Multiscale Pores in TBCs for Lower Thermal Conductivity
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Multiscale Pores in TBCs for Lower Thermal Conductivity Wei-Wei Zhang1,2,3 • Guang-Rong Li1 • Qiang Zhang1 • Guan-Jun Yang1
Submitted: 16 January 2017 / in revised form: 9 May 2017 Ó ASM International 2017
Abstract The morphology and pattern (including orientation and aspect ratio) of pores in thermal barrier coatings (TBCs) significantly affect their thermal insulation performance. In this work, finite element analysis was used to comprehensively understand the thermal insulation effect of pores and correlate the effective thermal conductivity with the structure. The results indicated that intersplat pores, and in particular their aspect ratio, dominantly affect the heat transfer in the top coat. The effective thermal conductivity decreased as a function of aspect ratio, since a larger aspect ratio often corresponds to a greater proportion of effective length of the pores. However, in conventional plasma-sprayed TBCs, intersplat pores often fail to maximize thermal insulation due to their distinct lower aspect ratios. Therefore, considering this effect of aspect ratio, a new structure design with multiscale pores is proposed and a corresponding structural model developed to correlate the thermal properties with this pore-rich structure. The predictions of the model are well consistent with experimental data. This study provides comprehensive understanding of the effect of pores on the thermal insulation performance, shedding light on the possibility of structural tailoring to obtain advanced TBCs with lower thermal conductivity.
& Guan-Jun Yang [email protected] 1
State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, China
2
Institute of Publication Science, Chang’an University, Xi’an 710064, China
3
School of Materials Science and Engineering, Chang’an University, Xi’an 710064, China
Keywords aspect ratio multiscale pores plasma spraying thermal barrier coatings thermal property
Introduction Thermal barrier coatings (TBCs) provide substantial benefits by protecting metal components in hot sections, driving development of modern propulsion and energygenerating gas turbines with enhanced efficiency and extended lifetime (Ref 1, 2). A typical TBC system often exhibits multilayer structure composed of an oxidationresistant metallic layer (bond coat) deposited on a superalloy component prior to an insulating ceramic layer (top coat) (Ref 3). The enhanced efficiency of TBCs is primarily attributed to the thermal insulation contributed by the top coat with low thermal conductivity. Consequently, a key issue for TBCs is to maximize the temperature drop across the top coat, with the aim of permitting higher turbine entry temperatures to meet the ever-increasing requirements for improved engine efficiency (Ref 4). The thermophysical properties (e.g., thermal conductivity) of the top coat are extremely important to control the temperature drop. Therefore, to achieve improved high-temperature and the
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