Percorrer por autor "Bondarev, Andrey"
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- Mutual promotion on the mechanical and tribological properties of the nacre-like self-lubricant film designed for demanding green tribological applicationsPublication . Hongbo, Ju; Luan, Jing; Wang, Yiping; Bondarev, Andrey; Evaristo, Manuel; Geng, Yaoxiang; Xu, Junhua; Cavaleiro, Albano; Fernandes, Filipe; Fernandes, FilipeThe inverse relationship between the tribological and mechanical properties of environmentally friendly self-lubricant films, induced by the addition of soft lubricant agents that can diffuse quickly at elevated temperatures, has hindered the widespread use of these materials in industrial applications. This paper took this challenge to break through the above established relationship by developing novel nacre-like multilayered Mo2N–SiNx/Ag–SiNx self-lubricant films via an radio frequency (RF) magnetron sputtering system for real applications where harsh conditions at elevated temperatures exist. The multilayered films, deposited by alternating deposition of Mo2N–SiNx and Ag–SiNx modulation layers, exhibited three phases of face-centered cubic (fcc) Mo2N, fcc Ag and SiNx, where SiNx encapsulated the nano-crystalline Mo2N and Ag phases in each layer to successfully induce a “brick and mortar” nacre-like microstructure (in the area without the coherent structure). The epitaxy growth of the Ag–SiNx layers with thickness below 6 nm on the Mo2N template resulted in an extraordinary increase in both the hardness and elastic modulus, which was able to prevent severe degradation of the mechanical properties caused by the addition of Ag. The room-temperature anti-friction property could be enhanced by increasing the Ag–SiNx layer thickness due to the excellent lubricant nature of Ag, which acts in synergy with Mo2N, while the wear rate below 4×10−8 mm3/(N·mm) was due to the high mechanical strength. The tribological properties at 600 °C also benefited from the interlocked multilayered architecture, which allowed an extreme low friction coefficient of ~0.12 and a negligible wear rate (WR). This behavior was attributed to the synergism between the lubricant action of Ag and Mo2N and the tribo-phase transformation from Ag2Mo4O13 to Ag2MoO4.
- TEM study of the oxidation resistance and diffusion processes in a multilayered TiSiN/TiN(Ag) coating designed for tribological applicationsPublication . Bondarev, Andrey; Al-Rjoub, Abbas; Bin Yaqub, Talha; Polcar, Tomas; Fernandes, FilipeThis work investigates the structure evolution of a multilayered TiSiN/TiN(Ag) coating with heating, oxide scale growth, diffusion processes occurring during oxidation, and changes in the structure and chemical composition of the non-oxidized zone. The coatings have a multilayered structure with a bilayer periodic thickness of ~40 nm. The TiN(Ag) layer consists of fcc TiN and Ag crystalline phases, where Ag nanocrystallites are homogenously distributed at the TiN grain boundaries. The TiSiN layer consists of fcc Ti–Si–N solid solution grains and an amorphous a-SiNx phase which segregates at the Ti–Si–N grain boundaries. In-situ hot-XRD analysis shows that the first signs of oxidation occur at 800 ◦C, when rutile-TiO2 starts to form. The oxidized part of the coating is Ag depleted, except the top layer terminating the structure, which contains some 1–3 nm Ag clusters. Ag diffuses towards the surface from oxidized zones. The cross-sectional analysis also shows no signs of recrystallization and structural changes, except for stress relaxation in the non-oxidized part after annealing at 800 ◦C. No Ag redistribution or diffusion is found in the non-oxidized part, even close to the interface with the oxide layer, which suggest effectiveness of the multilayered design to mitigate uncontrolled Ag migration towards the surface.
- Vacuum Tribological Properties of W-S-N Coatings Synthesized by Direct Current Magnetron SputteringPublication . Yaqub, Talha Bin; Yaqoob, Khuram; Mukhtar, Amir; Fernandes, Filipe; Bondarev, Andrey; Ferreira, Fabio; Al-Rjoub, Abbas; Cavaleiro, AlbanoThis work deals with the investigation of the tribological performance of DC magnetron sputteredW-S-N coatings under vacuum atmosphere, as part of the exploration of multi-environment sliding properties of W-S-N solid lubricants. This study is part of the systematic testing of W-S-N solid lubricants in different environments, especially vacuum, which is often ignored. The trend is to test sliding properties in dry N2 by considering it as replacement of vacuum environment testing. This approach is not appropriate. In this work, a set of coatings was synthesized with N-alloying content in the range of 0–25.5 at.%. A maximum S/W ratio of 1.47 was observed for the pure WSx coating. A maximum hardness of 8.0 GPa was observed for 23 at.% of N-alloying. The coating with the lowest N content (14.6 at.%) displayed the lowest friction, specific wear rate and wear scar depth under vacuum conditions. Despite superior sliding performance at room temperature (35% humidity), 200 C and dry nitrogen conditions, the performance of the WSN12.5 coating deteriorated vacuum environment.