STRESS-RELAXATION IN PRECIPITATION-HARDENABLE ALLOYS

Sensitive stress relaxation measurements of the precipitation-hardenab le alloys CuBe2, Nimonic PE16, Nimonic 105 and solid-solution Alloy 82 5 have been performed in order to minimize the relaxation effects. In all samples, part of the stress relaxation fades away after plastic de formation or heat treatment over several days. So the relaxation stren gth itself shows an effect of recovery. In CuBe2 the change in stress relaxation can be explained because precipitates lower the free segmen t length of mobile dislocations and because of the depletion of Be sol id solutes. At about 300 degrees C, ordering effects in the nickel all oys Nimonic PE16 and Alloy 825 correlate with stress relaxation. In Ni monic PE16 and Nimonic 105, precipitation occurs at 650 degrees C and 700 degrees C respectively and affects the stress relaxation strength. All effects including the slowly ascending stress relaxation curves c an be explained by a dislocation mechanism with involved solid solutes .