长寿命热障涂层的剥落机理及抗剥落结构设计

涂覆于高温合金热端部件表面的热障涂层,具有隔热防护作用,属新一代燃气轮机的关键核心技术。等离子喷涂制备的热障涂层隔热性能好,但长时间高温服役后存在开裂剥落问题,引发基体烧蚀、造成巨大经济损失。因此,发展长寿命热障涂层是该技术领域的重大难题。本文从等离子喷涂热障涂层的独特层状结构特征入手,阐述涂层在高温服役中结构和性能的演变规律,揭示涂层剥落失效机理,总结长寿命热障涂层设计方法。研究表明,等离子喷涂热障涂层呈现以连通2D孔隙为主的层状多孔结构,具有优异的隔热功能和协调应变能力。然而,涂层在高温服役中发生烧结,2D孔隙大量消失,涂层显著刚化,使热障涂层开裂驱动力急剧增加,引发微观裂纹扩展并贯通形成大尺度裂纹,导致涂层最终剥落失效。据此,分别从降低开裂驱动力和增加开裂阻力两方面着手,总结抗开裂新结构涂层设计方法,为研发长寿命热障涂层指明了发展方向。在未来研究中,如何保证涂层高隔热和长寿命并同时兼顾经济性,是发展新一代高性能热障涂层的重点方向。

Failure mechanism and cracking-resistant design of thermal barrier coatings with long life span

Thermal barrier coatings (TBCs) are deposited on metallic components to prevent heat flux due to their excellent thermal insulation function. Nowadays, TBCs have become the key core technology of the new generation gas turbines. TBCs prepared by plasma spraying method are more readily to be failed, which negatively affect the thermal insulation and may cause substrate erosion. Therefore, long life span is an important guarantee for TBCs to achieve thermal barrier function. This paper described the failure mechanism of plasma sprayed TBCs and crack-resistant designs. To begin with, the essential characteristics of plasma sprayed TBCs were revealed. Plasma sprayed TBCs appeared to be lamellar structure with connected 2D pores. As a result, the plasma sprayed TBCs have excellent thermal insulation and strain tolerance at as-deposited state. By thermal exposure, the density of 2D pores is decreased significantly, which dominantly account for the degradation of strain tolerance and thermal insulation. Subsequently, the failure mechanism of plasma sprayed TBCs is revealed. The degradation of strain tolerance leads to increase of driving force for cracking. Consequently, the micro-scale cracks are extended and connected to form large-scale cracks, which is responsible for the failure of plasma sprayed TBCs. Finally, cracking-resistant designs are reviewed from two aspects: decreasing driving force and increasing fracture toughness. It is worth noting that the current cracking-resistant design often has poor performance on thermal insulation. In future research, how to ensure high thermal insulation and long life of the coating while considering the economy is the key direction of the development of a new generation of high-performance thermal barrier coatings.