Influence of gas mixture during N+ ion modification under plasma conditions on surface structure and mechanical properties of Al–Zn alloys

• Various N2/H2 ratios in plasma modifications of Al–Zn alloy are investigated.
• The N+ ion treatments of aluminum substrates were justified.
• SiCNH coatings on AA after N+ ion treatments can highly improve mechanical parameters.
• Modification process in RF CVD reactor was applied.

Aluminum, and particularly its alloys, are the materials of an increasing significance in construction and automotive industry due to the combination of their strength properties. However, their functionality is limited mainly because of the susceptibility on tribological wear. This paper presents the results of the study aimed at determining the optimum conditions of the process of alloy surface modification with N+ ions in the atmosphere of N2–H2, using the method of chemical precipitation from gaseous phase, combined with a discharge of a frequency of 13.56 MHz (radio frequency chemical vapor deposition). It was demonstrated that the process of Al–Zn alloy surface modification with nitrogen ions is a necessary prerequisite to obtain low-friction coatings (SiCNH in this case) characterized by a good and stable adhesion to the aluminum alloy substrate. The highest hardness is obtained in the case of SiCNH coating deposition process, preceded by the process of surface modification in plasma conditions, provided for N2 only (hardness 10.0 GPa) of the N2/H2 mixture (flow ratio 3/1, hardness 10.5 GPa). The surface of alloy combined with the obtained DLC (diamond-like carbon) layers, doped with N and Si atoms is characterized by ca. 30% decrease in the friction coefficient value (up to the 0.2 value) and ca. 25% decrease in the value of surface roughness (Ra, 6.5 nm), compared to unmodified substrates.

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