Utilização dos ensaios de ultrassom e correntes parasitas no acompanhamento da oxidação em revestimentos TBC com NiCrAl e YSZ sobre liga de Inconel 718 e Hastelloy X

Abstract

This paper presents an evaluation of the use of non-destructive methods with ultrasound and eddy currents, monitoring of life and characterization of thermal barrier coatings (TBC). This coatings are used to protect base metal components that operate at high temperatures. With the method that uses the ultrasonic characterization of ceramic layer was made an estimating their porosity through the sound propagation of velocity in the coating. The test with eddy currents was used here to make an electrical characterization of materials coated, following the changes of electrical conductivity through the phase angle monitoring following their lifecycle. Also with this method are made the measurements of coatings thickness, following the growth of the thermally grown oxide layer and sintering of the ceramic layer. To validate the results obtained by non-destructive methods, these results were compared with results from analyzes micrograph of the samples used. For evaluation of pre-oxidation in the sample coatings were separated into two groups based metal Inconel 718 and Hastelloy X base metal. The group of samples with Inconel 718 when subjected to the oxidation test showed the formation of an alumina layer up to 30 cycles of the testwith the passing of the cycles were formed oxides of nickel and chromium which grew quickly leading the coating to the cracks. The samples of Hastelloy X in substrate oxidation test showed predominantly alumina to form up more than one layer of the same oxide no showed oxides of nickel and chromium, and no cracks in the test sample are showed in TBC layer. The use of non destructive testing has shown effective to follow the life cycle of TBC coatings. Where the monitoring of variations in thickness, showed little difference in value with respect to measurements metallographic method. The reading of electrical conductivity through the phase angle is a good indicator of formation of harmful oxides which were nickel and chromium oxides, which was evidenced by tests on MEV/EDS. It was observed that the ultrasound velocity has an inversely proportional relation to the porosity of the ceramic layer, that analyzed using metallographic method.