The typical combustion chamber gas path requires a Thermal Barrier Coating (TBC), which performs the important function of insulating and protecting the parent metal from the severe heat load. Effusion hole air-cooling systems are used in conjunction with TBC to achieve maximum benefit by reducing the thermal gradients in the metallic substrate. This greatly reduces the driving force of thermal fatigue. Combustion chamber durability is improved dependent upon the integrity of the TBC ceramic insulation layer.
The current industry method used to produce effusion air-cooling holes in TBC-coated combustion chambers requires laser drilling through the metallic substrate and the TBC. Unfortunately, laser drilling generates significant fracture energy in the TBC, which results in TBC debonding, delamination and subsequent TBC loss. This, of course, adversely affects component durability and service life.
To solve this problem, we developed the TCT BLAST™, a proprietary process which enables TBC ceramic insulation to be applied after laser drilling of effusion air-cooling holes, thereby eliminating the laser damage which occurs from laser drilling through the TBC ceramic insulation layer.
There is also an additional benefit of this process. The metallic substrate air-cooling hole surfaces and edges are smoothed and rounded during the TCT BLAST™ process. This significantly improves the airflow characteristics of the air-cooling holes by increasing the hole Cd (discharge coefficient). Rigorous OEM testing (furnace cyclic and accelerated mission) has validated and verified the durability improvement which can be realized by using TCT BLAST™ process technology for manufacture and repair applications.