Dip Process Thermal Barrier Coating for Superalloys.
Abstract
A NEW, CERIUM OXIDE-BASE THERMAL BARRIER COATING FOR SUPERALLOYS HAS BEEN INVESTIGATED. Cerium oxide is promising as a thermal barrier because of its low thermal conductivity and its relatively high coefficient of thermal expansion, suggesting good compatability with superalloys. The coating is applied by hot-dipping superalloys substrates into a molten bath of low-melting cerium-nickel alloy. Annealing and selective oxidation of cerium at low oxygen activities produce a duplex coating of a continuous outer layer of cerium oxide (CeO2) and an inner composite cerium oxide/substrate layer. The effect of coating composition and processing variables on the micro-structure and integrity of the coating on nickel- and cobalt-base alloys was studied in detail. The best, thin, crack-free coatings were produced on MAR-M509 with a coating alloy of Ce-30% Ni. Isothermal and cyclic oxidation tests showed that coating spallation could occur and was associated with the oxidation of nickel and cobalt incorporated in the coating. A model for the formation of the CeO2 barrier and the subscale region is proposed that accounts for the presence of unwanted nickel and cobalt; methods for avoiding their presence are proposed. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 02, 1982
- Accession Number
- ADA112342
Entities
People
- D. J. Rowcliffe
- I. M. Allam
Organizations
- SRI International