Thermal barrier coating systems and processes therefor

A process of forming a coating system on a component, the process comprising:

• depositing a bond coat on a surface of the component;
• depositing an inner ceramic layer on the bond coat using a thermal spray process to yield a microstructure characterized by splats and horizontal porosity, the inner ceramic layer consisting essentially of zirconia stabilized by about 6 to about 9 weight percent yttria and being deposited to have a thickness and a porosity level;
• depositing an outer ceramic layer on the inner ceramic layer using a thermal spray process to yield a microstructure characterized by splats and horizontal porosity, the outer ceramic layer defining an outermost surface of the coating system and consisting essentially of zirconia stabilized by about 25 to about 75 weight percent yttria, the outer ceramic layer being deposited to have a thickness that is less than the thickness of the inner ceramic layer and have a porosity level that is higher than the inner ceramic layer;
• and then
• heat treating the inner and outer ceramic layers in a vacuum to a temperature and for a duration sufficient to relieve stresses therein induced by the depositing steps.