Precipitate microstructure evolution in exposed IN738LC superalloy

Formation and Dissolution of γ’ Precipitates in IN792 Superalloy at Elevated Temperatures

“…Such behavior cannot be explained by simple models of strengthening, and rather complex model considering all relevant strengthening mechanisms should be used [6]. An interesting result for IN792-5A superalloy from an earlier study [19,20] was that it exhibits an anomaly in temperature dependence of the tensile properties in the temperature region 600-800 °C ( Figure 2). Nevertheless, it is well known that strength of polycrystalline superalloys often increases between room temperature and 800 °C [6].…”

“…When assuming volume fraction of precipitates to be 68% [18], then also the SLD of γ matrix can be calculated [4] with the result 58.3ˆ10 9 cm´2. The corresponding scattering contrast between γ´precipitates and γ matrix is then 8.5ˆ10 9 cm´2.…”

“…The aim was to ensure-for each T D -the same preconditions and thus the same microstructure of small precipitates at the beginning of the hold at T D temperature. The temperature 900˝C served (similarly as in the case of previous study with IN738LC [4]) for dissolution of all populations of small-and medium-size precipitates from the previous heat treatment steps. The annealing at 900˝C was thus a kind of "reset" of the precipitate microstructure-only large precipitates remain, all the others were dissolved.…”

“…Precipitate microstructure was examined in the past in IN738LC alloy both ex situ and in situ at elevated temperatures [4] using Small-Angle Neutron Scattering (SANS) technique [5]. It was found that additional precipitates in the channels between the large primary ones are formed either during slow cooling from high temperature or after reheating above 570˝C [4].…”

“…It was found that additional precipitates in the channels between the large primary ones are formed either during slow cooling from high temperature or after reheating above 570˝C [4]. The new precipitates presumably affect mechanical properties as such small (tertiary) precipitates very significantly contribute to strengthening in polycrystalline superalloys [6,7].…”