Characterization of microstructures containing abnormal grain growth zones in alloy 718

A well known issue encountered by forgers transforming alloy 718 consists in the appearance of coarse grain zones during the thermo-mechanical process. Although some industrial solutions have been implemented in order to get rid of this type of microstructural defect, the consequences of the presence of such coarse grained areas on the material’s mechanical properties are of great interest. In this work, some zones that have undergone Abnormal Grain Growth (AGG) have primarily been characterized from a microstructural point of view by means of both optical and EBSD observations. Special attention has been paid to grain orientation, grain boundaries and grain size distributions. In addition the effects of these microstructures on 350°C deformation controlled fatigue crack initiation mechanisms and the subsequent lifetime have been assessed as well as on 350°C tensile properties have also been evaluated. The results will be discussed with regard to microstructure/mechanical behavior relationships. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.