Corrosion resistance of TiN/TiAlN-coated ADI by cathodic arc deposition

Abstract

Because of its low cost, high tensile strength, fatigue resistance, and wear resistance, austempered ductile iron (ADI) has been utilized in a wide variety of mechanical applications. However, in opposition to the versatility of the above-mentioned mechanical properties, the shortcomings of ADI are its surface hardness (Hv: 396) and corrosion resistance. And, because its relatively low austempering temperature falls in the range of Ms–450 °C (Ms: the martensite start temperature), ADI cannot be case hardened using traditional high temperature heat treatment. This study explored the effects of TiN and TiAlN coatings on ADI, with respect to surface hardness and corrosion resistance. The process employed for coating TiN/TiAlN onto ADI involved variable target current low temperature cathodic arc deposition (CAD). The coating characteristics and corrosion resistance of TiN/TiAlN-coated ADI were analyzed for further understanding of the feasibility of the low temperature CAD coating process. The analysis showed that TiN and TiAlN films could successfully be coated onto ADI through CAD technology without altering the unique microstructure of ADI. Utilizing a variety of target currents in the coating process yielded an acceptable level of adhesion while raising the surface hardness of ADI by a factor of 2–4 (Hv: 396 versus 1356–1910). It was observed that as target current increased, the surface roughness of the specimens also increased. TiN/TiAlN-coated ADI specimens exhibited higher corrosion resistance than uncoated ones when both were immersed in separate solutions of both 3.5 wt% NaCl and 10 vol.% HCl. Conclusively, the application of TiN and TiAlN films to ADI through the coating process of low temperature CAD is a viable surface modification for ADI applications that require increased surface hardness and corrosion resistance.