Accession Number : ADA112342

Title :   Dip Process Thermal Barrier Coating for Superalloys.

Descriptive Note : Annual rept. 14 Dec 80-14 Dec 81,

Corporate Author : SRI INTERNATIONAL MENLO PARK CA

Personal Author(s) : Allam,I M ; Rowcliffe,D J

PDF Url : ADA112342

Report Date : 02 Feb 1982

Pagination or Media Count : 57

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)

Descriptors :   *Superalloys, *Coatings, *Barriers, *Thermal insulation, Processing, Cerium compounds, Oxides, Annealing, Dip coating, Layers, Cracks, Spallation, Cobalt alloys, Melts, Oxidation, Cyclic tests, Chemical composition, Nickel, Hot working

Subject Categories : Polymer Chemistry
      Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE