Strengthening and Nanostructure of Metals and Alloys
The detrimental effects of precipitate free zones on the yield strength of polycrystals of the commercial
nickel-base superalloy NIMONIC PE16, which is strengthened by nano-scale precipitates of the g'-phase
The dispersion of nano-scale g'-precipitates and the width w of g'-precipitate free zones (PFZ) along grain boundaries have been varied systematically
for the commercial nickel-base superalloy NIMONIC PE16. This material serves as a model system in a general
study of the effects of PFZs. The yield strength sy was found to
decrease as w increases provided w exceeds a minimum value. The maximum observed decrease of
sy amounts to 25%. The technical relevance of this effect is
evident. The dislocation processes in the PFZs have been studied by stretching thin foils inside a transmission
electron microscope and observing the glide of dislocations under full load. Softening due to PFZs is mainly
caused by the ease with which dislocations are created in the PFZs; this leads to concentrated slip. Attempts to
eliminate the detrimental effects of PFZs by double aging treatments failed.
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