Structural modification and tribological behavior improvement of solid lubricating WSe x coatings during pulsed laser deposition in buffer He-Gas

Abstract

Thin film, solid lubricating WSe x coatings were deposited at room temperature on a steel substrate with a titanium underlayer by pulsed laser deposition (PLD). Two modes of PLD were investigated, i.e., the PLD under vacuum conditions and the PLD in a buffer gas (helium) at a pressure of 2-10 Pa. Gas was used to slow down the laser induced atomic flux and to modify thus the conditions of the coatings growth. At a pressure ~8 Pa, gas reduced the effectiveness of Se preferential sputtering by atomic flux, which resulted in the formation of coatings with a stoichiometric composition (x ≈ 2). The structure of the coatings was char acterized by a greater degree of the perfect organization of atoms in the nanophase laminar packaging and reduced internal stresses. Studies by the ball on disk tests in humid air showed that the modification of the structure and the chemical composition of the coatings had a significant effect on their tribological behavior. Vacuum deposited coatings fractured relatively quickly due to the cracking and delamination from the sub strate surface along the sliding track. When the coatings deposited in helium were tested, wear by layer by layer removal was dominant, so the adhesive fracture was only observed in the local parts of the track. The simulation of the laser vapor deposition in the vacuum and in the buffer gas was performed. Likely factors that improve the tribological properties of the coating during deposition in the buffer gas were disclosed.

Structure and tribological behavior of nanocomposite C-Ti-WSe x coatings

“…We note that the contrast of the amorphous matrix of the C-Ti-WSe x films in the TEM examinations is much similar to the contrast of the unalloyed WSe x films found in [10]. This contrast includes bright and dark filamentous fragments typical of the laminar structure of TMD materials.…”

“…The coefficient of the wear of the ball does not The examination of the wear scar on the ball after sliding against the composite coating shows that wear products stick to the counterface and form a dense tri bofilm on the leading side of the ball (from the side of the direction of motion). A similar pattern of changes on the counterface was observed in [10] after the tri botests of unalloyed WSe x coatings. After friction against the a C(Ti) coating, friable wear products appear, and no cushion of wear products is formed on the counterface.…”

“…We note that a comparison of the wear resistances of the unalloyed WSe x coatings and the composite C-Ti-WSe x coat ings shows a noticeable advantage of the composite coatings. Even at decreased air humidity, the coefficient of the wear of the WSe x coatings is approximately two times higher than that of the composite coatings [10].…”

Microstructures and properties of titanium nitride films prepared by pulsed laser deposition at different substrate temperatures

“…It is a kind of physical vapor deposition technique which has controllable deposition parameters, including laser energy, repetition rate, substrate temperature, deposition time, gas flux as well as target-substrate distance. Growth conditions such as deposition atmosphere [18,19], repetition rate [20] and substrate temperature [21][22][23] can hugely modify the crystalline quality, microstructure, thickness, surface morphology and mechanical properties of films, which have been investigated in great detail. In previous study, Lippert [21] used the PLD technique to fabricate the yttria-stabilized zirconia (YSZ) films at room and high temperatures, which exhibited a uniform isotropic structure in the case of room temperature deposition and an oriented columnar growth at substantially higher substrate temperatures of 400-700 • C. Matei [23] fabricated the vanadium nitride films at room temperature and 500 • C by the PLD technique.…”