Influence of substrate bias on the properties of CrAlN wear-resistant coating prepared by arc/magnetron composite technology

CrAlN coatings were deposited onto stainless steel substrates using mid-frequency magnetron sputtering and arc-ion plating. The research comprehensively analyzes how varying substrate bias voltage influences the microstructural morphology, mechanical properties, and frictional behavior of the coatings using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, nanoindentation, scratch test, and friction and wear tests. As the substrate bias voltage increases, the coated surface evolves from a porous with large grains to a dense and smooth state. At a bias of −60 V, the coating exhibited minimal surface particles and pores, resulting in the best overall surface quality and excellent adhesion to the substate. Moreover, all coatings displayed the composite properties of metal and metal nitride mixtures. In addition, substrate bias, a key process parameter, was found to affect particle activity and sputtering yield, thereby modulating element distribution in the coating and coating properties. The CrN, AlN, and CrAlN phases with face-centered cubic structures were observed by XRD. In particular, the addition of Al elements caused the diffraction peak of the CrAlN phase to shift to higher angles. At a substrate bias of −30 V, the coating exhibited multiple strong diffraction peaks. When the substrate bias was −60 V, the coating preferentially grew along the (200) crystal plane. However, an excessive substrate bias (−150 V) exacerbated the secondary sputtering effect during deposition, resulting in a decreased deposition rate, lattice relaxation, and recrystallization. Coatings prepared with different bias voltages consistently exhibited compressive stress, which increases with the bias voltage and, to a certain extent, improves the mechanical properties. The combined effect of growth and thermal stresses results in a higher residual stress for coatings prepared at a −150 V substrate bias. Increasing the substrate bias initially enhanced the hardness and elastic modulus of the coating; however, these properties eventually declined. The peak hardness at a −60 V substrate bias is attributed to lattice distortion, the Al solid solution in the CrN lattice, and internal stresses. Moreover, coatings at this bias level exhibited better elastic recovery and plastic deformation resistance. The friction coefficient increases rapidly over time before stabilizing, with the lowest average friction coefficient (0.75). At this bias −60 V, the coating demonstrated a low wear rate, while a higher substrate bias led to severe abrasive wear. Tuning the substrate bias voltage, allowed for effectively optimizing the microstructure, mechanical properties, frictional behavior, and wear resistance of CrAlN coatings. Notably, CrAlN coatings prepared at a substrate bias of −60 V exhibited exceptional mechanical properties and wear resistance, providing a crucial theoretical and experimental foundation for enhancing their performance in practical applications.