Improved hardness and corrosion resistance of iron by Ti/TiN multilayer coating and plasma nitriding duplex treatment

A duplex treatment of plasma nitriding followed by deposition of a Ti/TiN multilayer coating was performed on commercial pure iron. Plasma nitriding was carried out using high frequency low bias voltage plasma immersion ion implantation (HLPIII), and the Ti/TiN multilayer films were deposited using unbalanced magnetron sputtering on the nitrided iron surface. The plasma nitriding layer was 4 μm thick, consisting of mainly ε-Fe3N and γ-Fe4N. The microhardness of the iron with Ti/TiN multilayer coating + plasma nitriding duplex treatment was over 18 GPa, somewhat harder than that of iron with a Ti/TiN multilayer film but without plasma nitriding, and almost 5 times that of the (only) nitrided iron. The film-cohesion for Ti/TiN multilayer film on the nitrided substrate was much better than that on the substrate without nitriding treatment. Comparing with the Ti/TiN film on bare iron, the samples with Ti/TiN multilayer coating + plasma nitriding duplex treatment have better corrosion resistance.