Isothermal fatigue of an aluminide-coated single-crystal superalloy. Part 2: Effects of brittle precracking

Journal Article · Thu Feb 01 04:00:00 EST 1996 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02648413· OSTI ID:207686

Totemeier, T C; King, J E ^[1]; Gale, W F ^[2]

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1. Univ. of Cambridge (United Kingdom). Dept. of Materials Science and Metallurgy
2. Auburn Univ., AL (United States). Materials Engineering Program

The effect of brittle coating precracking on the fatigue behavior of a high-activity aluminide-coated single-crystal nickel-base superalloy has been studied using hollow cylindrical specimens at test temperatures of 600 C, 800 C, and 1,000 C. Three types of precrack were studied: narrow precracks formed at room temperature, wide precracks formed at room temperature, and narrow precracks formed at elevated temperature. The effect of precracking on fatigue life at 600 C was found to depend strongly on the type of precrack. No failure was observed for specimens with narrow room-temperature precracks because of crack arrest via an oxidation-induced crack closure mechanism, while the behavior of wide precracks and precracks formed at elevated temperature mirrored the non-precracked behavior. Crack retardation also occurred for narrow room-temperature precracks tested at 800 C--in this case, fatigue cracks leading to failure initiated in a layer of recrystallized grains on the inside surface of the specimen. A significant reduction in fatigue life at 800 C relative to non-precracked specimens was observed for wide precracks and elevated temperature precracks. The presence of precracks bypassed the initiation and growth of coating fatigue cracks necessary for failure in non-precracked material. No effect of precracking was observed at 1,000 C.

• Sponsoring Organization: USDOE
• OSTI ID: 207686
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 2 Vol. 27; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CRACKS
DUCTILE-BRITTLE TRANSITIONS
FATIGUE
NICKEL BASE ALLOYS
OXIDATION
PROTECTIVE COATINGS
STRAINS
SURFACE COATING
TEMPERATURE DEPENDENCE
TIME DEPENDENCE