SEDL / STP / STP942-EB / STP24514S

Thermal Fatigue Testing of Coated Monocrystalline Superalloys

Holmes, JW
Graduate Student, Massachusetts Institute of Technology, Cambridge, MA

McClintock, FA
Professor and Undergraduate Student, Massachusetts Institute of Technology, Cambridge, MA

O'Hara, KS
Metallurgist, General Electric Company, Lynn, MA

Conners, ME
Professor and Undergraduate Student, Massachusetts Institute of Technology, Cambridge, MA

Pages: 20    Published: Jan 1988

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Abstract

Induction heating of stepped-disk specimens to study thermal fatigue of coated superalloys is well suited for studying anisotropic alloys and is easily adaptable for corrosive or inert atmosphere testing. Details of the experimental apparatus and results of a thermoelastic finite element analysis to find the stress-strain history are given.

To illustrate the technique, the effect of cyclic thermal strains on the durability of an aluminide coating applied to a typical monocrystalline nickel-base superalloy was studied in air. Results show that both the compressive strain encountered on specimen heatup and the tensile strain encountered on cooldown critically affect the aluminide coating degradation. After 6000 cycles of heating from 520 to 1080°C in 5 s, followed by 30 s cooling, 80% coating penetration by scalloping was observed. A similar treatment with 6 s cooling resulted in alumina-filled “cracks” extending into the substrate.