Characterization of abnormal grain coarsening in Alloy 718

Richard Watson, Michael Preuss, João Quinta Da Fonseca, Thomas Witulski, Gregor Terlinde, Markus Büscher

Research output: Chapter in Book/Report/Conference proceedingConference PaperOther

6 Citations (Scopus)


Even though the phenomenon of abnormal grain coarsening (AGC) or "exploded grains" has been known to occur in Alloy 718 industrial forgings there is still no satisfactory explanation for it. For this reason, detailed microstructure analysis has been carried out in normal and abnormal regions. Electron Backscatter Diffraction (EBSD) was employed to determine grain size, boundary distribution and measure stored energy, while backscattered imagining in a FEGSEM was used to measure δ precipitate size and morphology. It was found that abnormal regions show almost 3 times as many twin boundaries compared to a normal region. In addition, the δ phase morphologies differ very significantly when comparing these two different regions. Normal regions display δ phase with a plate like nature, whereas in abnormal regions, δ particles appear to be more spherical. Furthermore, there are clear indications of differences in δ volume fractions between the two regions. Whilst in normal regions the δ phase is found predominantly at grain boundaries, in abnormal regions the δ is also found within grains. Both backscatter images and EBSD scans indicate that there are higher levels of stored energy within the normal regions, compared to the abnormal regions. These observations suggest that AGC occurs in regions where dynamic recrystallization does not happen and where recrystallization during solution heat treatment is affected by the local particle distribution.

Original languageEnglish
Title of host publicationEUROSUPERALLOYS 2014
Subtitle of host publication2nd European Symposium on Superalloys and their Applications
Number of pages5
Publication statusPublished - 2014
Externally publishedYes
EventEuropean Symposium on Superalloys and Their Applications 2014 - Giens, France
Duration: 12 May 201416 May 2014
Conference number: 2nd

Publication series

NameMATEC Web of Conferences
PublisherEDP Sciences
ISSN (Print)2261-236X


ConferenceEuropean Symposium on Superalloys and Their Applications 2014
Abbreviated titleEUROSUPERALLOYS 2014
Internet address

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