Modern Self-Lubricating Coatings for Automotive, Aviation and Spacecraft Industry

Abstract

A series of nanocomposite, self-lubricating coatings designed for dry friction at different temperatures based on amorphous carbon or amorphous MoS2 or amorphous MoO3 matrix was deposited by magnetron sputtering onto high-speed (HS) steel or Ti6Al4V alloy substrates and characterized with use of LM, SEM, TEM and HRTEM microscopy as well as with use of several other techniques. The nanocomposite nc-MeC/a-C(:H) carbon-based coatings (where Me=Cr or Ti or W) were composed of different nanocrystalline phases of a given transition metal of a size of several nanometers embedded in an amorphous hydrogenated or hydrogen-free carbon matrix. The nanocomposite MoS2(Ti,W) coatings were composed of Tiα or Wα or TiS2 nanocrystallites of 3 nm ÷ 10 nm diam. embedded in a semi-crystalline MoS2 matrix with MoS2 clusters of 3 nm÷8 nm diam. The magnetron sputtered MoO3 based coatings after deposition were composed of Ag nanocrystallites of 50 nm÷100 nm diam. embedded in an amorphous fractal-type matrix composed of MoO3 clusters of different size from very small to relatively great ones (not exceeding, however, 400 nm diam.). These amorphous clusters after 3 hours annealing in the ambient atmosphere under normal pressure at 300 °C transform into nanocrystalline MoO3 ones or after same annealing at 450 °C into crystalline silver molybdate Ag2MoO4 ones. The coatings preserve their resistance to wear and their low friction coefficient to approximately 250 °C in case of carbon-based coatings or to 350 °C in case of MoS2-based ones or to 550 °C in case of MoO3-based coatings. Several mechanical and tribological chracteristics of the coatings are given in the paper as well.

Thick Low-Friction nc-MeC/a-C Nanocomposite Coatings on Ti-6Al-4V Alloy: Microstructure and Tribological Properties in Sliding Contact with a Ball

“…The optimal process parameters were selected from the series of experiments published in earlier papers. [2,3,6,14] The process parameters during deposition of the nc-WC/a-C coating were as follows: the power of the magnetron with the W target was equal to 0.25 kW and that for the magnetrons with graphite targets was 2.1 kW (of each one of both) at an Ar pressure of 0.55 Pa. During deposition of the nc-TiC/a-C coating, the power of the magnetron with the Ti target amounted to 0.3 kW and for the magnetrons with graphite targets it was equal to 1.55 kW (for each one) at an Ar pressure of 0.4 Pa. To improve the coatings' adhesion to the substrate, at first a thin intermediate gradient layer was deposited. The composition of this layer changed from the pure metallic W or Ti and ended with a composition of the complete nc-WC/a-C or nc-TiC/a-C coating, respectively.…”

“…Several deposition processes of both coatings were performed for optimization of the deposition parameters. [6,14] The investigation of the coated alloy nano/microstructure was carried out with use of the scanning and transmission electron microscopy (SEM and TEM) as well as by X-ray diffractometry (XRD) and grazing incidence X-ray diffractometry (GIXRD). The SEM investigation was performed using a Zeiss NEON Ò CrossBeam 40EsB.…”

Failure modes of coatings on steel substrate

“…Subsequently the final MoS 2 (Ti,W) was deposited. During the whole deposition process the substrate bias was equal to −25 V. Microstructure and selected tribological properties of MoS 2 (Ti,W) coatings were described in [19] paper.…”