Variations in microstructure and properties of GH783 alloy after long term thermal exposure

Investigation was made on changes in microstructure, mechanical properties and coefficient of thermal expansion for low coefficient of thermal expansion superalloy GH783 after long term aging at 650, 700 and 750 degrees C. Scanning electron microscopy examination revealed that aging at 650 degrees C for 3000 h did not cause significant change in the characteristics of gamma' precipitates, but alloy strength at room temperature and at 650 degrees C, as well as stress rupture life at 650 degrees C were all slightly increased. Aging at 700 degrees C for 1000 h lead to a slight reduction in strength of the alloy at room temperature and at 650 degrees C because of coarsening of the gamma' precipitates, but the stress rupture life at 650 degrees C was not significantly reduced. Aging at 750 degrees C for 1000 h caused large reduction in strength and sharp reduction in stress rupture life at 650 degrees C because of excessive coarsening of the gamma' precipitates and an increase in the amount of beta-NiAl phase. Nb-enriched Laves phase was also found precipitating within the beta-NiAl phase after long term thermal exposure, but no evident influence was found on the mechanical properties of the alloy. (c) 2006 Elsevier B.V. All rights reserved.