Influence of FeCrAl Content on Microstructure and Bonding Strength of Plasma-Sprayed FeCrAl/Al 2 O 3 Coatings
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iang Zhou, Fa Luo, Wancheng Zhou, and Dongmei Zhu (Submitted July 7, 2015; in revised form November 16, 2015) Low-power plasma-sprayed FeCrAl/Al2O3 composite coatings with 1.5 mm thickness have been fabricated for radar absorption applications. The effects of FeCrAl content on the coating properties were studied. The FeCrAl presents in the form of a few thin lamellae and numerous particles, demonstrating relatively even distribution in all the coatings. Results show that the micro-hardness and porosity decrease with the increase in FeCrAl content. With FeCrAl content increasing from 28 to 47 wt.%, the bonding strength of the coatings with 1.5 mm thickness increases from 10.5 to 27 MPa, and the failure modes are composed of cohesive and adhesive failure, which are ascribed to the coating microstructure and the residual stress, respectively.
Keywords
bonding strength, cermet coatings, micro-hardness, plasma spraying
1. Introduction Radar absorption coatings have been widely investigated for the application as the components of high-speed aircraft, which need withstanding high temperature for a long time (Ref 1, 2). Composite materials formed by insulating ceramic matrix and conductive metallic particles, also known as cermets, have potential application for radar absorption coatings due to the singular combination of electrical, magnetic and mechanical properties. Moreover, cermet coatings can be prepared through many methods such as pulsed laser deposition (Ref 3), magnetron sputtering (Ref 4), electro deposition (Ref 5) and thermal spraying (Ref 6) etc. Among them, plasma spraying is a preferable viable technique, with such advantages of high achievable deposition efficiency, cost-effectiveness and very specific coating properties (Ref 7, 8). Recently, plasma-sprayed Al2O3-based cermet coatings attract more attention in radar absorption application because of the excellent mechanical properties of alumina such as low density, high strength and hardness (Ref 9). These coatings cover a wide range of materials including Nb/Al2O3 (Ref 10), Cr/Al2O3 (Ref 11) and Ni/Al2O3 (Ref Liang Zhou, School of Materials Science and Engineering, ChangÕan University, XiÕan 710064, China and State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xian 710072, China; and Fa Luo, Wancheng Zhou, and Dongmei Zhu, State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, XiÕan 710072, China. Contact e-mails: [email protected] and [email protected].
Journal of Thermal Spray Technology
12). In the Al2O3-based radar absorption coatings, metallic particles act as radar absorber, and alumina acts as filler. The radar absorption properties have been improved successfully in the aspect of electrical and magnetic parameters by changing the absorber content and coating thickness (Ref 10). Also, some alloy absorbers, such as NiCrAlY and FeCrAl, form dense and continuous protective alumina layer on the surface when they are exposed to high temperature. The alumina layer provides
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