A Novel Plasma-Sprayed Nanostructured Coating with Agglomerated-Unsintered Feedstock
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ang Gao, Yan Zhao, Deming Yang, and Jianyi Gao (Submitted June 6, 2015; in revised form October 12, 2015) In this article, an unusual agglomerated powder of Y2O3-stabilized ZrO2 (YSZ) that did not undergo calcination was introduced as a feedstock for thermal spray deposition using internal injection atmospheric plasma spray (APS) and the very-low-pressure plasma spray (VLPPS) methods at an ambient pressure of 100-150 Pa. The results show that the microstructure of the coating is influenced not only by the spray parameters (such as arc gas composition, ambient pressure, and arc current) but also by the manufacture process of the agglomerates particularly the sintering process. The microstructure of the coating exhibited a bimodal structure if the APS method was used; in this case, the microstructure resembles that of other nanostructured coatings using regular agglomerated-sintered feedstock. A coating having a novel fully nano-equiaxed structure with a microporosity of 10-15% was first successfully deposited using VLPPS with 20Ar-30He SLPM plasma gas flows at a current of 500 A. The experimental results suggest that the nano-scale equiaxed structure in the coating is directly formed from original nanoparticles that had undergone melting, while inside the nozzle they were subsequently solidified on the substrate. The VLPPS method, which offers some unique advantages over the conventional plasma spray process, is generic in nature and can potentially be used to deposit a wide variety of ceramic coatings for diverse applications. The thermal conductivity values of the fully nanostructured and bimodal structured coatings were measured, and the microstructures of the coating both in the assprayed state and after heat treatment for 10 h at 1300 °C were investigated.
Keywords
agglomerates, nano-equiaxed structure, plasma spray, thermal barrier coating
1. Introduction Nanostructured yttria-stabilized zirconia (YSZ) coatings have been demonstrated to enhance the properties of durability and reduced thermal conductivity (Ref 1-4). As a result of these characteristics, the nanostructured YSZ coatings may have an application as advanced thermal barrier coatings (TBCs). It is well known that individual nanoparticles cannot be directly injected into the plasma plume to create a coating because they lack fluidness and the inertia required to cross the streamlines in the spray jet (Ref 5-7). To enable the thermal spraying of nanoparticles, a number of methods have been developed, including plasma spraying of nanostructured agglomerThis 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. Yang Gao, Yan Zhao, and Deming Yang, Thermal Spray Centre of the Dalian Maritime University, Dalian, China; and Jianyi Gao, School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 5706. Contact e-mail: [email protected].
Journal of Thermal Spray Tec
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