The tribological properties of nanometre carbon films prepared by plasma-based ion implantation at various implanting voltages

Abstract

About 30 nm thick nanometre carbon films have been prepared on Si wafers by plasma-based ion implantation at various implanting voltages. The ball-on-disc sliding friction experiments show that the tribological properties of these carbon films are in good agreement with the corresponding structure characteristics which strongly depend on the implanting voltage. These structure characteristics include the film roughness, the film thickness, the C–Si transition layer between the carbon film and the Si substrate and the sp3/sp2 ratio. As the implanting voltage increases, the roughness and the thickness decrease, the C–Si transition layer thickens and the sp3/sp2 ratio first increases to the maximum value at about 30 kV and then decreases. 3 kV and below correspond to bad tribological properties owing to polymer-like carbon (PLC) film and no C–Si transition layer with poor adhesion to the Si substrate. When the implanting voltage increases to over 3 kV, a C–Si transition layer is gradually formed and thickens with increasing adhesion, and the PLC film is gradually turned into a diamond-like carbon (DLC) film, and hence the tribological properties are gradually improved and reach the best values at 30 kV. 10–50 kV correspond to two orders of increase in wear life, close to zero volume wear rate, but about 0.3 friction coefficient at 0.1 N applied load. With the increase in the applied load, the wear life and the friction coefficient decrease and the wear rate increases. For Si wafers coated with the DLC films at 30 kV, in the range of 0.5–1 N, there is an appropriate value corresponding to the wear life of above 18 000 s, friction coefficient of about 0.1 and wear rate of 10−9 mm3 N−1 m−1 level. Additionally, the wear mechanism is discussed.

Thick gradient layers prepared by plasma-based ion implantation on 2024 aluminium alloy

“…The stress is mostly due to the intrinsic stress of the DLC film. The stress is in the range 0.7-1.4 GPa from GL1 to GL5, which is close to those of the thin PBII-DLC film on single crystal Si wafers [6,7] and much lower than those of the DLC films prepared by other methods [20,25,26]. This is related to the good composition and structure gradients of the gradient layers.…”

“…However, the AlN layer, which is often less than 0.3 µm thick, is difficult to eliminate the effect of Al and its alloy and hence difficult to satisfy the actual requirements. As excellent wear-resistant films, diamondlike carbon (DLC) films have been significantly attractive in tribological applications due to their high hardness and elastic modulus, low friction coefficient and wear rate [4][5][6][7]. Unfortunately, little work has been done on the DLC film on soft substrates such as Al alloys and titanium alloys because soft substrates may not be able to provide adequate support for the hard DLC films, adversely affecting their tribological performance and durability owing to considerable structure and property difference between the soft substrates and the DLC film.…”

“…Fortunately, plasma-based ion implantation (PBII) can overcome the disadvantage because its alternate deposition and implantation can easily form a transition layer, which displays the composition and structure gradient, to connect the prepared layer and the substrate [6,7,9,10]. To the best of our knowledge, there are few reports of studies on preparing more than a 1 µm thick layer by PBII; thus this paper deals with the preparation of thick gradient layers by PBII on the 2024 Al alloy and studies the topography, structure, hardness, stress and tribological properties.…”

Tribological performance of ultrathin diamond-like carbon films prepared by plasma-based ion implantation

“…Diamond-like carbon (DLC) films have widespread applications such as protective coatings in optical windows, magnetic storage discs, car parts, biomedical coatings, micro-electromechanical systems and devices therein [1] owing to their excellent tribological properties and other outstanding properties [2][3][4][5]. In particular, DLC films have served as a type of ideal lubricating and protective film due to unique antifriction and wear-resistance characteristics when normal oil lubrications and protective coatings are not suitable for some special fields where two or more mobile devices show micrometre, even nanometre, spaces and need smooth, compact, adhesive and wear-resistant thin solid films [6][7][8][9][10][11][12][13].…”

“…obtained by PBII are strongly dependent on the process parameters such as implanting voltage [9] and working gases [12]. As another prominent parameter, the implanting time, is proportional to the DLC film thickness and plays a dominant role in tribological properties [5], and hence is closely associated with the film applications.…”