Observations of Static Strain-Aging in Polycrystalline NiAl

Static strain-aging has been investigated in eight polycrystalline NiAl alloys. After annealing at 1100 K for 7200 s followed by furnace cooling, high-purity, nitrogen-doped, and titanium-doped alloys exhibited continuous yielding, while conventional-purity and carbon-doped alloys exhibited distinct upper yield points and Luders strains. Either water quenching from 1100 K or prestraining via hydrostatic pressurization suppressed the yield points in the latter alloys, but they could be reintroduced by further annealing treatments. Yield points could be reintroduced more rapidly if the specimens were prestrained uniaxially rather than hydrostatically, owing to the arrangement of dislocations into cell structures during uniaxial deformation. Chemical analysis suggests that the species responsible for strain-aging is interstitial carbon