Investigation on the effects of plasma nitriding and air annealing post-treatments on the tribological properties of Arc-PVD CrN/CrTiSiN multilayer coatings

: This study investigated the effects of post-deposition treatments, including plasma nitriding and air annealing at 500 and 700 °C, on the structural, mechanical, and tribological properties of ∼5.6 μm thick multilayer CrN/CrTiSiN coatings deposited by Arc-PVD on AISI 304 stainless steel. XRD analysis revealed that the as-deposited coating consists mainly of CrN, Cr 2 N, and TiN phases, while annealing—particularly at 700 °C—promoted the formation of TiO 2 and Cr 2 O 3 oxides. Cross-sectional SEM observations confirmed that coating integrity was preserved after both plasma nitriding and annealing treatments, and all coatings exhibited excellent adhesion corresponding to the HF1 classification. The as-deposited coating exhibited a high hardness of 51.1 GPa, corresponding to a hardness approximately 14 times higher than that of the substrate. Post-treatment processes resulted in a gradual reduction in hardness to 45, 42, and 40 GPa for the plasma-nitrided coating and the coatings annealed at 500 °C and 700 °C, respectively. Under a normal load of 3 N, the wear depth remained below 1 μm, well within the coating thickness. However, at 5 N, coating degradation and third-body abrasion led to a significant increase in wear depth to values exceeding 20 μm. Except for the coating annealed at 500 °C, where the wear depth was below 5 μm.