Microstructure controlling of U720-typed superalloys to improve a hot and cold workability by using incoherent gamma prime

A. Ota, N. Ueshima, K. Oikawa, S. Imano

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

1 Citation (Scopus)

Abstract

For high performance air craft engine disks, high-performance Ni-based wrought superalloys (e.g. U720Li™, AD730™) with over 40vol% of the γ' phase at 600-700 °C have been developed. Applying them to gas turbines is expected to improve the efficiency. However, due to their low workability, it is difficult to make large size components. We have developed a new innovadve process (the MH process) to improve the workability of high-performance Ni-based wrought superalloys. The strengthening mechanism of these γ' precipitation-typed superalloys is widely known to be enhanced by the coherent interface between the y phase and γ' phase. We focused on the incoherent γʹ phase that precipitated on the y phase grain boundary during forging and it was found that the incoherent boundary shows no strengthening effect. Formation of y/incoherent y' two-phase microstructure would dramatically improve their workability. Cold working was achieved by applying the MH process to the U720-type alloy AD730. The MH process made it possible to fabricate cold rolled sheets, cold drawn wires and the forged turbine blades. It also exhibited excellent ductility at high temperature; we obtained 99% reduction of area at over 920 °C and 500% elongation at 950 °C by applying the MH process. It was demonstrated that U720Li can be processed by die forging at low temperature and high strain rate without using superplastic forming. In this study, we investigated how the heat treatment condition affects the formation of unique microstructures with good hot and cold workability.

Original languageEnglish
Title of host publicationProceedings of the 9th International Symposium on Superalloy 718 and Derivatives
Subtitle of host publicationEnergy, Aerospace, and Industrial Applications
EditorsKarl Heck, Kevin Bockenstedt, Jon Groh, Daisuke Nagahama, Paul Jablonski, Zhongnan Bi, Chantal Sudbrack, Ian Dempster, Max Kaplan, Eric Ott, Xingbo Liu, Joel Andersson
PublisherSpringer International Publishing
Pages987-999
Number of pages13
ISBN (Electronic)9783319894799
DOIs
Publication statusPublished - 2018 Jan 1
Event9th International Symposium on Superalloy 718 and Derivatives: Energy, Aerospace, and Industrial Applications - Pittsburgh, United States
Duration: 2018 Jun 32018 Jun 6

Publication series

NameMinerals, Metals and Materials Series
Volume2018-June
ISSN (Print)2367-1181
ISSN (Electronic)2367-1696

Conference

Conference9th International Symposium on Superalloy 718 and Derivatives: Energy, Aerospace, and Industrial Applications
CountryUnited States
CityPittsburgh
Period18/6/318/6/6

Keywords

  • Forging
  • Superalloys
  • Workability
  • γ'

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy Engineering and Power Technology
  • Mechanics of Materials
  • Metals and Alloys
  • Materials Chemistry

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