Well-designed thermal barrier coatings are very essential in current industrial applications especially at elevated temperatures as they are effective protective layers. Their use has recently increased owing to their effectiveness leading to high component durability. Generally, thermal barrier coatings are made up of three layers: grown oxide layer, metallic bond coat and ceramic top coat which largely dictates the overall insulation performance as it acts as the thermal barrier. Among the available methods for preparing thermal barrier coatings, plasma spraying is the most widely used one due to its high deposition efficiency and cost-effective nature.
In addition, their thermal and mechanical properties are significantly lower than those of their corresponding materials, making them better thermal insulators. Unfortunately, thermal exposure results in the sintering of the top coat which lowers the strain tolerance and thermal insulation of thermal barrier coatings. Therefore, researchers have been looking for alternative methods to reduce the performance degradation initiated by sintering.
Taking advantage of recent advances in nanotechnology, plasma sprayed nanostructured top coats have been identified as promising candidates for enhancing the performance and durability of the thermal barrier coatings. For instance, recent studies have shown that nanostructured coatings formed by yttria-stabilized zirconia have a lower degradation degree and consequently a higher extended lifetime than conventional plasma sprayed yttria-stabilized zirconia coatings. However, the mechanisms responsible for the degradation-resistant behaviors of the nanostructured thermal barrier coatings have not been fully explored. Recently, bimodal structural evolution has been widely observed in the nanostructured coatings and, therefore, understanding it is an essential step in understanding the underlying mechanism responsible for the effective degradation-resistant behavior of the nanostructured thermal barrier coatings.
To this note, Xi’an Jiaotong University researchers: Dr. Guangrong Li and Professor Guanjun Yang explored the degradation-resistant behavior of plasma sprayed nanostructured bimodal thermal barrier coatings, and compared it to that of the conventional coatings. Specifically, nanostructured yttria-stabilized zirconia coatings were investigated. In addition, the author investigated the various changes in the microstructure and properties of the thermal barrier coatings. The work is published in Journal of Materials Science and Technology.
The authors commenced their research work by cross-examining the structural evolution of the nanostructured bimodal and conventional lamellar coatings. Next, they examined the sintering characteristics of both the nanozones and lamellar zones during thermal exposure to reveal the responsible mechanism for the degradation-resistant behavior. Eventually, they proposed structural tailoring for the realization of high-performance thermal barriers coatings.
In summary, Dr. Guangrong Li and Professor Guanjun Yang presented a better understanding of the degradation-resistant behavior of the nanostructured thermal barrier coatings. In general, nanozones and lamellar zones of the nanostructured thermal barrier coatings exhibited differential densification rates thus inducing the formation of coarse pores. These newly-formed pores cause counteractive effects against the healing of the microscopic two-dimensional pores. This led to the retardation of the performance degradation of bimodal thermal barrier coatings. Altogether, the study provided essential information that will lead to the realization of high-performance thermal barrier coatings.
Li, G., & Yang, G. (2019). Understanding of degradation-resistant behavior of nanostructured thermal barrier coatings with bimodal structure. Journal of Materials Science & Technology, 35(3), 231-238.Go To Journal of Materials Science & Technology