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THERMAL FATIGUE OF MAR‐M509 SUPERALLOY—I. THE INFLUENCE OF SPECIMEN GEOMETRY
Author(s) -
RezaiAria F.,
François M.,
Rémy L.
Publication year - 1988
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.1988.tb01181.x
Subject(s) - materials science , superalloy , thermal fatigue , wedge (geometry) , metallography , metallurgy , carbide , isothermal process , temperature cycling , microstructure , atmospheric temperature range , thermal , composite material , geometry , mathematics , meteorology , thermodynamics , physics
— The thermal fatigue behaviour of a cast cobalt superalloy was investigated. Wedge type specimens were tested on a rig using flame heating. A standard cycle from 200 to 1100°C was used for most tests and the specimen geometry was changed to investigate a broad range of thermal fatigue lives. The maximum temperature was also varied for a single specimen geometry. The thermal fatigue life to create a 1 mm deep crack ranges from a few tens to one thousand cycles. Crack initiation occurs early in life at oxidised interdendritic carbides as in high‐temperature, low‐cycle fatigue. Precipitation of small chromium‐rich carbides was found to occur in the dendrites during thermal fatigue cycling. An identical precipitate distribution could be induced by a two stage thermal treatment as shown by quantitative metallography. The isothermal stress‐strain behaviour at high temperature was so shown to be almost insensitive to the microstructure changes induced by thermal fatigue.