Differential Thermal Analysis (DTA) Study of the Homogenization Process in Alloy 718

Abstract

The DTA thermograms of as-cast and homogenized Alloy 718 have been determined. In combination with the results of an interrupted melting experiment, it was found that the incipient melting temperature (solidus) of as-cast alloy was about 1165 0 C and homogenization increased the incipient temperature of Alloy 718 to about 1230 o C for a fully homogenized alloy. An endothermic peak was found at about 1290°C for homogenized alloys in contrast with a slight inflection in as-cast alloys at the same temperature. A special melting experiment below, at, and above the inflection temperature around 1290 0 C showed that this peak was associated with the dissolution of NbC/y eutectic in cast alloy and carbide: particles in homogenized alloys instead of the melting of bulk y matrix. The monovariant NbC/y eutectic reaction occurred over the temperature range from 1260 OC to 12970 C (as-cast) and carbide dissolution from 1267 o C to 1305 o C (homogenized). Superalloys 718,625 and Various Derivatives Edited by Edward A. Lmia The Minerals, Metals & Materials Society, 1991