Synthesis and cyclic oxidation behavior of a (Ni, Pt) Al coating on a desulfurized Ni-base superalloy
- PDF / 1,151,794 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 53 Downloads / 184 Views
I. INTRODUCTION
STATE-OF-THE ART thermal barrier coatings (TBCs) consist of a strain-tolerant Y2O3-stabilized-ZrO2 (YSZ) layer prepared by electron beam–physical vapor deposition (EB– PVD) and an underlying metallic bond coat (nickel aluminide, platinum aluminide, or NiCoCrAlY), which provides oxidation protection to the superalloy substrate by forming a protective Al2O3 scale. The dominant failure mode observed in this coating system is progressive fracture along the interface between the bond coat and the thermally grown oxide scale during normal engine operation.[1,2,3] From this perspective, the development of bond coats with improved Al2O3 scale adhesion is a critical issue in the design of more reliable TBC systems. The beneficial effects of sulfur removal on the oxidation resistance of superalloys have been relatively well documented.[4–7] It has been clearly shown that, for yttrium-free Ni-based alloys, the removal of sulfur impurities to below ,1 ppmw increases Al2O3 scale adhesion to a level comparable to that achieved with typical reactive element doping.[8,9] Our previous work[10] demonstrated that reducing the sulfur content of NiAl coatings fabricated by chemical vapor deposition (CVD) significantly improved Al2O3 scale adhesion during cyclic oxidation at 1150 8C, although preferential scale spallation eventually occurred along the aluminide coating grain boundaries. Furthermore, it has also been demonstrated that the lifetime of a commercial EB–PVD TBC Y. ZHANG, formerly Graduate Student, Department of Materials Science and Engineering, University of Tennessee, is with Walbar Metals, Peabody, MA 01960. W.Y. LEE, Associate Professor, is with the Department of Materials Science and Engineering, Stevens Institute of Technology, Hoboken, NJ 07030. J.A. HAYNES, I.G. WRIGHT, and B.A. PINT, Research Staff Members, and K.M. COOLEY, Engineering Technician, are with the Oak Ridge National Laboratory, Oak Ridge, TN 37831. P.K. LIAW, Professor, is with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996. Manuscript submitted December 7, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
system with a (Ni, Pt)Al bond coat can be improved by desulfurizing the superalloy substrate.[11,12] Platinum incorporation in aluminide coatings has been used for over 30 years to improve both hot corrosion and oxidation resistance.[13,14] Extensive work has focused on platinum aluminide coatings fabricated by pack cementation or CVD, both of which result in a surface layer of either PtAl2 or [PtAl2 1 (Ni, Pt)Al].[14,15,16] More recently, a lowactivity platinum aluminide coating that exhibits a surface layer of single-phase (Ni, Pt)Al, instead of PtAl2 or [PtAl2 1 (Ni,Pt)Al], has been developed via CVD processing[17,18] There has been limited evaluation of this new single-phase platinum aluminide coating, but initial results indicate improved cyclic oxidation behavior, hot corrosion resistance, thermal stability, and ductility, as compared to conventional platinum aluminide coatings.
Data Loading...
