Continuously increasing hot gas temperatures in heavy duty gas turbines lead to increased thermal loadings of the hot gas path materials. Thermal barrier coatings are used to reduce the superalloys temperature and cooling air needs. Until now 6-8 wt% yttria stabilized zirconia is the first choice material for such coatings, but it is slowly reaching its maximum temperature capability due to the phase transformation at high temperature and sintering.
New thermal barrier coating material with increased temperature capability enable the next generation of gas turbine with >60% combined cycle efficiency. Such material solutions have been developed through a multi-stage selection process. In a first steps, critical material performance requirements for thermal barrier coating performance have been defined based on the understanding of standard TBC degradation mechanisms. Based on these requirements, more than 30 materials were a pre-selected and evaluated as potential coating materials. After carefully reviewing their properties both from literature data and laboratory test results on raw materials, five materials were selected for coating manufacturing and laboratory testing.
Based on the coating manufacturing trials and laboratory test results, two materials have been selected for engine testing, in a first step in GT26 Birr Test Power Plant and afterwards in customer engines. For such tests the original coating thickness has been increased such to achieve coating surface temperature ~100K higher than with a standard thermal barrier coating. Both coatings performed as predicted in both GT26 Birr Test Power Plant and customer engines.