**Preface to "Science and Technology of Thermal Barrier Coatings"**

Globally, higher efficiency in thermal conversion process has been required to satisfy the growing demand for reducing the consumption of fossil fuels. The higher operating temperature of gas turbines results in enhanced thermal conversion efficiency and has been achieved via advances in various techniques, such as superalloy, cooling technology, and thermal barrier coating (TBC). Among them, TBC exhibits promising potential to achieve the enhanced energy efficiency without limitations of material selection or efficiency reduction. However, TBCs are exposed to very harsh and complex operating conditions with high-speed rotation and high-temperature flame, requiring the consideration of various environmental factors. The yttria-stabilized zirconia (YSZ) has been governed by the TBC field, but it is limited at higher operating temperatures above 1200 °C due to phase degradation and poor sintering resistance. A grea<sup>t</sup> deal of effort has been devoted to overcoming the limitations of YSZ through various attempts, such as doping YSZ with various metal oxides, and applying new materials like zirconates and perovskites. Nonetheless, there are still many complicated application limitations that should be tackled in this field and in response, we have focused this Special Issue of Coatings on emerging efforts in developing novel TBC materials and their comprehensive reliability against the complex environmental factors.

Contributions to this Special Issue include original papers covering the development of advanced TBCs and their reliability, which improve the lifetime performance. In particular, Kilic et al. [1] investigated the microstructural characteristics and wear behaviors of the CoNiCrAlY-based metallic bond coat using the novel methods, D-gun and supersonic plasma spraying. Ctibor et al. [2] fabricated SrZrO3 TBC via water-stabilized plasma and revealed its corrosion interaction mechanism with natural silicate dust. Lu et al. [3] evaluated the lifetime performance TBC with different bond coat species and top coat which deposited by electron beam-physical vapor deposition. Cheng et al. [4] revealed the thermal stability of YSZ TBC fabricated via novel plasma spray-physical vapor deposition method. Zeng et al. [5] studied the high temperature anti-friction behaviors of Si–H film. Song et al. [6,7] investigated the crack-growth behavior during cyclic thermal exposure and revealed the crack-resistant behavior of TBC with an encapsulated healing agent-embedded buffer layer. Liu et al. [8] evaluated the hot corrosion behavior of BaLa2Ti3O10 TBC and elucidated its corrosion reaction mechanism. Orosa et al [9] reported a novel method of nearly zero energy building internal covering design based on the neural networks. Finally, Chang et al. [10], first evaluated the contributions of high thermomechanical fatigue on gas turbine lifetime during a steady-state operation.

In summary, this Special Issue provides an overview of the development of advanced TBCs to improve comprehensive reliability, which could potentially be applied in hot components of advanced gas turbine. As such, I hope that this Special Issue is a forum to highlight and identify emerging research in the field.
