A critical assessment of the mechanistic aspects in Haynes 188 during low-cycle fatigue in the range 25 C to 1000 C
- NASA-Lewis Research Center, Cleveland, OH (United States)
- NYMA, Inc., Cleveland, OH (United States)
A cobalt-nickel-chromium-tungsten alloy, Haynes 188, is currently used in many military and commercial aircraft turbine engines for combustor liners and for the liquid oxygen posts in the main injector of the space shuttle main engines. The low-cycle fatigue (LCF) behavior of Haynes 188 has been investigated over a range of temperatures between 25 C and 1,000 C employing a triangular waveform and a constant strain amplitude of {+-}0.4 pct. Correlations between macroscopic cyclic deformation and fatigue life with the various microstructural phenomena were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the crack initiation and propagation modes, deformation substructure, and carbide precipitation. Cyclic stress response varied as a complex function of temperature. Dynamic strain aging (DSA) was found to occur over a wide temperature range between 300 C and 750 C. In the DSA domain, the alloy exhibited marked cyclic hardening with a pronounced maximum at 650 C. Toward the end of the DSA domain, dislocation pinning by M{sub 23}C{sub 6} precipitates occurred predominantly. The deformation behavior below and above the DSA domain has also ben investigated in detail. The temperature dependence of LCF life showed a maximum at {approx}300 C. The drastic reduction in life between 300 C and 850 C has been ascribed primarily to the deleterious effects of DSA on crack initiation and propagation, while the lower life at temperatures less than 200 C has been attributed to the combined influence of low ductility and larger cyclic response stress.
- OSTI ID:
- 474119
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 28, Issue 2; Other Information: PBD: Feb 1997
- Country of Publication:
- United States
- Language:
- English
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