Tribological behavior of hydrogenated W-C/a-C:H coatings deposited by three different sputtering techniques

Abstract

The evolution of structure, mechanical properties and friction behavior of DC magnetron sputtered (DCMS), high power impulse magnetron sputtered (HiPIMS) and high target utilization sputtered (HiTUS) W-C:H coatings was investigated as a function of the addition of acetylene and hydrogen into Ar atmosphere. The gradual addition of reactive gases caused a transition from PVD toward hybrid PVD-PECVD and even PECVD dominant processes. The coating structure evolved from nanocrystalline toward nanocomposite and amorphous structure with the increase of acetylene addition. Deposition rates in all techniques increased linearly with the increase of acetylene flow until certain saturation limit due to the limited energy available for acetylene fragmentation during hybrid PVD-PECVD deposition. Hardness and coefficient of friction in DCMS and HiTUS W-C:H coatings deposited in this regime followed standard congruent tendencies whereas PECVD dominated deposition process produced coatings with different dependencies. In contrary, HiPIMS W-C:H coatings showed low sensitivity to the influence of acetylene and hydrogen additions. Lower coefficients of friction (<0.1) and moderate hardness (around 20 GPa) of HiPIMS W-C:H coatings over a wide range of acetylene additions seem to be a principal advantage of HiPIMS compared to DCMS and HiTUS techniques in this class of coatings. Keywords: W-C:H coatings, DC magnetron sputtering (DCMS), high power impulse magnetron sputtering (HiPIMS), high target utilization sputtering (HiTUS), hardness, coefficient of friction.

Tribological performance of Nb-C thin films prepared by DC and HiPIMS

“…The hardness values range from 11 to 20 GPa, in good agreement with the values presented by other authors [8,9] for NbCx based coatings (16)(17)(18)(19)(20)(21)(22)(23). The reduced Young´s modulus did not change greatly among the samples, showing a value of around 220 GPa.…”

“…A similar trend with the increasing carbon content was observed for NbCx-based nanocomposites prepared by reactive and non-reactive magnetron sputtering PVD [8,9] and TiC/a-C nanocomposite coatings comparing HiPIMS and DC techniques [11]. Previous papers have reported a higher film densification and a better functionality using HiPIMS [12,13]; however, the lower deposition rates, the preservation of the growth [14,15], and the non significant improvement of the tribomechanical properties on WC/a-C:H [16] and TiC/a-C:H [11] have been highlighted by other authors.…”

Hardness of Hybrid PVD-Pecvd W-C:h Coatings vs. Substrate Type

“…A set of 14 coatings with variable additions of C 2 H 2 precursor (0, 2, 4, 6, 8 sccm) and (0, 5, 10, 20 sccm) into Ar atmosphere was prepared for the study. The thicknesses of the coatings were in the range from 0.7 µm up to almost 3 µm depending on the amount of precursor gas additions [15][16][17][18]. The nanoindentation tests were carried out on a nanoindenter (model G200, Agilent, USA) using a diamond Berkovich tip in CSM mode with the preset maximum penetration depth of 1000 nm, strain rate of 0.05 s −1 , frequency of 45 Hz and amplitude of 2 nm on a set of 16 indents.…”

“…It is known from earlier works on DC magnetron sputtered and HiPIMS W-C:H coatings [17,18] that the structure of the PVD coatings without additions of acetylene may vary from nano-columnar to nanocrystalline, which resulted in the variations of hardness from 34 GPa to 28 GPa, respectively. The additions of acetylene caused gradual increase of the content of hydrogenated free carbon phase and a transition from nanocomposite to amorphous structure accompanied by a decrease of hardness [16][17][18]. The substrate itself may also play significant role in the formation of the coating structure and its morphology [15].…”

Tribochemistry of Transfer Layer Evolution during Friction in HiPIMS W-C and W-C:H Coatings in Humid Oxidizing and Dry Inert Atmospheres

“…Hydrogen-free W-C coatings are usually produced by conventional PVD methods, mostly by co-sputtering from W and C targets [13]. The carbon-to-tungsten (carbide) ratio in the coatings can be controlled by the power on each magnetron, which can be driven by either direct current (DCMS), RF (RFMS), high-power impulse (HiPIMS) magnetron sputtering or even by high target utilization sputtering (HiTUS) [7,[13][14][15][16][17]. In contrast, hydrogenated W-C:H coatings require so-called "hybrid PVD-PECVD" processes when WC (or W) is supplied by the abovementioned magnetron sputtering, whereas the hydrogenated carbon originates from simultaneous plasma polymerization reactions of reactive gaseous precursors in the plasma of Ar sputtering atmosphere [11,14,15,[17][18][19].…”