Plasma vapor deposition hard coating on pre-nitrided low alloy steel

Ion-nitrided samples of the hardened and tempered low alloy steel 40Cr was coated by a TiN layer by hot chemical deposition (HCD) ion plating. By this complex treatment combining ion-nitriding with subsequent ion plating, the surface hardened layer was composed of a thin outermost coating layer of TiN with a hardness of approximately 2300 Hv, a thin compound layer of ε+γ′ with a hardness of 800–1000 Hv and a thicker inner diffusion layer of approximately 600–800 Hv. X-Ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM) results showed that a α-Fe layer (black layer) is not observed on the interface between compound layer and TiN layer after duplex treatment. At the interface, Ti reacted with N from the compound layer to form a TiN layer and ε-Fe2–3N transformed into γ′-Fe4N partially.