Ni-Fe-base superalloy 706 has recently been used for high temperature services. A stabilizing treatment between solution-annealing and agehardening treatments has been proposed for this alloy to improve its creep rupture life. However, the relationship between stabilizing treatment and precipitation behavior has not been well understood. The precipitation behavior of Alloy 706 was investigated and related with creep rupture properties. Samples taken from a gas turbine disk forging were solution-treated at 980°C for 3h and stabilizing-treated in a range of 780 to 900°C for 1.5 h, followed by the double-aging at 720°C for 8h and at 620°C for 8h. Precipitation behavior of these samples was examined by TEM, and creep rupture tests were conducted at three conditions with varying temperature and applied stress.Fine Y'-~" co-precipitates having the core of y ' being overlayed with y " on its top and/or bottom and large y ' -y ' co-precipitate having the core of y ' being completely covered with y " were identified in the grain matrix together with large y ' and fine y It phases that have been found to precipitate in Alloy 706. 7 was identified at the gram boundary and found to be accompanied with a serrated grain boundary and denuded zone. Such precipitation behavior was significantly affected by stabilizing temperature, especially below 840°C. and so was creep rupture property accordingly. It is concluded that the best creep rupture properties are obtained when an optimum combination is established between intragranular fine y '/ y " co-precipitates, intra-granular large y '/ y " co-precipitates, and the inter-granular 7 phase.

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Ni-Fe-base superalloy 706 has been used for high temperature services.The time -temperature -precipitation (TTP) diagram is essential in the design of heat treatments for any precipitation strengthened superalloy.The TTP diagrams have been already presented for Alloy 706. However, effects of aluminum, titanium and niobium, important substitutional elements of y ' and y " precipitates, on the TTP behavior are not clear in the literature.In this study, the TTP and the time -temperature -hardness (TTH) diagrams are presented for experimental alloys containing only one or two of Ti, Nb and Al, in a temperature range of 600 -900°C. The observation by optical microscopy, scanning electron microscopy and transmission electron microscopy revealed that y ' , y ", y '-y " co-precipitates and 17 form in alloys containing Ti.Among the three elements, Ti plays the most important role in the precipitation strengthening behavior of Alloy 706. Furthermore, neither Al nor Nb can demonstrate their effects without Ti addition. Nb promotes y " formation and prevents 7 formation. Al enhances the formation of stable y '-y " co-precipitates, more effectively in the co-existence of Ti and Nb.