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Open Access Research Article Issue
Insight into the high-temperature tribological mechanism of VAlTiCrW high entropy alloy film: AlV3O9 from tribochemistry
Friction 2023, 11 (7): 1165-1176
Published: 08 September 2022
Downloads:39

High-entropy alloys have made significant progress in high mechanical properties, wear resistance, and corrosion resistance properties. Excellent tribological properties, especially high-temperature lubrication, have become another sought performance. In this work, VAlTiCrW high-entropy alloy film with body-centered cubic (BCC) structure was prepared on superalloy substrate by magnetron sputtering. It is found that the VAlTiCrW film shows very low friction coefficient of 0.15 and a low wear rate of 10-5 orders of magnitude at 800 °C. After 800 °C oxidation, the film can still obtain a friction coefficient of no more than 0.2 at 700 °C. XRD and TEM revealed the formation of ternary oxide AlV3O9 with preferred orientation of (002) crystal plane with large spacing of 0.71 nm on the wear surface of the film, a high-temperature lubricating phase that has not been reported, realizes the low friction coefficient. This AlV3O9 can be formed by tribochemical reaction under the thermal-mechanical action at 700 °C, but pre-oxidation at 800 °C is the prerequisite in order to form the precursors of V-rich and Al-rich oxide layer.

Research Article Issue
Anomalous enhancement oxidation of few-layer MoS2 and MoS2/h-BN heterostructure
Nano Research 2022, 15 (8): 7081-7090
Published: 23 May 2022
Downloads:55

Because of profound applications of two-dimensional molybdenum disulfide (MoS2) and its heterostructures in electronics, its thermal stability has been spurred substantial interest. We employ a precision muffle furnace at a series of increasing temperatures up to 340 °C to study the oxidation behavior of continuous MoS2 films by either directly growing mono- and few-layer MoS2 on SiO2/Si substrate, or by mechanically transferring monolayer MoS2 or hexagonal boron nitride (h-BN) onto monolayer MoS2 substrate. Results show that monolayer MoS2 can withstand high temperature at 340 °C with less oxidation while the few-layer MoS2 films are completely oxidized just at 280 °C, resulting from the growth-induced tensile strain in few-layer MoS2. When the tensile strain of films is released by transfer method, the stacked few-layer MoS2 films exhibit superior thermal stability and typical layer-by-layer oxidation behavior at similarly high temperature. Counterintuitively, for the MoS2/h-BN heterostructure, the h-BN film itself stacked on top is not damaged and forms many bubbles at 340 °C, whereas the underlying monolayer MoS2 film is oxidized completely. By comprehensively using various experimental characterization and molecular dynamics calculations, such anomalous oxidation behavior of MoS2/h-BN heterostructure is mainly due to the increased tensile strain in MoS2 film at elevated temperature.

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