Study of corrosion and tribo-corrosion performance of AISI 420 stainless steel nitrided and coated with AlCrN

Abstract

AISI 420 martensitic stainless steel is used in different applications where high mechanical resistance and a good corrosion behaviour are required. In order to improve their surface properties and their wear resistance various treatments can be used [1]. In this work, the corrosion and tribo-corrosion behaviour of AISI 420 steel nitrided and coated with AlCrN was s t udi e d and c ompar e d i t wi t h t he s ame s t ee l o nl y c oa t ed and ni t ri ded. The microstructure was analysed usi ng XRD and SEM, and nanohardness was measured. Scratch and Rockwell C tests were used to evaluate adhesion. Salt spray tests were carried out according to ASTM B117. Cyclic potentiodynamic polarization curves were used to evaluate corrosion behaviour and also EIS was conducted after one hour and after five days of exposure to a NaCl solution. The tribo-corrosion tests were performed in NaCl solution for 7200 s, and the OCP was measured during the test. The coating and the nitrided layer thickness was 3.7 ± 0.2 µm and 12.7 ± 0.5 µm respectively. The AlCrN coating hardness was around 32 GPa, whil e the ni tri ded layer was about 18 GPa. Ni trogen expanded mart ensite and some Fe nitri des were detected i n the ni tri ded layer us ing XRD. The adhesion was better in the nitrided and coated sample (duplex) than in the only coated one. The critical load was 80 N and 60 N for duplex and coated samples respectively in the scratch test. The nitrided and only coated samples showed better behaviour than the duplex one in the electrochemical tests after five days. The same performance was observed in Salt Spray Tests. However, the duplex sampl e showed a nobler OCP and showed the best behaviour in the tribocorrosion tests.