Hybrid-Sulfnitriding of Ion-Nitriding and Sputtering

SCM 435 was plasma-sulfnitrided at 823K for 3.6-18ks in a 30% N2-70% H2 mixing gas atmosphere at 665Pa by hybrid-treating ion-nitriding and sputtering of MoS2. MoS2 was positioned 20mm above the specimen and applied discharge voltages of 300-600V. Sulfnitriding layers formed on the specimen's surface were evaluated by EPMA, X-ray diffraction, microscopic observations and microhardness changes. A 4-μm nitride (γ'-Fe4N) layer and a 400-μm nitrogen diffusion layer formed on specimens ion-nitrided without applying an electric potential. A 12-μm compound layer of sulfide (FeS) and nitride (ε-Fe2-3N and γ'-Fe4N) formed beneath the sulfide, and a 400-μm nitrogen diffusion layer formed on the surface of specimens plasma-sulfnitrided by applying an electric potential of 500V. The compound layer formed in plasma-sulfnitriding was thicker than in ion-nitriding. The compound layer thickness and surface hardness depend on specimen temperature, treatment time and the electric potential applied to MoS2. Mo and S were included in plasma-sulfnitrided compound layers. Surface hardness after plasma-sulfnitriding is higher than after conventional sulfnitriding. This may be due to Mo sputtered from the MoS2 target.