Influence of chemical composition of Ti/TiC/a-C:H coatings deposited on 7075 aluminum alloy on their selected mechanical properties

• The possibility of depositing a highly adhesive carbon coating in a two-step aging treatment of the substrate has been proven.
• The possibility to control the disordered carbon by change of the polarization potential has been proven.
• The impact of the disordered carbon on selected mechanical properties of the carbon coating has been defined.

This paper presents the results of research on the deposition of gradient antiwear Ti/TiC/a-C:H coatings on Al–Zn alloys (7075 series) using a hybrid method Radio Frequency Plasma Assisted Chemical Vapor Deposition (RF PACVD). In order to eliminate the over-aging effect of the aluminum substrate it was subjected to T6I6 treatment. The alloy has been strengthened by precipitation and a first aging process, at a temperature of 813 K for 6 h and at 430 K for 1 h, respectively. Synthesis of the gradient coatings on 7075 aluminum alloy was performed simultaneously during the second stage of the aging process at 390 K for 6.5 h. It has been proved that the change in the substrate bias potential in the range of 150–600 V (constant value for each process) influences the mechanical properties of the resulting coatings (hardness in the range 10–19 GPa and adhesion to the substrate from 16 up to 33 mN).It has been proved in this case that during the substrate aging process it is possible to control the contribution of disordered carbon. Its value (calculated as D/G area ratio) in the range of 0.75 allows obtaining coatings with a coefficient of friction of about 0.05 (Al2O3 or Si3N4 counterparts, 5 N load) and wear rates of about 4.4 ∗ 10− 5 mm3/Nm, which due to their chemical structure behaves as solid lubricant in the friction pair.