Abstract
TiB2/ZrO2 multilayers with different modulation ratios (at a fixed modulation period of 50 nm) ranging from 2:1 to 6:1 were deposited by magnetron sputtering. The oxidation behavior of the as-deposited multilayers was investigated at 600 °C in air. The microstructures, mechanical properties, and oxidation resistance of the multilayers were analyzed and compared. The results indicate that discontinuous oxidation retarded the inward diffusion of oxygen and the outward diffusion of metallic components. The formation of dense (Ti, B)-oxide scale and internally inserted ZrO2 layers in the TiB2/ZrO2 multilayers enhanced the oxidation resistance. Moreover, the oxidation resistance of the multilayers increased as modulation ratio decreased. The hardness and elastic modulus of the TiB2/ZrO2 multilayers were maximized (23.9 and 303.1 GPa, respectively) at the modulation ratio of 6:1. After annealing, the formation of thick ZrO2 layers did not lead to sustained increases in hardness. The maximum hardness and elastic modulus were obtained at the critical modulation ratio of 4:1, and good adhesion strength with the substrate was also observed. The oxidation mechanism and experimental results demonstrate that controlling the modulation ratio of multilayers can produce synergetic enhancements in the oxidation resistance and mechanical properties of multilayers after high-temperature oxidation.
Highlights
The development of industry has generated increased demand for coatings with outstanding mechanical properties and oxidation resistance at high temperature for use in cutting tools and microelectronics [1,2]
The oxidation process was conducted in air inside a chamber furnace at diffraction peaks indicate a hexagonal phase of TiB2 and a monoclinic phase of ZrO2 (m-ZrO2)
The cross-sectional SEM images of the TiB2 /ZrO2 multilayers indicate that the compact (Ti, B)-oxide scale became thicker as TiB2 monolayers and TiB2/ZrO2 (tTiB2) :tZrO2 increased
Summary
The development of industry has generated increased demand for coatings with outstanding mechanical properties and oxidation resistance at high temperature for use in cutting tools and microelectronics [1,2]. Multilayers prepared by magnetron sputtering combine the advantages of the different constituent materials and have better performance and microstructure compared to single layers of their respective components due to the superhardness effect, quantum effects, and macro-tunneling effects between the nanolayers [18,19,20,21,22]. In addition to resulting in excellent mechanical properties, the formation of multilayer structures can improve the oxidation resistance at high temperatures through limited intermixing [23,24,25]. TiB2 has a higher hardness (~34.0 GPa) than ZrO2 (~11.8 GPa), and can effectively improve the mechanical properties of multilayers. The relationships between microstructural features, chemical components, oxidation resistance, and mechanical performance were established in order to aid practical applications of multilayers in machining
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