Effects of working pressure on structure and properties of Al-containing amorphous carbon films prepared by high-power impulse magnetron sputtering

Al-containing amorphous carbon (a-C:Al) films were fabricated under different working pressures by high-power impulse magnetron sputtering. Morphologies, microstructure and chemical composition of a-C:Al films were characterized by scanning electron microscopy, atomic force microscope, X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. Mechanical properties and tribological behavior of a-C:Al films were investigated by film stress tester, nano-indentation, scratch tester, ball-on-disk tribometer and 3D surface profiler. Results showed that atomic composition of Al in a-C:Al films was about 5%, independent of working pressure. The prepared films have smooth surfaces with Ra of 2.22 nm–5.89 nm. Typical amorphous structures could be observed in a-C:Al films and sp3 content could be governed by changing working pressures. Al existed as an oxide of aluminum in carbon matrix. There was a notable negative correlation between internal stress and sp3-C content. All samples manifested good adhesion strength to substrates with critical loads beyond 70 N. Wear rates were in 10−8 mm3 N−1 m−1 order of magnitude and had the same changing trend with H/E as working pressure rose from 0.3 Pa to 0.6 Pa. a-C:Al film prepared at 0.4 Pa has the best wear resistance with a wear rate of 4.38 × 10−8 mm3 N−1 m−1.