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

Abstract

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.

Keywords

• thermal barrier coatings
• plasma spraying
• failure mechanism
• cracking-resistant design
• long life span