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Influence of regeneration treatments on creep rupture lifes of turbine blades

: Wortmann, J.; Busch, W.-B.

Marriott, J.B.; Merz, M.; Nihoul, J.; Wards, J.:
High temperature alloys. Their exploitable potential
London, 1988
ISBN: 1-85166-174-3
Aufsatz in Buch
Fraunhofer IFAM ()
creep rate; creep rupture life; creep voids; fracture probability; hot isostatic pressing; microstructure; Nimonic 108; regeneration treatment

The turbine blades in aircraft engines are subjected to a complex combination of stresses. With hot-gas temperatures of 1700 K, centrifugal accelerations of about 2000,000 g and outside to inside temperature gradient of 150 K/mm in efficiently cooled blades. Life limiting mechanisms are high cycle fatigue, low-cycle fatigue or thermal fatigue damage. Creep mechanisms, superimposed and accompanied by hot-gas corrosion are activated during steady state conditions. In general, structural changes occur under the effects of temperature, time and stress. Creep void formation under conditions of vacancies, resulting from climbing of dislocations around -particles. The voids start to form relatively early in the secondary stage of creep. After regeneration, the life of specimens, which had all reached the tertiary stage of creep was at least 75% of that of virgin specimens. The agreement of the minimum creep rates before and after rejuvenation can be taken as an indication that the structure c an be largely restored to its initial configuration since the minimum creep rate strongly depends on the structural parameters. Regeneration by HIP-ing has been shown to be usable for certain applications, provided that the life consumption due to service is caused by voids which are not surface connected. This means that any application of a regeneration treatment by HIP-ing must be investigated closely for the mechanisms acting during creep-life consumption.