Microstructure Dependence of Effective Thermal Conductivity of EB-PVD TBCs.

Shi-Yi Qiu,Hong-Bo Guo,Yue Ma,Chen-Guang Huang,Chen-Wu Wu

doi:10.3390/ma14081838

Abstract

Microstructure dependence of effective thermal conductivity of the coating was investigated to optimize the thermal insulation of columnar structure electron beam physical vapor deposition (EB-PVD coating), considering constraints by mechanical stress. First, a three-dimensional finite element model of multiple columnar structure was established to involve thermal contact resistance across the interfaces between the adjacent columnar structures. Then, the mathematical formula of each structural parameter was derived to demonstrate the numerical outcome and predict the effective thermal conductivity. After that, the heat conduction characteristics of the columnar structured coating was analyzed to reveal the dependence of the effective thermal conductivity of the thermal barrier coatings (TBCs) on its microstructure characteristics, including the column diameter, the thickness of coating, the ratio of the height of fine column to coarse column and the inclination angle of columns. Finally, the influence of each microstructural parameter on the mechanical stress of the TBCs was studied by a mathematic model, and the optimization of the inclination angle was proposed, considering the thermal insulation and mechanical stress of the coating.

Highlights

Thermal barrier coatings (TBCs) are applied on the surface of superalloy substrates to reduce the working temperature of the superalloy substrate and avoid high temperature oxidation wear and corrosion [1,2,3]
Rätzer-Scheibe et al [24] studied the dependence of thermal conductivity on the thickness of Electron beam physical vapor deposition (EB-PVD) thermal barrier coatings, and the results indicated that thermal conductivity of the thermal barrier coating would increase with thickness of the coating increasing
The effect of microstructural parameters on the effective thermal conductivity of the EB-PVD thermal barrier coating was investigated considering the constraint by mechanical stress

Summary

Introduction

Thermal barrier coatings (TBCs) are applied on the surface of superalloy substrates to reduce the working temperature of the superalloy substrate and avoid high temperature oxidation wear and corrosion [1,2,3]. A classical thermal barrier coating structure is composed of a ceramic coat and bonding coat. The former is mainly for thermal insulation, while the latter is to relieve the stress caused by thermal expansion mismatch between the superalloy and ceramic coat [4,5,6,7]. Electron beam physical vapor deposition (EB-PVD), an advanced thermal barrier coating preparative technique, works by electron beam bombardment making the target material melt quickly, evaporate and deposit on the surface of the substrate to form the coating. Due to the lack of transverse discontinuous interface impeded heat flow in the column microstructure, the thermal insulation performance of the EB-PVD coating is not good enough [11,12,13,14]

Methods

Results

Conclusion