High-Temperature Tribological Performance of Al2O3/a-C:H:Si Coating in Ambient Air

Vitali Podgursky,Mati Danilson,Mart Viljus,Taavi Raadik,Jan Kluson,Andrei Bogatov,Jozef Sondor,Andreas Lümkemann,Maxim Yashin,Fjodor Sergejev,Asad Alamgir,Taivo Jõgiaas

doi:10.3390/coatings11050495

Abstract

The study investigates thermal stability and high temperature tribological performance of a-C:H:Si diamond-like carbon (DLC) coating. A thin alumina layer was deposited on top of the a-C:H:Si coating to improve the tribological performance at high temperatures. The a-C:H:Si coating and alumina layer were prepared using plasma-activated chemical vapour deposition and atomic layer deposition, respectively. Raman and X-ray photoelectron spectroscopy were used to investigate the structures and chemical compositions of the specimens. The D and G Raman peaks due to sp2 bonding and the peaks corresponding to the trans-polyacetylene (t-Pa) and sp bonded chains were identified in the Raman spectra of the a-C:H:Si coating. Ball-on-disc sliding tests were carried out at room temperature and 400 °C using Si3N4 balls as counter bodies. The a-C:H:Si coating failed catastrophically in sliding tests at 400 °C; however, a repeatable and reproducible regime of sliding with a low coefficient of friction was observed for the Al2O3/a-C:H:Si coating at the same temperature. The presence of the alumina layer and high stress and temperature caused structural changes in the bulk a-C:H:Si and top layers located near the contact area, leading to the modification of the contact conditions, delivering of extra oxygen into the contact area, reduction of hydrogen effusion, and suppression of the atmospheric oxidation.

Highlights

The minimisation of heat generation, friction, and wear demand in industry is an essential issue for sustainable development [1]
The alumina layer grew conformally, that is, it resembled the morphology of the a-C:H:Si surface
After 180 min sliding tests at room temperature (RT), a wider and shallower wear scar was found on the Al2 O3 /a-C:H:Si coating in contrast to the a-C:H:Si coating

Summary

Introduction

The minimisation of heat generation, friction, and wear demand in industry is an essential issue for sustainable development [1]. [1,2]) owing to their low coefficient of friction (COF) for different types of friction pairs, good mechanical properties, and chemical inertness. The challenge is that these properties should be retained during intensive use of such coatings under aggressive conditions (temperature, atmosphere, irradiation, etc.). The tribological performance of carbon-based coatings is sensitive to their properties (hardness, internal stress, adhesion, thermal stability, oxidation resistance, surface roughness, etc.) and test conditions (sliding regimes, atmosphere, temperature, etc.). In addition to the preparation of carbon-based coatings using different deposition techniques, there are some straightforward approaches to modifying the structure of the coatings. The surface and bulk properties can be changed by doping, annealing, and irradiation

Methods

Discussion

Conclusion