Abstract
A duplex treatment of plasma nitriding (PN), followed by the deposition of a CrN/CrTiAlSiN/WCrTiAlN multilayer coating, was performed on AISI 4140 steel. Untreated, plasma-nitrided, only-coated (just the coating) and duplex-treated (PN + coating) AISI 4140 steel were microstructurally and mechanically characterized. The nitrided compound layer, consisting of mainly ε-Fe2-3N and γ′-Fe4N phases, was approximately 8.0 μm thick. The total thickness of the multilayer coating, which consisted of a top W-Cr-Ti-Al-N multilayer, a periodic Cr-Ti-Al-Si-N interlayer, and a CrN bottom layer, was 2.3 μm. The CrN/CrTiAlSiN/WCrTiAlN multilayered coatings possessed a super-hardness of 47.9 GPa and the highest elastic modulus of 424.8 GPa in the all samples. The microhardness (2200 HV0.05) of the duplex-treated sample was significantly higher than that of the only-coated (740 HV0.05) and nitrided (900 HV0.05) samples. The scratch tests revealed that the adhesion strength of the duplex-treated sample increased significantly due to a gradient-hardness support of the coating-nitrided layer interface.
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