Isothermal fatigue of an aluminide-coated single-crystal superalloy:Part I

Totemeier, T.C. and King, J.E. Isothermal fatigue of an aluminide-coated single-crystal superalloy:Part I. Metallurgical and Materials Transactions A, 27 (2), pp. 353-361.

Abstract

The isothermal fatigue behavior of a high-activity aluminide-coated single-crystal superalloy was studied in air at test temperatures of 600 °C, 800 °C, and 1000 °C. Tests were performed using cylindrical specimens under strain control at ∼0.25 Hz; total strain ranges from 0.5 to 1.6 pet were investigated. At 600 °C, crack initiation occurred at brittle coating cracks, which led to a significant reduction in fatigue life compared to the uncoated alloy. Fatigue cracks grew from the brittle coating cracks initially in a stage II manner with a subsequent transition to crystallographic stage I fatigue. At 800 °C and 1000 °C, the coating failed quickly by a fatigue process due to the drastic reduction in strength above 750 °C, the ductile-brittle transition temperature. These cracks were arrested or slowed by oxidation at the coating-substrate interface and only led to a detriment in life relative to the uncoated material for total strain ranges of 1.2 pet and above 800 °C. The presence of the coating was beneficial at 800 °C for total strain rangesless than 1.2 pet. No effect of the coating was observed at 1000 °C. Crack growth in the substrate at 800 °C was similar to 600 °C; at 1000 °C, greater plasticity and oxidationrwere observed and cracks grew exclusively in a stage II manner.

Publication DOI: https://doi.org/10.1007/BF02648412
Divisions: Aston University (General)
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Uncontrolled Keywords: aluminum alloys,brittle fracture,coated materials,biocompatible,crack initiation,crack propagation,fatigue of materials,fatigue testing,interfaces (materials),intermetallics,oxidation,single crystals,strain control,aluminide coated single crystal superalloy,crystallographic stage I fatigue,isothermal fatigue,superalloys,Materials Science(all),Metals and Alloys

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