On the mechanism of serrated deformation in aged Inconel 718

The serrated deformation of Inconel 718 alloy aged at 725 degrees C ibr various lengths of time has been studied in the temperature range from 200 to 575 degrees C and at constant strain rates in the range of 10(-2) to 5 x 10(-6) s(-1). It was observed that serrated flow in the alloy depends on the interaction mechanism of dislocations with precipitates. Normal serrated flow was observed when deformation occurred by dislocations cutting through precipitates. However,when the Orowan looping mechanism was operative in the overaged material, normal serrated flow was observed only when the strain rate was high or the test temperature was low. In addition, the critical strain to serration was observed to increase with an increase in inter-particle spacing. This observation is inconsistent with the models proposed by Hayes et al. and McCormick. Therefore, a new mechanism, which considers the specific interaction mechanism of a moving dislocation with precipitates, has been proposed. (C) 1997 Elsevier Science S.A.