ON THE MECHANISM OF SERRATED DEFORMATION IN AGED INCONEL-718

The serrated deformation of Inconel 718 alloy aged at 725 degrees C ib r various lengths of time has been studied in the temperature range fr om 200 to 575 degrees C and at constant strain rates in the range of 1 0(-2) to 5 x 10(-6) s(-1). It was observed that serrated flow in the a lloy depends on the interaction mechanism of dislocations with precipi tates. Normal serrated flow was observed when deformation occurred by dislocations cutting through precipitates. However,when the Orowan loo ping mechanism was operative in the overaged material, normal serrated flow was observed only when the strain rate was high or the test temp erature was low. In addition, the critical strain to serration was obs erved to increase with an increase in inter-particle spacing. This obs ervation is inconsistent with the models proposed by Hayes et al. and McCormick. Therefore, a new mechanism, which considers the specific in teraction mechanism of a moving dislocation with precipitates, has bee n proposed. (C) 1997 Elsevier Science S.A.