A study of structural and wear properties of PACVD deposited a-C:H thin films for application as protective layers on Al alloys

Due to the high strength-to-weight ratio, aluminum alloys are commonly used materials in aircraft and automotive industries. However, the low hardness and wear resistance and high friction coefficient limit their applications. In this study, we deposited a-C:H thin films on 7075 Al alloy substrates without an interlayer by direct current PACVD method. Negative substrate bias was varied to improve the surface mechanical properties. We obtained smooth, homogenous, and well adhered up to 28m thick a-C:H layers on the Al alloy substrates. The structural and mechanical properties were analyzed using Raman spectroscopy, SEM, nanoindentation and Pin-on-disc test. Raman spectroscopy showed a higher content of trans(CH)(x) within the films deposited with low bias and increased sp(2) bonding for higher bias depositions. Adhesion test has shown the adhesion grade HF1 to HF4. Coefficient of friction was measured in the range 0.05-0.15 and wear rates of a-C:H covered samples were significantly reduced in comparison to uncovered substrates. The obtained results show a promising potential of the a-C:H as wear resistant coatings for the 7075 Al alloy.