Degradation of Advanced MCrAIY Coatings by Oxidation and Interdiffusion

Abstract

The elemental depletion of MCrAlY coatings on IN 738 LC by interdiffusion and formation of Al 2 O 3 scales has been studied. Exposure experiments on a NiCoCrAlYRe coating with 12% Al and CoNiCrAl(8%)Y coating at 1000°C up to 10000 hours have been carried out. The total β-phase depletion and consequently the decrease of the Al content of the coating and the damage of the base material by interdiffusion was determined. Additionally the development of Kirkendall pores was found to increase with time. Of special interest were investigations on the interdiffusion behaviour on different elements after two different preheating temperatures (- 600°C, - 900°C) during the coating process itself. After the normal heat treatment for IN 738 LC, the element distribution in the coating and base material was unchanged at 600°C, but exhibited a 50μm interdiffusion zone at 900°C. With increasing preheating temperatures the adhesion strength is getting stronger and reach values larger than 200 MPa for a preheating temperature of 900°C. Therefore the bond strength is mainly controlled by the preheating prior to application of the coating.