Microstructure and Properties of Porous Abradable Alumina Coatings Flame-Sprayed with Semi-molten Particles
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JTTEE5 25:264–272 DOI: 10.1007/s11666-015-0287-2 1059-9630/$19.00 ASM International
Microstructure and Properties of Porous Abradable Alumina Coatings Flame-Sprayed with Semi-molten Particles Chang-Jiu Li, Jiao Zou, Hui-Bin Huo, Jian-Tao Yao, and Guan-Jun Yang (Submitted May 23, 2015; in revised form July 17, 2015) High-efficiency gas turbines require high-temperature sealing by use of abradable porous ceramic coatings to increase engine efficiency. In this study, porous Al2O3 coatings were deposited by flame spraying; the coatings were applied in a semi-molten state by controlled melting of the sprayed powder particles. The effects of the degree of melting of the sprayed particles, which depends on spraying conditions, on coating microstructure and porosity were investigated. The degree of melting of the sprayed particles was characterized by use of 3D confocal laser microscopy. The porosity of the coating was estimated by image analysis. The results showed that the degree of melting of alumina particles can be changed from 70 to 30%, and thus coating porosity can be increased from 30% up to over 70%. The standard hardness test yielded no useful data for porous coatings deposited by use of sprayed particles with a degree of melting 60%. Pin-on-disk abrasion tests, performed at room temperature by use of an Inconel 738 (IN738) nickel-based superalloy pin with a spherical tip 5 mm in diameter, were conducted on the porous alumina coating to evaluate its abrasion behavior. It was found that for coatings of hardness 40% the wear weight loss of the IN738 pin was negligible despite the high rate of wear of the coating. It is evident that flame-sprayed porous alumina coatings of high porosity prepared by this approach have potential for use as abradable coatings for gas turbines operating at high temperatures.
Keywords
abradable, Al2O3, ceramic coating, degree of melting, flame spraying
1. Introduction Thermal spray coatings have been widely applied in different fields of industry to provide different mechanical parts with wear-resistance, corrosion-resistance, oxidation-resistance, and high temperature resistance. Among these applications, industrial gas turbines (IGT) and aerospace applications account for approximately 60% of the worldwide thermal spray market (Ref 1, 2). Different types of coating have been developed to enhance the performance and reliability of gas turbines; the coatings are applied to different components in a gas turbine, for example the inlet, compressor, combustor, and hot gas turbine sectors (Ref 2). In essence, two types of thermal This article is an invited paper selected from presentations at the 2015 International Thermal Spray Conference, held May 11–14, 2015, in Long Beach, California, USA, and has been expanded from the original presentation. Chang-Jiu Li, Jiao Zou, Hui-Bin Huo, Jian-Tao Yao, and GuanJun Yang, State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, XiÕan Jiaotong University, XiÕan, Shaanxi Province 710049, PeopleÕs Re
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