The evolution of thermal barrier coatings - status and upcoming solutions for today's key issues

Thermal barrier coating applications have been used on thermally loaded combustion process components for decades. In the beginning of turbine technology development, science and industry worked on solutions about how to combine different properties such as those of superalloy metals and ceramic insulators. While partially stabilized zirconia became the standard material very early on, thermal spraying and electron beam physical vapor deposition in the early 1990s were even considered as competing technologies. This paper reviews why EB-PVD is the actual choice for the latest state-of-the-art components. Although EB-PVD coatings have a higher thermal conductivity than plasma-sprayed coatings, especially for parts in the HP stage of the turbine, they have a longer life and are statistically more reliable. The major roadblocks for thermal barrier technology on its way to become a fully prime reliant, designed-in feature are the understanding and modeling of failure mechanisms and consequently to prove the developed lifing-models by testing and ultimately real component performance. Several potential answers for today's technical issues are discussed with respect to their ability to shift TBC applications to the next level of reliability within various engine environments. For example, the inline hardware concept offers a unique combination of conservative, proven process sequence steps with widely improved quality aspects and optimized throughput set-ups. (C) 1999 Elsevier Science S.A. All rights reserved.