Investigation on Different TiCn Duplex Treatments Applied to Cold Work Tool Steel for Surface Properties Improvement

In this work, different plasma nitriding and coating thickness combinations were tested to improve surface proprieties of a cold work tool steel. A DIN X100CrMoV8-1-1 cold work tool steel was plasma nitrided, using a 5 vol-%. N2 + 95 vol-% H2 gas mixture, for 2.5- and 5.0-h nitriding times. Then, the non-nitrided and nitrided substrates were coated with titanium carbonitride (TiCN)-graded thin films produced by cathodic arc plasma-assisted physical vapor deposition. Different deposition parameters were used to produce coatings with thicknesses of 1.0 and 2.0 µ m. The samples were characterized regarding the microstructure, surface hardness, coating adhesion, and friction coefficient, which were measured by ball-on-disc tests. In the plasma nitriding process, it was possible to generate a diffusion layer, without the formation of a compound layer, with depths of 58 µ m and 68 µ m for 2.5 and 5.0 h, respectively. Both plasma nitriding treatments avoided delamination of the TiCN coating when deposited on the cold work tool steel. The TiCN coatings significantly decreased the friction coefficient, regardless of substrate condition. The lowest friction values were found for the thinner coating. The deeper diffusion zone led to higher hardness value, and highest scratch crack propagation resistance of the coatings, meaning superior coating adhesion. The best surface properties were found when combining the deeper plasma nitriding diffusion layer with the thinner PVD coating.