Residual stress mapping in high yttria thermally sprayed zirconium oxide coatings

Need for high thermal efficiency in aero and land-based turbine engines push the envelope for low conductivity and high strength thermal barrier coatings (TBC’s). Prominent approach towards achieving this is through high yttria content in zirconia to stabilize zirconia . High yttria content degrades the thermal shock resistance of the TBC system. The project therefore aims to explore the residual stress profile of 8YSZ (as sprayed) and 20YSZ (in as sprayed and thermal shock conditions). Mapping residual stresses will provide qualitative information on the thermal shock life of the TBC system thereby eliminating the need of expensive and time-consuming thermal shock studies on all the possible chemistries. Due to the heavy lattice distortion unleashed by the high atomic number rare earth elements, it is expected that neutron diffraction would be able to predict the residual stress and quantify the thermal shock. Neutron diffraction residual strain analysis is expected to expedite the selection of the best composition that would suit both the requirements of thermal shock resistance as well as low thermal conductivity. Reduced tensile residual stress are known to be beneficial to the fatigue life of coatings leading to enhanced thermal cycling behavior – which demonstrates wider impact of this investigation.

航空航天与陆基涡轮发动机对高热效率的需求，推动了低导热率、高强度热障涂层（Thermal Barrier Coatings，TBCs）的性能极限突破。实现该目标的主流途径是在氧化锆中引入高氧化钇含量以稳定其晶型结构，但高氧化钇含量会劣化热障涂层系统的抗热震性能。因此本项目旨在探究8YSZ（喷涂态）以及20YSZ（喷涂态与热震工况下）的残余应力分布特征。通过绘制残余应力图谱，可获取热障涂层系统热震寿命的定性参考信息，从而无需针对所有候选成分开展昂贵且耗时的热震试验。由于高原子序数稀土元素会引发显著晶格畸变，中子衍射技术有望实现残余应力的预测与热震程度的量化表征。中子衍射残余应变分析技术，有望加速筛选同时满足抗热震性与低导热率要求的最优涂层成分。已知降低拉伸残余应力可提升涂层疲劳寿命，改善其热循环性能——这也体现了本研究的更广泛应用价值。