Size effect on heat transfer and ions distribution in yttria-stabilized zirconia
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摘要: 8mol%Y2O3稳定ZrO2(8mol%Yttria-stabilized zirconia，8YSZ)作为热障涂层被广泛应用于燃气轮机和航空发动机，以减少热气体和金属部件之间的传热。但随着服役温度的提升，对其热性能的研究很难进行。采用非平衡分子动力学模拟的方法研究了模型尺寸效应对8YSZ热导率和离子扩散的影响，探讨了服役条件下YSZ的离子扩散及热输运行为。以立方8YSZ(c-8YSZ)作为研究对象，模拟服役温度为1273~1473 K时，分别计算了模型横截面积为4a×4a、5a×5a、6a×6a (a为晶格常数)的热导率，发现横截面积对计算结果影响较小。选取横截面积为5a×5a时，对比了5a、15a、25a、35a、45a、50a、55a、60a、65a不同结构长度模型的热导率计算结果，进行尺寸效应研究，确定5a×5a×60a为模型最佳尺寸。同时揭示了1273~1473 K下c-8YSZ热输运机制，发现c-8YSZ与四方8YSZ(t-8YSZ)存在不同的声子散射，发现增强声子散射能够有效抑制YSZ服役状态下的热输运能力，为提高热障涂层在高温服役状态下的隔热性能提供了理论依据。Abstract: 8mol%Y2O3-stabilized ZrO2 (8mol% Yttria-stabilized zirconia, 8YSZ) is widely used as thermal barrier coatings (TBCs) to reduce heat transfer between hot gases and metallic components in gas-turbine engines. However, with the increase of service temperature, it’s difficult to study the thermal performance of 8YSZ. The influence of the model size effects on thermal conductivity and ion diffusion of 8YSZ were investigated through non-equilibrium molecular dynamics simulations (NEMD). Besides, the ion diffusion and thermal transport behavior of YSZ were explored under service conditions. Using cubic 8YSZ(c-8YSZ) as the study object, the thermal conductivity was calculated for model cross-sectional areas of 4a×4a, 5a×5a and 6a×6a (Lattice constant a) at simulated service temperatures of 1273-1473 K. It was found that the cross-sectional area had a small effect on the calculated results. When the cross-sectional area of 5a×5a was selected, the thermal conductivity calculations of the models with different structure lengths of 5a, 15a, 25a, 35a, 45a, 50a, 55a, 60a and 65a were compared, and the size effect was studied to determine 5a×5a×60a as the best size of the model. The thermal transport mechanism of c-8YSZ at 1273-1473 K was also revealed, and the different phonon scattering between c-8YSZ and tetragonal 8YSZ(t-8YSZ) was also found. It was found that enhanced phonon scattering can effectively suppress the thermal transport capacity of YSZ in service, which provides a theoretical basis for improving the thermal insulation performance of thermal barrier coatings in high temperature service.
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图 1 8mol%Y2O3稳定ZrO2(8 YSZ)模型系统热浴示意图
Figure 1. Model system heat bath diagram on 8mol%Y2O3-stabilized ZrO2 (8 YSZ)
Lx—Model length; z—Direction of heat flux
图 2 8YSZ热导率随模型结构长度的变化关系(a为晶格常数)
Figure 2. Effect of model structure length on calculated thermal conductivity of 8YSZ (a is the lattice constant)
Δ—Relative error between calculated and standard values of thermal conductivity
图 3 8YSZ在1473 K下不同模型中O2−的均方位移(MSD)
Figure 3. Mean square displacement (MSD) of O2− ions in different models at 1473 K for 8YSZ
图 4 8YSZ在1473 K下不同温度中O2−的MSD
Figure 4. MSD of O2− ions in different temperatures at 1473 K for 8YSZ
图 6 高温下立方8YSZ(c-8YSZ)模拟的热导率、实验和文献中四方YSZ (t-YSZ)模拟的热导率
Figure 6. Thermal conductivity of cubic 8YSZ (c-8YSZ) simulations at high temperatures, experimental and tetragonal YSZ (t-YSZ) simulations in the literature
表 1 分子动力学中所采用的势函数参数
Table 1. Potential functions used in molecular dynamics
Interatomic interactions/i-j Aij/eV ρij/nm Cij/(eV·nm6) Zr4+-O2− 985.869 0.0376 0 Y3+-O2− 1325.60 0.0349 0 O2−-O2− 22764.3 0.0149 2.789×10−5 Notes: Aij, ρij and Cij—Buckingham potential parameters. 
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