温度梯度热循环下纳米7YSZ陶瓷层结构演变

目的采用低温超音速等离子喷涂(LT-HVOF)在镍基高温合金基体(K417)上制备了NiCoCrAlYTa粘结层,使用大气等离子喷涂(APS)在粘结层上制备了纳米7%Y_2O_3-ZrO_2(7YSZ)陶瓷涂层,以获得温度梯度热循环下纳米陶瓷层的结构演变机制。方法通过燃气热冲击实验仪对热障涂层模拟真实服役条件下温度梯度热循环的工作环境,采用一维稳态热传导模型计算了热障涂层中各涂层界面的温度,探讨了在热驱动作用下等径晶粒和非等径晶粒的扩散长大机制。结果热循环次数为40次时,涂层近表面出现了烧结致密化现象,而陶瓷层底部涂层保持原来的结构。热循环次数增加到460次时,整个陶瓷层断面都发生了烧结致密化现象。结论温度是涂层烧结致密化的主导因素。涂层中当等大晶粒接触形成弯曲颈时,由于弯曲颈只受水平方向静压力作用,晶粒中原子扩散速率慢,导致晶粒长大速率较慢;而当非等大晶粒接触形成弯曲颈时,在晶粒接触弯曲颈处存在一偏大晶粒方向的剪切力,其导致晶粒向弯曲颈扩散速率增加,晶粒长大速率较快。

Structure Evolution of Nano-7YSZ Ceramic Coating During Gradient Thermal Cycle

The work aims to get the structure evolution mechanism of nano ceramic coating during gradient thermal cycle by preparing NiCoCrAlYTa bonding layer on nickel-based superalloy (k417) by low temperature-high velocity oxygen flame (HVOF) and nano-7YSZ ceramic coating on the bonding layer by air plasma spraying. Gradient thermal cycle test was carried out on nano-7YSZ TBC with a flame tester to simulate service condition of thermal barrier coating (TBC) in turbine engine. In-terface temperatures in TBC were calculated based on one-dimensional model of steady heat conduction. Provided with 40 thermal cycles, the coating subsurface was subject to sintering densification, while base coating of the ceramic layer reserved the original structure. As the thermal cycle number increased to 460 times, entire section of the ceramic layer was subject to sinter-ing densification. The coating sintering densification is mainly affected by temperature. When isometrical grains in the coating contact and form crooked neck, the grains grow slowly since the neck bears static stress in horizontal direction only and diffu-sion rate of atoms in the grains is slow. However, when non-isometrical grains in the coating contact and form crooked neck, the grains grow quickly since shear force in direction of large grain is present on the neck and the diffusion rate of grains is accele-rated.