Abstract
Inconel 718 is a nickel-iron based superalloy widely used in the aerospace industry. Its high temperature strength is attributed to the thermal stability of dense nanoscale precipitates and . There is experimental evidence that and often form co-precipitates or sandwichlike structure or . But how they stabilize under heat treatment or in service is still not well-understood. We have investigated the interfacial structure and chemistry of fine co-precipitates in Inconel 718, using both first-principles density functional theory calculation and the three-dimensional atom probe technique. Our calculations confirm that Al atoms in the phase segregate to the interface. The enrichment of Al helps to impede the assimilation of Nb from to and reject Al from to , and therefore keeps such secondary precipitates at fine size. In the absence of Ti in the phase, our calculations predict an enhanced driving force for Al to accumulate at the interface. We have also characterized the microstructure of the interface for an Inconel 718 sample taken from a commercial compressor blade serviced in an airplane engine for over at a temperature up to using three-dimensional atom probe analysis. Interestingly, we find that Al enrichment sustains long-term service, suggesting that the coarsening of secondary precipitates is interface-controlled. The success of first-principles density functional theory computation in reproducing the experimental observation encourages extensive application of this powerful tool in the study of precipitates in superalloys.
4 More- Received 9 August 2007
DOI:https://doi.org/10.1103/PhysRevB.76.224102
©2007 American Physical Society