The Influence of Temperature on Frictional Behavior of Plasma-Sprayed NiAl-Cr 2 O 3 Based Self-Adaptive Nanocomposite Co
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M. Ramazani, F. Ashrafizadeh, and R. Mozaffarinia (Submitted November 5, 2012; in revised form June 3, 2013)
Frictional behavior of nano and hybrid-structured NiAl-Cr2O3-Ag-CNT-WS2 adaptive self-lubricant coatings was evaluated at a range of temperatures, from room temperature to 700 °C. For this purpose, hybrid structured (HS) and nanostructured (NS) composite powders with the same nominal compositions were prepared by spray drying and heat treatment techniques. A series of HS and NS coating samples were deposited on steel substrate by an atmospheric plasma spraying process. The tribological behavior of both coatings was studied from room temperature to 700 °C at 100° intervals using a custom designed high temperature wear test machine. Scanning electron microscopy was employed for the evaluation of the composite coatings and worn surfaces. Experimental results indicated that the hybrid coating had inferior tribological properties when compared to the nanostructured coating, showing the attractive frictional behavior on the basis of low friction and high wear resistance; the NS coating possessed a more stable friction coefficient in the temperature range of 25-700 °C against alumina counterface. Microstructural examinations revealed more uniformity in NS plasma-sprayed coatings.
Keywords
friction, high temperature wear, nanocomposite coatings, plasma spray, self-lubricant
1. Introduction Wear and friction are among the main failure causes in most industrial systems, and there is a growing interest to reduce the energy and weight loss due to wear (Ref 1, 2). There is an increased interest for solid lubricants due to their high performance in reducing friction and wear of engineering components. Selflubricant composite materials and coatings containing solid lubricants have a wide variety of applications, particularly at high temperature, high load, or vacuum environments. In recent years, self-lubricant nanocomposite coatings have been developed for a number of different applications, especially in tribology sector. A complicating factor is that lubrication must not only be effective at the high operating temperatures but also at low temperatures during engine starting and warm-up in humid or dry atmosphere. In some other applications,
M. Ramazani and F. Ashrafizadeh, Esfahan University of Technology, Esfahan, Iran; and M. Ramazani and R. Mozaffarinia, Malek Ashtar University of Technology, Shahin Shahr, Iran. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
for example, bearings in the aerospace mechanisms, the lubricant must be typically functional in vacuum (dry environment) as well as in air (humid environment) and over a wide temperature spectrum. The extreme environmental conditions of these systems require new friction and wear-protective coatings with unique tribological performance. Traditional lubricants like oil, grease, and conventional solid lubricants like MoS2 and Teflon (PTFE) lack such capabilities. These coatings contain some solid lubricant components that he
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