Degradation Mechanism Study of Selected Thermally Sprayed Coatings in the Environment of Steam Turbine

Abstract

In the paper, the influence of high temperature and hot pressure steam on the microstructure and phase composition of HVOF sprayed wear resistant Cr3C2-NiCr coating and flame sprayed NiCrAl-Bentonite abradable coating is studied. Both the results of laboratory oxidation tests and the long-term exposition tests in the steam turbine are presented. The mechanism of selective carbide oxidation was observed in both laboratory test and long-term oxidation test in the case of HVOF Cr3C2-NiCr coating. The oxidation of NiCrAl matrix of flame spray abradable coating is described. Both coatings suffered from oxidation, but their integrality was not disrupted even after 5.5 years of exposition in steam turbine environment.