Effects of intermediate layers on the tribological behavior of DLC coated 2024 aluminum alloy

DLC coated 2024 aluminum alloy samples having four different intermediate layers prepared by different plasma-based ion implantation modes. The composition and structures of DLC coated samples were investigated by X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy and glancing angle X-ray diffraction (GXRD). Knoop micro-hardness and nano-hardness of the layers had been measured too. The tribological behaviors of these samples were investigated by ball on disk frictional tester and scanning electron microscopy (SEM). Results show that the stable friction coefficients of these four samples are nearly same and about 0.1, but the sliding cycles of holding stable friction coefficient are different, they increase according to the order of samples (a)–(d) sequentially. For these four samples, whether the loading was 1 or 20 N, the stable friction coefficient is nearly same, but the sliding cycles of holding stable friction coefficient are different, while the cycles of holding stable friction coefficient as loading 20 N are less than as loading 1 N for same sample. The wear rate of the samples decreases according to the order of samples (a)–(d) sequentially. The SEM morphologies of the worn tracks are dependent on the intermediate layer structures and friction test conditions, the characters of the wear are rubbing, abrasive wear and delamination wear, but for samples (a) and (b) a slight adhesive wear appears as loading 20 N.