methods a by means of hf gas phase in a fluoride ion cleaning fic installation an installation of this type and the processes which it can be used to carry out are disclosed for example in us a1 2002 157277 b by means of hydrofluoric acid solution in vapor form for example in an autoclave c by means of aqueous hydrofluoric acid solution in a chemical bath d by means of mild shot peening of the tbc coated surface if appropriate in combination with smoothing of the tbc e by means of the trowal in combination with smoothing of the tbc f by means of infiltration of a liquid which on solidification weakens the microcontacts on account of a volumetric expansion in this context the process used should be selected in such a way that the tgo 13 is not attacked and the adhesion to the bond coat 12 remains unaffected the sio 2 that is present as an impurity at the inner surface of the tbc as well as further oxidic impurities which are significantly involved in the progressing sintering process are selectively decomposed destabilization of the partially stabilized y 2 o 3 zro 2 crystal bulk is avoided the tbc layer thickness remains substantially unchanged and damage to regions that are not tbc coated blade or vane interior and regions with a metallic protective coating is avoided the invention can in general terms be employed in regions in which the tbc flakes off prematurely and this has the effect of limiting service life or.