Development of next generation high temperature materials for high performance gas turbine

• Main Author: Zhang, P.
• Other Authors: Choy, K. L.
• Published: University College London (University of London) 2016
• Subjects: 540
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.746069

Thermal barrier coatings (TBCs) are advanced protective coating systems used to protect metallic substrates at high-temperature application. Currently, the state-of-the-art industrial TBC material is 6-8wt% Y2O3 stabilized ZrO2 (6-8YSZ), but it cannot be used over 1200oC for a long time due to sintering behaviour and phase transformation. The purpose of this thesis was to explore new thermal barrier materials that can be used at high temperature for a long time to replace YSZ. Micron lanthanum titanium aluminum oxide (LaTi2Al9O19, LTA) has been proven as a very promising thermal barrier material due to low thermal conductivity, and excellent phase and thermochemical stability. The main drawback of LTA is the low fracture toughness. Therefore, this thesis studied nano-structured LTA, toughened LTA, and ion doped LTA synthesized by sol- gel method, and LTA and toughened LTA coatings on steel substrate prepared by air plasma spray (APS). The experimental results indicate that compared to micron LTA, the nano-structured LTA had higher coefficients of thermal expansion (CTEs) and comparable thermochemical stability. LTA toughened by 10vol% tetragonal zirconia (LTA-4YSZ) was synthesized by a hybrid sol-gel method. The ceramic composite LTA- 4YSZ had lower thermal conductivity of approximately 1.054 W/(m·K) at room temperature, stable CTEs, better sintering resistance, and mechanical properties. Single phase ion doped LTA by gadolinium was obtained with a Gd3+ content of less than 10mol%, La0.9Gd0.1Ti2Al9O19 (L9G1) had higher CTEs around 11.7×10-6 oC-1 at 950oC, lower thermal conductivity circa. 1.404 W/(m·K) at room temperature, and better sintering resistance than LTA. The APS produced LTA-4YSZ coatings were prepared with optimized granulated powders, which were typical APS coatings with five types of defects: cracks, gaps, cavities, voids, and interspace.