Phase composition and tribomechanical properties of Ti–B–C nanocomposite coatings prepared by magnetron sputtering

Abstract

Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB 2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti-B-C nanocomposite coatings were prepared by co-sputtering of graphite and TiB 2 targets. Varying the discharge power ratio applied to the graphite and TiB 2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and X-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB 2-like structure to a distorted TiB x C y ternary compound with increasing C concentration. Xray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiB x C y phase. A fitting analysis of the C1s XPS peak allowed to evaluate the relative amount of a-C and TiB x C y components. A drastic change in hardness (from 52 to 13 GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB 2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45 %. Raman observation of the wear tracks determined the presence of disordered sp 2-bonded carbon phase associated to the diminution of the friction level.

Tribocorrosion behavior of TiBxCy/a-C nanocomposite coating in strong oxidant disinfectant solutions

“…The wear rate for the coated specimens are one order of magnitude lower than AISI 316L, about 4 · 10 −6 mm 3 /Nm vs. 4 · 10 −5 mm 3 /Nm, respectively. These wear rates are in agreement with those reported in previous works in dry sliding wear tests [5][6][7], suggesting that the exposure to the oxidizing solution does not seem to influence greatly the wear rate. The good behavior shown by the coated specimens in comparison to the stainless steel suggests that TiB x C y /a-C coatings should be suitable for food processing and biomedical applications.…”

“…The higher COF value recorded for the TiB x C y /a-C (*) appears to point out some differences in comparison with the other two specimens. Values from 0.1-0.2 were also obtained on dry sliding of TiB x C y /a-C against WC-Co and 100Cr6 steel balls at loads of 1 and 5 N [5][6][7], indicating that these low values can also be achieved in wet conditions. The electrochemical noise measurements (potential and current fluctuations) recorded simultaneously during the sliding test for the TiB x C y /a-C coated specimens are shown in Fig.…”

“…The nanocomposites including amorphous carbon (a-C) as secondary phase are promising materials as protective coatings due to their appropriate combination of hardness along with additional interesting properties which are applicable to engineering applications such as low friction coefficient, wear resistance and toughness. In this line, TiB x C y /a-C nanocomposite coatings have shown a high degree of hardness, excellent wear resistance and low friction values under non-lubricated conditions [4][5][6][7]. For instance, in dry sliding tests performed against 100Cr6 steel and WC balls, a TiB x C y /a-C nanocomposite coating showed lower friction coefficient (0.2) than the TiB x C y compound without a-C phase in its structure (0.8) [5].…”

“…In this line, TiB x C y /a-C nanocomposite coatings have shown a high degree of hardness, excellent wear resistance and low friction values under non-lubricated conditions [4][5][6][7]. For instance, in dry sliding tests performed against 100Cr6 steel and WC balls, a TiB x C y /a-C nanocomposite coating showed lower friction coefficient (0.2) than the TiB x C y compound without a-C phase in its structure (0.8) [5]. From corrosion viewpoint, the requirements for effective protection include chemical inertness, high electrical resistance together with microstructural demands (high density, low microporosities and diffusion pathways, and good adhesion).…”

The electrical properties of coating obtained by vacuum arc deposition

“…The carrier concentration measured was 28 about n = 1 Á 10 22 cm À3 . The charge carriers' mobility varies between 10 and À7 and changes sign at 29 temperature about T = 225 K. and good electrical properties [1][2][3][4]. Electrical properties of the 39 coatings are not well investigated [4].…”