Search

BACKGROUND AND OBJECTIVES: In urban conditions, traffic flows are equipped with various types of braking devices operating in an aperiodic cyclic braking mode with a high surface-volume temperature of their friction pairs. Theoretical and experimental studies of hydrogen wear of movable and stationary joints at variable electrical surface-volume temperatures and equivalent stresses caused by pulsed specific loads, contributing to the emergence of gradients, made it possible to establish the following: positive and negative values of the heat of transfer correspond to forces directed, towards more cold or warmer parts of the product. Hydrogen moves in the metal friction element to its more heated section. Due to the mutual mass transfer of materials of friction pairs, the sign of their polarity changes, and negatively charged external hydrogen enhances the negative electronic field of the metal friction element, and as a result, leads to intensive wear of pairs of friction elements of the brakes. The purpose of the article is to assess the electron-ion interaction during hydrogen wear on the working surfaces of metal friction elements of friction pairs of brake devices. METHODS: The data was obtained on a model disc, drum, and band-shoe brake and processed using a computer program package. As a result, graphical dependences of the main parameters of the brakes on the duration of hydrogenation were obtained. FINDINGS: The research results have shown that the described main stages of hydrogen wear and destruction of a metal friction element during electrothermal-mechanical friction, as well as the influence of dislocation and double electrical layers in brake friction pairs, will be able to justify the choice of ways and methods to suppress hydrogenation and prevent the destruction of surfaces and, as a result, reduce hydrogen wear by 15% and improve the performance parameters of brake pairs by 10%. CONCLUSION: This study examined the factors affecting the wear of metal brake friction elements of urban infrastructure vehicles. Empirical results have shown that positive and negative heat transfer values correspond to forces directed, towards colder or warmer parts of the product. These results can provide important information to factory designers for more efficient development of friction pairs of friction units, and researchers for further research and improvement of brake performance. [ABSTRACT FROM AUTHOR]

We simulate the conjugation of crystal lattices of two-dimensional Mg2Si layers with atomically clean Si(001)2×1 and Si(110)"16×2" surfaces. Thick films are grown by molecular-beam epitaxy (MBE) through the formation of Ca2Si seed layers. For a Si(001) substrate, three different silicides are formed in a 140-nm thick film at a temperature of T = 300°C at a Ca-to-Si deposition rate ratio of 4.7: Ca2Si, CaSi, and hR3-CaSi2 with comparable contributions. With a decrease in the MBE-growth temperature to 250°C and a Ca-to-Si deposition-rate ratio of 8.4, a polycrystalline Ca2Si film is formed on Si(110) with the minimal contribution from CaSi. Polycrystalline and epitaxial Ca2Si films with thicknesses from 22 to 114 nm are grown on Si(111) substrates by the sacrificial-template method and MBE growth at a temperature of 250°C and different ratios of Ca and Si deposition rates (4.0–20.0). The minimum deposition-rate ratio ensures single-phase growth with the Ca2Si(100)/Si(111) epitaxial ratio; as it increases from 7.3, polycrystalline films grow with three orientations on Si(111): Ca2Si(100), Ca2Si(110), and Ca2Si(111). In Ca2Si films, regardless of their structure, the fundamental transition is masked by the Urbach edge in the photon-energy range of 0.78–1.0 eV, and then the second direct interband transition is identified (E2d = 1.095 ± 0.1 eV). [ABSTRACT FROM AUTHOR]