TGO对热障涂层失效的作用分析

Influence of Thermally Grown Oxide on Failure of Thermal Barrier Coating

热生长氧化物(TGO)的形成与长大是热障涂层失效的根本原因。先在IC10高温合金基体上超音速火焰喷涂(HVOF)NiCoCrAlTaY粘结层(BC层),再等离子喷涂二元稀土氧化物稳定氧化锆Sc2O3-Y2O3-ZrO2,喷涂样在1 100℃恒温氧化,利用扫描电镜(SEM)、能谱仪对断面形貌、成分进行分析,讨论了TGO的形成机理及其与热障涂层失效的关系。结果表明:随着恒温氧化时间增加,TGO层底部的Al含量下降,上部、中间弥散颗粒及底部的Ni含量均增加,上部、中间弥散颗粒中Cr含量均减少;喷涂样氧化140 h后,TGO层由靠近陶瓷层的富(Cr,Al)2O3层、弥散其间的富Ni颗粒和靠近BC层的Al2O3层组成;TGO的生长速度先由Al与O2化学反应速度决定,接着受BC层金属元素扩散速度影响,最后由化学反应速度和扩散速度共同控制;减少TGO中的有害氧化物含量以降低涂层内的应力,可有效提高涂层的使用寿命。

NiCoCrAlTaY bond coating was initially fabricated on IC10 high-temperature alloy substrate by high-velocity oxy-fuel spraying.Then Sc2O3-Y2O3-ZrO2 coating was prepared as a thermal barrier coating on the bond coating by plasma spraying.Finally,as-sprayed specimens were subjected to isothermal heat-treatment at 1 100 ℃.The cross-sectional morphology and composition of the oxidized coating specimens were analyzed by means of scanning electron microscopy and energy dispersive spectrometry.The formation process of thermally grown oxide(TGO) and its effect on the failure of the thermal barrier coating were investigated.It was found that Al content in the bottom layer of the TGO coating as well as Cr content in the top layer and intermediate dispersive particulates declined with extending oxidation time,while Ni content in the top and bottom as well as intermediate dispersive particulates of the TGO coating rose therewith.After the as-sprayed specimen was oxidized for 140 h,TGO coating composed of(Cr,Al)2O3-rich layer near to the ceramic coating,Ni-rich dispersive particulates,and Al2O3 layer near to the bond coating was formed.The growth rate of the TGO coating was dominated by the chemical reaction rate of Al and O2,the diffusion rate of metal elements in the bond coating,and the chemical reaction rate in association with the diffusion rate in turn.