Potenzialità della tecnica EIS per il rilievo del degrado delle barriere termiche sottoposte a prove di ossidazione ciclica

This work consists in the study of the evolution of the typical coatings of hot parts in gas turbines, consisting in a metallic layer and a ceramic layer (zirconia partially stabilized with ittria), working as thermal barrier. First of all are showed the results of an experimental campaign performed on samples thermally cycled at two different temperatures and then examined with metallographic analysis to find the deterioration mechanisms due to exposure at high temperatures and the action of repeated thermal cycles. Then is considered the possibility of application of a non destructive evaluation technique (the electrochemical impedance spectroscopy) to detect the increasing level of deterioration. The variation of the obtained impedance spectra confirmed that the technique is sensitive to the thickness of the ceramic layer, to its characteristics (porosity and microcracking) and to the formation of the oxide layer at the metal-ceramic interface. The obtained results are discussed in the light of quantitative metallographic analysis and information available in the literature. Some further development lines are suggested.