Stiffening-resistant composite TBCs counteracting the substrate constraint effect during thermal exposure

Abstract

Thermal barrier coatings (TBCs) endow metal components with an increased capacity to endure exposure to high temperatures. Plasma-sprayed TBCs exhibit excellent thermal insulation performance and are widely used in land-based thermal protection systems. However, plasma-sprayed TBCs are more prone to cracking during usage, significantly limiting their applications. The main issue is the sintering-induced stiffening that enhances the cracking driving force. In this work, stiffening-resistant TBCs were fabricated using a composite structure that counteracts the substrate constraint effect. First, the substrate constraint effect on the TBCs was studied based on the surface roughness. The results revealed that stiffening was the primary cause of substrate constraint-related failure. Two-dimensional (2D) interface gaps were spontaneously formed during thermal exposure, which could reduce stiffening by 20%. Moreover, the healing behavior of the 2D gaps was analyzed and used to explain the stiffening-resistant behavior. Finally, the effect of the newly formed 2D gaps on the lifespan of the TBCs was analyzed. Detailed simulations suggested that the newly formed 2D gaps were capable of reducing the strain energy release rate and led to the growth of large in-plane cracks. For future applications, it is necessary to fully take advantage of the newly-formed 2D gaps by avoiding their negative effects on TBC life span.