Current Issue : April - June Volume : 2012 Issue Number : 2 Articles : 4 Articles
The surface degradation of metals in boiler tubes and turbines in high-temperature corrosive environments causes severe problems\r\nin fuel combustion power plant systems.High-temperature resistant materials have been recently developed using a thermal barrier\r\ncoating (TBC) and high-chromium alloys. Oxide films or coatings formed on metal surfaces at high temperatures can sometimes\r\ndecrease the corrosion rate. However, the damage to the material is often accelerated by the mechanical removal of corrosion\r\nproducts from the material surface. It is therefore very important to investigate the mechanical and adhesive properties of the\r\noxide films or coatings on metal surfaces used in high-temperature environments. This paper introduces a tribological method\r\nthat uses a single spherical projectile impact at high temperature to measure the mechanical and adhesive properties of oxide\r\nfilms formed on various metal surfaces. Impact tests were performed on the surfaces of oxide films after their growth in a hightemperature\r\nfurnace, and the deformed or fractured surfaces were observed in order to measure the mechanical and adhesive\r\nproperties. The mechanical and adhesive properties of an elastic modulus, fracture, and exfoliation stresses were measured using\r\nthe impact method, and the results depended on the type of metal oxide films and on the high-temperature environment....
The hysteretic part of the friction coefficient for rubber sliding on an ideal rigid, rough surface has been investigated by FE\ntechnique. The FE models were created by using two different FE softwares, ABAQUS and MSC.MARC. The surface roughness\nhas been considered by using two different sine waves having a wavelength of 100 �µm and 11.11 �µm, as well as their superposition.\nParameters of the viscoelastic material models of the rubber were gained, firstly from a fit to the measured storage modulus,\nsecondly from a fit to the measured loss factor master curve of the rubber. The effect of viscoelastic material models, comparing\n10-term and 40-term generalized Maxwell models was also considered together with the temperature effect between -50 and\n150?C. According to the results, both postprocessing methods, namely, the reaction force and the energy-based approach, show\nvery similar coefficients of friction. The 40-term Maxwell model fitted to both the storage modulus and loss factor curve provided\nthe most realistic results. The tendency of the FE results has been explained by semianalytical theory....
Current research on room-temperature ionic liquids as lubricants is described.\r\nIonic liquids possess excellent properties such as non-volatility, non-flammability, and\r\nthermo-oxidative stability. The potential use of ionic liquids as lubricants was first\r\nproposed in 2001 and approximately 70 articles pertaining to fundamental research on\r\nionic liquids have been published through May 2009. A large majority of the cations\r\nexamined in this area are derived from 1,3-dialkylimidazolium, with a higher alkyl group\r\non the imidazolium cation being beneficial for good lubrication, while it reduces the\r\nthermo-oxidative stability. Hydrophobic anions provide both good lubricity and significant\r\nthermo-oxidative stability. The anions decompose through a tribochemical reaction to\r\ngenerate metal fluoride on the rubbed surface. Additive technology to improve lubricity is\r\nalso explained. An introduction to tribology as an interdisciplinary field of lubrication is\r\nalso provided....
The lubrication mechanism of aluminium alloy slid against steel was investigated from the standpoint of surface chemistry. Low\r\nfriction and low wear were observed using glycerol mono-olate in a hydrocarbon as lubricant. Increase in the silicon content\r\nin the aluminium alloy during rubbing was observed by surface analyses using (1) Auger electron spectroscopy, (2) scanning\r\nelectron microscopy along with energy dispersive X-ray spectroscopy, and (3) X-ray photoelectron spectroscopy. Mild removal of\r\nthe passive state (aluminium oxide) from the uppermost surface by the additive during the running-in process was proposed as\r\nthe lubrication mechanism. The importance of additive chemistry that improves the running-in process was pointed out....
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