Strain/sintering co-induced multiscale structural changes in plasma-sprayed thermal barrier coatings

Abstract

During thermal exposure, performance degradation is a main headache for thermal barrier coatings. However, most study to understand the performance evolution is often based on single effect of sintering with free-standing samples. Actually, the TBCs would be co-affected by sintering and strain caused by mismatch of thermal expansion coefficient (CTE). In this study, the multiscale structural changes of plasma-sprayed TBCs co-induced by strain and sintering were investigated. It is found that the overall evolution can be divided into several stages. At stage I, the single effect of strain leads to similar microscopic structural changes, despite of positive or negative CTE mismatch. This is highly related to the feature of lamellar structure. At stage II, the co-effect of sintering and strain on microscopic structural change is associated with the strain signs. Different strain signs lead to opposite changing trends in morphology of inter-splat pores, which affects their healing rates through multi-contact. As a result, the positive strain would enhance the sintering kinetic, whereas the negative strain would retard the sintering kinetic. At stage-III, the co-effect of sintering and strain leads to macroscopic structural changes, which can be responsible for different failure mechanisms. The new insight into co-effect of sintering and strain provides a comprehensive understanding on the performance evolution of plasma-sprayed TBCs, which is crucial for the further structural tailoring to retard the performance degradation.