic dissolution and passivation of coated steel s ince it has different effects on the individual cathodic and anodic pr ocesses.