Delta phase precipitation in Inconel 718

The precipitation and dissolution kinetics of the delta-phase were studied in three wrought versions and one spray-formed (SF) version of the nickel alloy, Inconel 718. The precipitation in the spray-formed version and one wrought version was followed during isothermal ageing for up to 100 h between 700 and 1000 degreesC. The delta-phase precipitates in the form of nonuniformly distributed thin platelets and an alternative method of measuring volume fraction of this precipitate morphology is proposed. At and above 800 degreesC, the precipitation was measured quantitatively in terms of the volume fraction and platelet thickness distribution. The maximum rate of precipitation occurred at approximately 900 degreesC. The solvus temperature lay between 1005 and 1015 degreesC for Nb contents of 5.06 and 5.41 wt.%, respectively. A study was made of the dissolution of the delta-phase in all four alloys using isochronal treatments and this confirmed the above solvus temperature range. The effect of delta-phase and its dissolution on the grain growth of the alloys was also determined. (C) 2004 Elsevier Inc. All rights reserved.