Tribological Behaviour Of Diamond-like Carbon Coatings Research Articles

A Comparative Study in the Tribological Behavior of DLC Coatings Deposited by HiPIMS Technology with Positive Pulses

During the last few decades, diamond-like carbon (DLC) coatings were widely used for tribological applications, being an effective tool for improving the performance and the useful life of different machining tools. Despite its excellent properties, among which stand out a high hardness, a very low friction coefficient, and even an excellent wear resistance, one of the main drawbacks which limits its corresponding industrial applicability is the resultant adhesion in comparison with other commercially available deposition techniques. In this work, it is reported the tribological results of a scratch test, wear resistance, and nanoindentation of ta-C and WC:C DLC coatings deposited by means of a novel high-power impulse magnetron sputtering (HiPIMS) technology with “positive pulses”. The coatings were deposited on 1.2379 tool steel which is of a high interest due to its great and wide industrial applicability. Finally, experimental results showed a considerable improvement in the tribological properties such as wear resistance and adhesion of both types of DLC coatings. In addition, it was also observed that the role of doping with W enables a significant enhancement on the adhesion for extremely high critical loads in the scratch tests.

The effect of TiN and CrN interlayers on the tribological behavior of DLC coatings

The constant demand for new materials is coupled with a growing interest in thin coatings that will improve the performance-related parameters of an element without increasing its volume or changing the material structure. The aim of this study was to determine the influence of TiN and CrN interlayers on the tribological properties of a-C:H:W-type diamond-like carbon (DLC) coatings deposited on HS6-5-2 steel using the physical vapor deposition (PVD) method. The effect of the interlayers was established by analyzing the structure, surface topography, chemical composition and tribological properties of the DLC coatings. The coatings were tested under dry friction conditions at the nano-, micro- and macroscales. An atomic force microscope (AFM) was employed to analyze the coating surface topography and perform tribological testing at the nanoscale. The microscale tests were conducted using a microtribometer, while the macroscale tests were carried out with a ball-on-disc contact tester. The results confirmed that the two interlayers improved the tribological properties of components with DLC coatings.

Tribological behaviour of DLC coatings for sheet metal forming tools

Abstract Sheet metal forming processes usually involve a sliding contact between the blank and tool surfaces, thus requiring the use of lubricants to prevent severe tribological conditions at the tool–workpiece interface. However, improper lubrication policies may have a negative impact on the environment, due to the use of unhealthy degreasing agents to wash the formed parts. In recent years, the introduction of the diamond like carbon (DLC) coatings has represented an attractive solution for the development of dry or nearly-dry forming processes. To be effective, these coatings must strongly bond to the dies substrate in order to grant resistance to the abrasive and adhesive wear. Although many approaches for evaluating the tribological performances of such coatings can be found in the existing literature, they often suffer from limitations in reproducing the interface conditions typical of the industrial processes. The objective of the present research work is to investigate the tribological behaviour of DLC coatings applied to sheet-forming tools under process conditions compared to the ones experienced by the traditional coatings used in industry. Experimental values of the friction coefficient have been determined by means of strip drawing tests and the coatings wear and adhesion to the substrate have been investigated by means of pin-on-disk and scratch tests.

Towards the use of diamond-like carbon solid lubricant coatings in vacuum and space environments

Owing to the increasing demand in tribological performance for vacuum- and space-related applications, development of new solid lubricant coatings is necessary. Diamond-like carbon (DLC) coatings have been successfully used in many conventional mechanical applications to reduce both friction and wear. The potential use of these new solid lubricants under vacuum becomes then a critical question, which this article will attempt to address. DLC deposition, structure, and properties are first introduced to the reader. The exceptional tribological behaviour of DLC coatings is also discussed, in comparison with other tribological coatings. Attention is focused on the vacuum tribology of DLC films, pointing out the very low friction and wear that may be achieved with these materials. Phenomena accounting for establishment and lifetime of such low-friction regime are proposed. Finally, some open issues concerning vacuum- and space-related applications are discussed.

Tribological reactions between oil additives and DLC coatings for automotive applications

In the past, the development of modern engines and transmissions would have been impossible without advanced lubricant additive chemistry and proper lubricant formulation. Introduction of diamond and diamond-like carbon (DLC) coatings, especially metal doped DLC coatings, opens further possibilities in improving performance of engine and transmission components, which cannot longer be achieved only by lubricant design. However, the lack of knowledge on tribological behaviour of DLC coatings when lubricated with oils originally designed for metallic surfaces limit their use in practical applications. The results of the present investigation clearly show the existence of tribochemical reaction between metal doped DLC coatings (W-DLC) and S-based EP additives, while for a-C:H coatings additives had no influence. Furthermore, tribological behaviour of W-DLC coatings was found to be EP additive concentration and contact temperature dependant.