Identification of hot corrosion resistant MCrAlY based bond coatings for gas turbine engine applications

In the current paper, an attempt has been made to identify hot corrosion resistant coatings which can produce a thermodynamically stable and inert oxide scale during exposure to a hot corrosion environment and thereby enhance the coating life significantly. The results obtained from hot corrosion tests of a variety of MCrAlY-type coatings with different alloying elements and traces of silicon and hafnium in the presence of sodium chloride and vanadium containing environments revealed that a NiCoCrAlY coating exhibits maximum life time among the coatings studied. The results also revealed that presence of trace elements in the coating reduces coating life significantly. Based on the results, a novel electrochemical mechanism has been proposed. It has been shown that the hot corrosion of protective coatings is an electrochemical phenomena and hence the electrochemical techniques appear to be quite useful in evaluating coatings for hot corrosion resistance. (C) 2001 Elsevier Science B.V. All rights reserved.