等离子喷涂La2Zr2O7热障涂层高温烧结的硬化行为

Sintering-stiffening Behavior of Plasma Sprayed LaZrO Thermal Barrier Coatings During High Temperature Exposure

热障涂层在高温服役过程中发生烧结和硬化,是引发涂层开裂和剥离失效的主要因素,因此掌握涂层烧结规律是进行涂层设计制备、寿命预测和工艺优化的前提。文中采用等离子喷涂技术制备La2Zr2O7热障涂层,在1250℃条件下进行涂层高温热暴露试验,表征了涂层高温烧结过程中力学性能的变化规律,从孔隙结构的角度揭示了涂层高温烧结硬化机理。研究结果表明,喷涂态La2Zr2O7涂层为典型的层状结构,硬度为(405±20)HV0.3,高温热暴露后涂层呈现先快后慢的硬化趋势,热暴露200 h后涂层硬度提高了80%。涂层结构分析表明,涂层物相保持不变,但涂层孔隙率呈现出先快后慢的下降规律。坐标轴变换处理后发现,硬度和孔隙率均呈现以10 h为临界的双阶段特性。通过对涂层孔隙结构的高温准原位观察,发现涂层孔隙初期多点桥接超快愈合、后期以边界推进方式缓慢烧结的双阶段烧结现象,从而揭示了La2Zr2O7热障涂层分阶段硬化的烧结机理,从而为发展抗烧结高性能热障涂层提供了新的理论依据。

The sintering of thermal barrier coatings leads to the stiffening during high temperature service,and thereby causes coating cracking and peeling failure.Therefore,understanding the coating sintering law is the premise of coating design,preparation,lifetime prediction and process optimization.La2Zr2O7 thermal barrier coatings were prepared by plasma spraying technology.The high temperature thermal exposure test of coating was carried out at 1250℃.Firstly,the mechanical properties of the coating during high temperature sintering were characterized.Subsequently,the high temperature sintering-stiffening mechanism of the coating was revealed from the perspective of pore structure.Results show that the as-sprayed La2Zr2O7 coating is a typical layered structure with a hardness of(405±20)HV0.3.The coating exhibits a first fast sintering and then slow hardening tendency after high temperature exposure,and the coating hardness after 200 h thermal exposure is increased by 80%.The analysis of the coating structure shows that the phase of the coating remaines unchanged,but the porosity of the coating shows a first fast decrease and then slow decline.After the coordinate axis transformation,it is found that both hardness and porosity exhibites a twostage characteristic with a critical duration of 10 h.The quasi-in-situ observation of the pore structure suggests that the initial healing of pores proceeds very fast in a form of multi-point contact,and that the subsequent healing slows down in a form of single-contact and growth.Therefore,this can be responsible for the two-stage sintering mechanism of the La2Zr2O7,which makes fundamental contribution for the development of high performance thermal barrier coatings.