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RESEARCH PAPERS

Observations on the Interaction of High Mean Stress and Type II Hot Corrosion on the Fatigue Behavior of a Nickel Base Superalloy

[+] Author and Article Information
J. M. Allen

Westinghouse Combustion Turbine Systems Division, Concordville, Pa. 19331

G. A. Whitlow

Westinghouse Research and Development Center, Pittsburgh, Pa. 15235

J. Eng. Gas Turbines Power 107(1), 220-224 (Jan 01, 1985) (5 pages) doi:10.1115/1.3239686 History: Received January 09, 1984; Online October 15, 2009

Abstract

A study measuring the effects of a molten sulfate/chloride salt on the creep/fatigue behavior of a nickel base turbine blade superalloy, Udimet 720, at 1300°F (704°C) is described. Cyclic stress–cycles to failure (S-N) curves were generated at high mean stress levels, with mean stress, maximum stress, or the ratio of minimum to maximum stress (R ratio) held constant. In salt, it was found that when maximum stress is above the yield, with the cyclic component 20 percent of the maximum, failure occurs by stress corrosion fatigue in orders of magnitude less time than for corresponding loading conditions in air. It is significant, from a failure analysis point of view, that fatigue fracture is intergranular in these circumstances. Similar fatigue behavior may be expected for other nickel base alloys, however, at substantially lower maximum stresses in as much as Udimet 720 exhibits superior short time rupture strength, i.e., resistance to this form of stress corrosion, over the other blade alloys evaluated in this environment.

Copyright © 1985 by ASME
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