NONDESTRUCTIVE EVALUATION OF THE OXIDATION STRESSES THROUGH THERMAL BARRIER COATINGS USING CR3+ PIEZOSPECTROSCOPY

The stresses in the aluminum oxide formed during high-temperature oxid ation of a bond-coated superalloy are shown to be measurable through z irconia thermal barrier coatings. The basis for the measurements is th e piezospectroscopic shift in the R-line fluorescence (photoluminescen ce) from Cr3+ impurities incorporated into the growing aluminum oxide scale. Measurements through the thermal barrier coating are feasible b ecause (partially stabilized) zirconia coating have some transparency at both the excitation and at fluorescence frequencies. (C) 1996 Ameri can Institute of Physics.