Abstract
Multilayers of Ti doped diamond-like carbon (Ti-DLC) coatings were deposited on aluminum alloys by filtered cathodic vacuum arc (FCVA) technology using C2H2 as a reactive gas. The effect of different Ti transition layer thicknesses on the structure, mechanical and adhesion properties of the coatings, was investigated by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation and a scratch tester. The results showed that the Ti transition layer could improve interfacial transition between the coating and the substrate, which was beneficial in obtaining excellent adhesion of the coatings. The Ti transition layer thickness had no significant influence on the composition and structure of the coatings, whereas it affected the distortion of the sp2-C bond angle and length. Nanoindentation and scratch test results indicated that the mechanical and adhesion properties of the Ti-DLC coatings depended on the Ti transition layer thickness. The Ti transition layer proved favorable in decreasing the residual compressive stress of the coating. As the Ti transition layer thickness increased, the hardness value of the coating gradually decreased. However, its elastic modulus and adhesion exhibited an initial decrease followed by an increasing fluctuation. Among them, the Ti-DLC coating with a Ti transition layer thickness of 1.1 μm exhibited superior mechanical properties.
Highlights
Aluminum (Al) alloys have wide applications in the aviation, aerospace, electronics, automobile and other industries due to advantages such as low density, high specific strength and excellent corrosion resistance [1,2,3]
When the C2 H2 of 99.8% purity was injected in the vacuum chamber and collided with the ionized Ti plasma, new cations were formed which were available for the deposition of Ti doped diamond-like carbon (Ti-diamond-like carbon (DLC)) coatings
The Ti layer and the Ti-DLC layer can be clearly delineated by a scratch tester (Revetest® RST3, Anton Pear GmbH, Shanghai, China)
Summary
Aluminum (Al) alloys have wide applications in the aviation, aerospace, electronics, automobile and other industries due to advantages such as low density, high specific strength and excellent corrosion resistance [1,2,3]. It is impossible to obtain excellent adhesion property by only introducing metal elements into DLC coatings, owing to the mismatch in the thermal expansion coefficient and the mechanical properties of the DLC coatings and the Al alloys. Another strategy for effectively improving the adhesion of the DLC coating is to add transition or buffer layers, such as Ti, Cr, Al, Si, TiC, TiN, complex Ti/TiN, Ti/TiC/TiN, AlN/Ti/TiN, and so on [13,14,15,16]. Technology, and studied the effect of the Ti transition layer thickness on the structure and mechanical properties of the Ti-DLC coatings to obtain an optimum Ti transition layer thickness
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