Process for extending the cyclic service life of thermal barrier coatings, in particular on gas turbine components
View Patent ↗A process for extending the cyclic service life of thermal barrier coatings made of yttrium-stabilized zirconium oxide (YSZ) or the like which have been applied to a substrate with an oxidizing bond coat in between includes increasing or long-term stabilizing the strain tolerance of the thermal barrier coating.
1. A process for extending the cyclic service life of a thermal barrier coating, which includes microcracks bridged by punctiform contact locations and which is made of chemical thermal barrier coating composition applied to an oxidizing bond coat on a substrate, the process comprising:
infiltrating the thermal barrier coating by introducing water into pores in the thermal barrier coating by at least one of immersion, spraying, and gas phase infiltration;
freezing the water in the pores using liquid nitrogen or by dry ice to weaken the punctiform contact locations in the thermal barrier coating, thereby increasing a strain tolerance of the thermal barrier coating in comparison to the strain tolerance of a thermal barrier coating without the steps of infiltrating and freezing; and
removing the water from the pores by drying.
2. The process as recited in claim 1 , wherein a spatial propagation of the freezing step is controlled by targeted dissipation of heat into the substrate interior, so that a solidification front, starting from an interface of the thermal barrier coating and the oxidizing bond coat, is guided in a direction of the surface of the thermal barrier coating instead of closing off the pores from the outside before the solidification has ended to avoid decreasing the adhesion of the thermal barrier coating in comparison to the adhesion without the targeted dissipation of heat.