A New Type of Self-lubricated Thermal Spray Coatings: Liquid Lubricants Embedded in a Metal Matrix N. Espallargas and S. Armada (Submitted June 8, 2014; in revised form August 19, 2014) Oils and greases are commonly used for lubricating, rotating and sliding systems such as bearings, gears, connectors, etc. The maintenance of such lubricated systems in some applications where access is difficult (e.g., offshore wind farms and subsea equipment) increases the operational costs. In some cases, it can be thought that the use of solid lubricants (MoS 2 , PTFE, graphite, etc.) embedded in coatings could be a solution for such applications; however, the mechanical and dynamic conditions of most of the systems are not appropriate for solid lubricants. Despite this, solid lubricants such as PTFE and MoS 2 have been largely employed in different industries, especially in those applications where liquid lubricants cannot be used and when the dynamic conditions allow for it. Self-lubricated coatings have been a major topic of interest in thermal spray in the last decades. Although the use of liquid lubricants is desirable whenever it is possible, limited research has been addressed toward the development of self-lubricated coatings containing liquid lubricants. One of the main reasons for this is due to the complexity of embedding liquid lubricant reservoirs inside the coating matrix. In the present work, a new type of liquid-solid self- lubricated coatings is presented, being the matrix a metal alloy. Three thermal spray techniques used were as follows: arc-spray, plasma spray, and HVOAF. The metal matrices were two stainless steel types and liquid lubricant-filled capsules with different liquid contents were used. No degradation of the capsules during spraying was observed and the coatings containing capsules were able to keep a low coefficient of friction. The optimal performance is found for the coatings obtained at the lowest spraying temperature and velocity. Keywords friction reduction, liquid-solid coatings, lubricant release, metal matrix, self-healing, self-lubricated coatings 1. Introduction The reliability of large industrial sectors is dependent on the performance of critical rotating components such as bearings, seals, shafts, and barrels. Those may suffer from scuffing/galling of the material if lubrication is not prop- erly maintained. Lubricants reduce friction and protect against wear as long as a lubricant film separates the moving parts involved in the process. Wear-resistant coatings are used in demanding conditions for protecting surfaces against wear or for tailoring the coefficient of friction (COF) of moving parts. Their use includes critical components such as airplanes landing gears, pistons and cylinders for engines, valves, bearings, etc. In almost all these applications, lubricants are used and required to minimize wear and friction between the moving parts. However, lubricant leakages or lubricant supply failures during operation can lead to lubricant starving conditions, eventually resulting in failure and downtimes and both energy and economical losses. Failures and downtimes in industrial applications require maintenance periods that can vary in length depending on the component. Self- lubricating wear-resistant coatings are proposed in this context and expected to reduce maintenance frequency and machinery failures in moving parts (Ref 1, 2). Thermal-sprayed coatings that incorporate multiple phases (ceramic-metal, metal-polymer, etc.) have been the subject of intensive investigation and industrial use, as they provide enhanced mechanical and tribological performance. One specific goal has been to combine the properties of hard, wear-resistant phases with those of lubricious solid phases (Ref 3-5). However, the current state of the art of thermal spray self-lubricated coatings is restricted to solid lubricants. Solid lubricants obtained as coatings have been used in applications, where liquids are forbidden (i.e., in vacuum or space applications), but their high price and properties pre- vent them to be a competitive alternative to liquid lubricants. Thus, a new family of self-lubricating coatings as the one proposed in this paper aims at avoiding unlubricated contacts This article is an invited paper selected from presentations at the 2014 International Thermal Spray Conference, held May 21-23, 2014, in Barcelona, Spain, and has been expanded from the original presentation. N. Espallargas, Tribology Lab, Faculty of Engineering Science and Technology, Department of Engineering Design and Materials, Norwegian University of Science and Technology, NTNU, 7491 Trondheim, Norway; and S. Armada, Tribology Lab, SINTEF, Materials and Chemistry, 7465 Trondheim, Norway. Contact e-mail: nuria.espallargas@ntnu.no. JTTEE5 24:222–234 DOI: 10.1007/s11666-014-0152-8 1059-9630/$19.00 Ó ASM International 222—Volume 24(1-2) January 2015 Journal of Thermal Spray Technology Peer Reviewed