A study of microstructures and corrosion behavior of HVOF/PVD duplex coating against 10 vol% HCl solution

Abstract

Injection mold for ABS+PVC mixture confront severe HCl severe corrosion, resulting in its short service lifetime. To overcome this problem, a duplex coating, consisting of an inner thick anti-corrosion NiCr-30Cr3C2(containing 30 wt% Cr3C2) interlayer and an outermost nano-composite TiSiN coating, was designed and provided by combination of High Velocity Oxygen Fuel (HVOF) and physical vapor deposition (PVD). The results show that the NiCr-30Cr3C2interlayer is composed of γ-NiCr and Cr3C2phases, with high-density defects (Pores, Cracks and Un/semi-melted zones), whereas the TiSiN coating consists of fcc nanocrystallines embedded amorphous Si3N4 matrix, also containing high-density micro-particles. The corrosion experiments against 10 vol% HCl solution at 65 °Cshow that the HVOF-PVD duplex coating displays a much superior corrosion resistance compared to single HVOF layer or PVD coating. Poor corrosion resistance of NiCr-30Cr3C2 layer is mainly due to the strong destruction of chlorine ions on the passivation films and its high-density defects which are prone to the infiltration of electrolyte, whereas poor anti-corrosion of TiSiN coating is attributed to the TiSiN-coating delamination caused by coupling effects of particle-induced pitting corrosion, interfacial corrosion and cracking. While the superior corrosion resistance of HVOF/PVD duplex coating is associated with the chemical inertness of TiSiN coating and the existence of the anti-corrosionNiCr-30Cr3C2interlayer which effectively inhibits interfacial corrosion and the generation of cracks. This indicates that the HVOF/PVD duplex coating may be as a good candidate for injection molds under HCl environments.