Aluminum alloys are lightweight materials with a range of excellent properties and extensive applications. Due to their high specific strength, exceptional low-temperature toughness, corrosion resistance, and ease of processing, aluminum alloys have promising potential in fields such as aerospace and transportation. However, the low hardness and poor wear resistance of aluminum alloys can significantly impact the longevity and safe operation of some high-performance equipment. Diamond-like carbon (DLC) coatings exhibit high hardness, wear resistance, and chemical inertness, making them ideal wear-resistant protective coatings for aluminum alloy components. Nevertheless, the differences in mechanical properties between aluminum alloys and DLC coatings can cause the Al/DLC alloy system to face changing loads under frictional operating conditions, which can lead to DLC failure. In this study, 1-μm thick DLC coatings were prepared using a linear ion beam. Titanium transition layers with varying structures were deposited by adjusting the duty ratio (2%–10%) of high-power pulsed magnetron sputtering technology (HiPIMS). The effects of different interface structures of transition layers on the mechanical and friction properties of the Al/DLC system were systematically investigated. A coating prepared using the DC magnetron sputtering technique served as a control group. SEM and TEM were used to observe the surface and cross-sectional morphology of the coatings. Raman spectroscopy was employed to characterize the bonding structure of DLC. The changes in coating surface roughness were determined using AFM. Nano-indentation tests provided the hardness and elastic modulus of the coatings. The tribological properties of the coatings were assessed using ball-disk friction equipment. Results showed that the bonding structure of DLC was not affected by the titanium transition layer structure. All titanium layers exhibited a distinct columnar structure. As the duty ratio increased, the decrease in peak power led to a reduction in titanium ion energy, and all titanium layers were oriented from (100) to (002) due to surface energy minimization. The roughness of the top layer DLC changed as a result of the titanium layer structure (Ra = 10.6–14.5 nm). Scratch tests revealed that samples prepared via HiPIMS (8.4–8.6 N) demonstrated higher adhesion strength than those prepared by DC (7.0 N). Furthermore, the change in duty ratio had no significant effect on the adhesion of HiPIMS samples. Friction experiments showed that the average friction coefficient of the DC sample was 0.15, while that of the HiPIMS sample was 0.07. Different amounts of amorphous carbon transfer films were observed adhering to the Al2O3 ball. Compared with the sample prepared via DC, HiPiMS can simultaneously reduce the grain size and increase the proportion of (002) plane, providing the coating with a stronger bearing capacity and significantly improving its mechanical and tribological properties (samples with a duty ratio of 8% exhibited a hardness of approximately 29.9 GPa, a modulus of 220.6 GPa, H/E and H3/E2 values of 0.136 and 0.550 GPa, respectively, and the lowest friction coefficient and wear rate of 0.07 and 4.5×10−7 mm3/(N·m), respectively). The failure modes of all coatings during friction testing were similar, consisting of tensile cracks and flake spalling due to frictional shear stress. Trenches parallel to the loading direction were observed in the friction traces. Thus, depositing a titanium transition layer with a low (100) preferred orientation and dense structure is key to preparing high-performance Ti/DLC coatings on aluminum alloys. This approach offers a novel solution to address the issue of easy peeling of wear-resistant coatings on aluminum alloy components. © 2023 Chinese Mechanical Engineering Society. All rights reserved.
