Salt spray corrosion and electrochemical corrosion characteristics of CAIP and LTPN fabricated AlCrN/NL composite coating

Abstract

An AlCrN/nitrided layer (NL) composite coating was fabricated on H13 hot work mould steel using a cathodic arc ion plating (CAIP) and low temperature plasma nitriding (LTPN). The surface and cross–section morphologies, chemical composition and phases of obtained coating were characterized using a scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and x-ray diffractometer (XRD), respectively. The salt spray corrosion (SSC) and electrochemical corrosion properties of AlCrN/NL coating in 3.5 wt% NaCl solution were analyzed using a salt spray corrosion chamber and electrochemical workstation. The results show that the AlCrN/NL composite coating consists of AlN, Cr1.75V0.25N2, AlCrFe2 and SiC phases, the formation of ceramic phases increases its corrosion resistance. The aggressive Cl– is adhered on the corrosion products after the SSC test, the corrosive micro–cells and pitting corrosion are formed due to the differences of structure and relative potentials. The corrosion current densities of AlCrN/NL coating, NL and substrate are 3.255 × 10–6, 9.848 × 10–6, and 1.522 × 10−5 A · cm–2, respectively, indicating that the corrosion resistance of AlCrN/NL coating is higher than that of NL and substrate. The polarization resistance of 11 798 Ω · cm2 on the AlCrN/NL coating is 1.68 and 3.67 times higher than that of NL and substrate, respectively, which shows that the AlCrN/NL coating increases the corrosion resistance of substrate.