Knowledge and control of the delta phase (Ni3Nb) solvus temperature is critical to optimize processing and heat treatment of alloy 718 for best mechanical properties. This is the case in aerospace applications where delta phase is used to produce fine grain structures during forging, and in oil-field applications where the delta phase is dissolved during solution treatment. Delta phase solvus is primarily controlled by niobium content. The effect of nickel content on delta phase solvus is not well understood as thermodynamic models and previous experiments have produced conflicting results. The purpose of this study was to confirm the effect of nickel content on delta solvus temperature using experimental heats and to document mechanical properties vs. nickel content. In addition, solvus results were compared with modeling predictions and an improved database was developed to more accurately predict delta phase solvus temperature in alloy 718. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.
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