基于第一性原理计算研究YSZ相变影响热障涂层寿命机理

The mechanism of the YSZ phase transition affecting the durability of thermal barrier coatings via first-principles

关键词:  热障涂层  相变  第一性原理  热力学性能  寿命

Key words:  thermal barrier coatings  phase transformation  first principles  thermodynamic properties  durability.

摘要:

为分析陶瓷层(YSZ)相变过程中影响热障涂层寿命的深层次机理,采用第一性原理计算方法分析了单斜相(M相)、四方相(T相)、立方相(C相)3种不同相结构ZrO₂单胞的电子结构与力学性能,并在单胞基础上构建了不同质量分数Y₂O₃掺杂ZrO₂超晶胞模型,表征了YSZ相组成与微观结构对其热力学性能的影响。结果表明:Y₂O₃掺杂提升了ZrO₂的结构稳定性。与T相相比,YSZ的M相生成焓更负,结构稳定性更高。T相到M相转变时产生晶格结构和氧空位浓度的变化,导致YSZ隔热性能下降,在引起粘结层表面氧化速度增加的同时,还诱发温度升高,促进YSZ烧结。M相的泊松比高,YSZ由T相转变为M相时韧性增加。但是,T相转变为M相时,M相的高弹性模量导致涂层应力升高。因此,研究YSZ高温相变对涂层寿命的影响时,应从隔热能力和力学性能等多个方面开展。

Abstract:

To analyze the deep-seated mechanism of ceramic topcoat (YSZ) phase transformation affecting the durability of thermal barrier coatings,the electronic structure and mechanical properties of zirconia cells with monoclinic, tetragonal and cubic phases were analyzed by first-principles calculation. A model of Y₂O₃-doped ZrO₂ supercell was established, and the effects of YSZ phase composition and microstructure on its thermodynamic properties were investigated. The results show that Y₂O₃ doping enhances the structural stability of ZrO₂. Compared with the T-phase, the generation enthalpy of M-phase is more negative, and the structural stability is higher. The T-to M-phase transformation comes with the change of the lattice structure and oxygen vacancy concentration, decreasing the thermal insulation performance of YSZ.Both temperature of the bond coat and YSZ coating increase, elevating the oxidation rate of bond coat and sintering rate of YSZ.YSZ toughness increases with phase transformation because of a higher Poissons ratio of M-phase. However, the T-phase has a lower elasticity modulus, decreasing the thermal stress in TBCs. Therefore, when studying the effect of YSZ high-temperature phase transformation on the durability of coatings , it is essential to consider aspects such as thermal insulation capability and mechanical properties.