Hard yet tough CrN/Si3N4 multilayer coatings deposited by the combined deep oscillation magnetron sputtering and pulsed dc magnetron sputtering

Abstract

Hard yet tough coatings with simultaneously high hardness and toughness represent a new class of high-performance coatings, which are vital for tribological applications due to the enhanced surface/interface properties. In this work, CrN/Si3N4 multilayer coatings with various Si content were reactively deposited by the combined deep oscillation magnetron sputtering and pulsed dc magnetron sputtering. The as-deposited coatings exhibit smooth surface morphology, well-defined nc-CrN/a-Si3N4 interfaces, uniform thickness and highly dense architecture. Microstructure evolution is induced by Si content changing from scaly nanocolumnar to densely packed fibrous grains to tapered crystallites. These features allow the achievement of the increased properties in terms of high hardness of 30.6 GPa, H/E* of 0.099, H3/E*2 of 0.387, elastic recover We of 58.5% and fracture toughness KIC of 3.69 MPa·m1/2. Hard yet tough CrN/Si3N4 multilayer coatings show excellent tribological properties by enhanced cooperative deformability through energy dissipation and stress relaxation at well-arranged nc-CrN/a-Si3N4 interfaces to reduce crack initiation and propagation, and adhesion failure, thanks to the enhanced H, H/E*, H3/E*2, We and KIC. Meanwhile, under limited normal load conditions, uniform tribolayers (Cr2O3, FeO(OH), Fe2O3 and Fe3O4) caused by tribochemical reaction on the worn surface also act to make contributions towards reducing friction and wear as a lubricant.