Effect of substrate pulsed-direct current power frequency on tribological properties of a-C:H:Zr-x coatings

a-C:H:Zr-x coatings are deposited on high speed steel substrates using a closed field unbalanced magnetron sputtering system with pulsed-direct current power frequencies in the range 30 kHz to 110 kHz (the x in the term a-C:H:Zr-x is the frequency varied in the deposition process).The microstructure of the a-C:H:Zr-x coatings are varied as columnar, featureless and laminated shapes according to power frequency are increased, respectively. The coating hardness is various with the power frequency. Coatings a-C:H:Zr-70 and a-C:H:Zr-110 have the highest and lowest hardness values, i.e., 26 and 42 GPa. The tribological properties of the coatings are tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The experimental results reveal that the a-C:H:Zr-70 coating sliding against AISI 1045 steel cylinder and the a-C:H:Zr-110 coating sliding against AISI 52100 ball demonstrate particularly good tribological properties, namely a low wear depth, a low friction coefficient and a long lifetime.

► Pulsed-direct current power frequencies at the substrate varied from 30 to 110 kHz.
► a-C:H:Zr coating prepared at 70 kHz had the highest hardness (42 GPa).
► a-C:H:Zr coatings reduce wear depth compared with uncoated substrate.
► For all coatings, reduction by a factor of at least 10 against an AISI 1045 cylinder.
► For 50 to 110 kHz, reduction by a factor of more than 2 against an AISI 52100 ball.