Characterization and Performance of TiAlN and TiN Coatings on Plasma-Nitrided AISI 4140 Steel

Abstract Steels can go through a duplex treatment process, consisting of depositing a physical vapor deposition (PVD) coating on plasma-nitrided substrates. The coating layer varies from 1.5 to 5 µm, depending on the application needs. The work's objective is to analyze the performance and evaluate the mechanical characteristics of titanium nitride (TiN) and titanium aluminum nitride (TiAlN) coatings deposited in AISI 4140 with quenched/tempered or plasma-nitrided treatment. Scanning electron microscopy/energy dispersive spectroscopy and X-ray diffraction performed the microstructural and chemical characterization of the duplex-treated samples. The mechanical properties were measured by performing nanohardness tests, allowing the extraction of hardness and elastic modulus out of the load/unload behavior of the samples, and the scratch test according to ASTM C1624-05 (2010), Standard Test Method for Adhesion Strength and Mechanical Failure Modes of Ceramic Coatings by Quantitative Singles Point Scratch Testing (Superseded), coupled with acoustic emission analysis, probed adhesion of the TiN and TiAlN coating on the steel substrates. Also, pin-on-disk tribological tests probed the wear resistance of the duplex-treated samples. It was found that the nitriding process increases the surface hardness and elastic modulus. The TiAlN coating has the highest load capacity with the least amount of wear. The adhesion of the TiAlN coatings is worse than TiN.