Abstract: The cracking behavior of the top coat (TC) during fabrication is closely associated with its microstructures and characteristics in air plasma sprayed thermal barrier coating systems (APS-TBCs). In this study, the evolution and competition between two major cracking behaviors, namely segmental cracking and interfacial cracking, are investigated during the continuous deposition process of TC. By experimentally measuring the peak quenching stress of TC and theoretically calculating the propensity for both cracking behaviors, the competition between both behaviors is revealed. The experimental and theoretical results demonstrate that the propensity for both cracking behaviors increases with increasing peak quenching stress, however, their competition leads to a decreased propensity for each other. A reduction in surface crack density caused by interfacial cracking occurs once the threshold value for interfacial cracking is satisfied. Furthermore, regulation of interfacial cracking behavior is achieved by adjusting the interfacial bonding strength at the TC-BC interface, enabling the fabrication of segmented APS-TBCs with a controllable surface crack density over a wider range of peak quenching stress. The conclusions drawn in this article provide a better understanding of the competition between segmental cracking and interfacial cracking during plasma spraying process and offer guidance for fabricating APS-TBCs with desired crack patterns.

Key words: Thermal barrier coating, Plasma sprayed coatings, Segmental cracking, Interfacial cracking, Surface cracks