Short term precipitation kinetics of delta phase in strain free Inconel 718 alloy

Understanding and control of short term precipitation of delta phase in Inconel 718 alloy is of importance as it is used to control grain growth during forging. This precipitation has been studied on both as received and solution treated 718 alloy, in the temperature range 650 to 1020degreesC and for times up to 10 h. The outer envelope of the transformation -time -temperature (TTT) diagram, which indicates the time at which the delta phase first precipitates during isothermal holding at a given temperature, has been drawn and compared to a critical review of previous information. Precipitation kinetics are also reported for both materials and discussed in the light of the very scarce data available in the open literature. According to these results, the so called 'nose' of the TTT diagram is located at a higher temperature and lower time than predicted from previously published diagrams.