等离子喷涂La₂Zr₂O₇热障涂层高温烧结的硬化行为

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) HV_0.3. 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 two-stage 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.