Rr. Stephens et al., THE EFFECT OF TEMPERATURE ON THE BEHAVIOR OF SHORT FATIGUE CRACKS IN WASPALOY USING AN IN-SITU SEM FATIGUE APPARATUS, International journal of fatigue, 15(4), 1993, pp. 273-282
Short fatigue crack growth behaviour was studied in Waspaloy at 25-deg
rees-C, 500-degrees-C and 700-degrees-C under cyclic loading condition
s at a stress ratio of 0.1. Specimens were tested within an elevated t
emperature fatigue apparatus coupled to a scanning electron microscope
which allowed in situ observations to be made of the fatigue process.
Crack formation was dominated by slip band cracking at 25-degrees-C a
nd 500-degrees-C, while at 700-degrees-C cracks formed along slip band
s and twin boundaries. Crack propagation proceeded by means of slip ba
nd cracking at 25-degrees-C and 500-degrees-C, while at 700-degrees-C
crack growth was primarily stage 11-mode I type growth. Short fatigue
crack growth rates were faster at 500-degrees-C than at 25-degrees-C f
or an equivalent stress intensity range, DELTAK(I), owing to a change
in slip character. Short crack growth rates tended to be lower at 700-
degrees-C than at 500-degrees-C, owing to changes in the material lead
ing to precipitate coarsening. As the temperature was increased, micro
structural contributions to crack growth decreased, resulting in a red
uced microstructural short crack effect.