Degradation of free-standing air plasma sprayed CoNiCrAlY coatings by vanadium and phosphorus pentoxides

Use of alternative and/or low-cost fuels such as syngas, petcoke and coal/petcoke blend in gas turbine engines requires a thorough understanding in high temperature degradation of protective coatings. Deleterious combustion by-products can deposit, adhere, melt and degrade the protective coatings and underlying structural substrates. In this investigation, degradation of air plasma sprayed (APS) free-standing CoNiCrAlY coatings in contact with two different corrosive oxide contaminants, namely V(2)O(5) and P(2)O(5) were examined at high temperature. Different degradation mechanisms were observed from V(2)O(5) melt interaction with CoNiCrAlYat 700 degrees C and 900 degrees C. At 700 degrees C, formation of chromium-aluminum orthovanadate (CrAl)VO(4) was observed with no evidence of severe degradation. However, at 900 degrees C, extensive dissolution of CoNiCrAlY constituents by V(2)O(5) Was found with reaction products such as nickel-cobalt orthovanadate (Ni,CO)(3)(VO(4))(2) and (Ni,Co)(Al,Cr)(2)O(4) spinel. Interaction of P(2)O(5) melt with CoNiCrAlY at 350 degrees C for 2 h revealed the extensive consumption of constituents through formation of polyphosphate compounds such as (Ni,Co)(PO(3))(2) and (Cr, Al)(PO(3))(3). (C) 2008 Elsevier B.V. All rights reserved