Hybrid TiN-CCPN coating of AISI-201 stainless steel by physical vapor deposition combined with cathodic cage plasma nitriding for improved tribological properties

Abstract

The poor mechanical properties of AISI 201 stainless steel under harsh environment limit its uses in modern building structures, automobiles and aerospace industry. Various technologies, such as physical vapor deposition (PVD) and cathodic cage plasma nitriding (CCPN) at different temperatures, are being used to reduce wear and tear of metals but the optimal method with acceptable results is still under development. In this paper, a novel duplex surface coating method, coupled with DC pulsed CCPN, was used to develop anti-wear and anti-corrosive TiN-coating over AISI 201 stainless steel. The CCPN, TiN coatings over AISI 201 stainless steel were performed in alternative manner and characterized for surface hardness, surface morphology, wear rate, chemical composition and erosion rate. XRD analysis revealed the formation of iron nitride and titanium nitride planes in the coated samples when compared with base materials. The TiN coated coupons exhibited reasonably good tensile strength, which increased manifold on CCPN treatment. The CCPN treated TiN coated coupons showed very low wear rate, wear volume and erosion rate among all the tested samples. Scanning probe microscopy was used to study the erosion rate and topology of the base and coating coupons under different water jet velocities. The erosion rate of base coupon at a jet velocity of 5 m/s was measured about 1.27 mm/year, which fell to 0.25 mm/year after duplex coating. The results show that duplex coatings, when applied in the proper order, can improve mechanical qualities by reducing wear rate, erosion rate, and wear volume.