Microstructure, mechanical and adhesive properties of CrN/CrTiAlSiN/WCrTiAlN multilayer coatings deposited on nitrided AISI 4140 steel

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 e-Fe 2-3 N and γ′-Fe 4 N 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 HV 0.05 ) of the duplex-treated sample was significantly higher than that of the only-coated (740 HV 0.05 ) and nitrided (900 HV 0.05 ) 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.