Cyclic high temperature oxidation of HFPD thermal sprayed CoNiCrAlY coatings under simulated gas turbine and furnace environments

Abstract

CoNiCrAlY powders were thermal sprayed using the high frequency pulse detonation (HFPD) method onto AISI 310 austenitic stainless steel samples. The cyclic oxidation behaviour of these coatings at 800 and 1000°C in simulated gas turbine and standard atmosphere environments was experimentally determined. Austenitic AISI 310 was used as a reference. Composition and morphology of surface phase were evaluated using X-ray diffraction and scanning electron microscope techniques. Oxidised HFPD CoNiCrAlY coatings have always been characterised by the formation of a continuous and highly protective alumina layer. In contrast, the protection of the chromium oxide layer generated on the austenitic AISI 310 under the same operating conditions is much less effective and a degraded region near to the oxidised layer has been observed at the highest temperatures. Moreover, cracks appear in the chromium oxide layer when it is submitted to high thermal gradients, as a consequence of thermal stresses.