Ausscheidungsverhalten der Ni-Basis-Superlegierung 718

Translated title of the contribution: Precipitation behaviour of the Ni-base-superalloy 718

Christoph Turk

Research output: ThesisDiploma Thesis

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Abstract

Ni-base superalloys within all high-temperature materials are the most mechanical, thermal and corrosion resistent materials. Hence these alloys are widely used as forging and casting products in the high temperature technology. The strength of Ni-base superalloys results from the particle strengthening of intermetallic precipitates within a face centered cubic Ni-matrix. The aim of this work was the atom probe tomography (APT) characterization of the precipitation behaviour of the Ni-base superalloy 718 and of a model-alloy with a similar chemical composition to superalloy 718. It is well known that in both alloys the two-step aging treatment causes a precipitation of spherical γ’ (Ni3Al)- and disc-shaped γ’’ (Ni3Nb)-precipitates. For this reason the precipitation reaction has been investigated at defined heat treatments within the two-step aging and at fully heat-treated samples. Due to the atom probe tomography it was possible to gain information on the chemical composition, the volume fraction, the average size, the average distance and the morphology of both types of precipitates. Special interest was focused on the precipitate evolution of the γ’- and γ’’ -dual phase nature in those alloys, which already occurred in the early stages of precipitation. The analysis of the aging kinetics showed that both phases transformed from spherical to disc-shaped particles. In addition to this the effect of a lower and a higher solution annealing temperature on the precipitation behaviour has been studied. Subsequently the investigations of the fully heat-treated specimen showed no evidence that smaller precipitates were generated by the cooling sequence after the second stage of aging.
Translated title of the contributionPrecipitation behaviour of the Ni-base-superalloy 718
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Leitner, Harald, Supervisor (internal)
  • Siller, Ingo, Supervisor (external), External person
  • Clemens, Helmut, Co-Supervisor (internal)
Award date29 Jun 2012
Publication statusPublished - 2012

Bibliographical note

embargoed until 26-06-2017

Keywords

  • Ni-base superalloy
  • Inconel 718
  • Atom probe tomography
  • precipitates
  • Ni3Al
  • Ni3Nb
  • Early stages of precipitation
  • dual phase nature

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