Untersuchung des meta-dynamischen Rekristallisationsverhaltens der Nickelbasislegierung Allvac 718PlusTM und Optimierung der numerischen Gefügesimulation in Deform 2DTM

Translated title of the contribution: Meta-dynamic recrystallization of the nickel-based alloy Allvac 718PlusTM - Investigation and microstructure simulation in Deform 2DTM

Daniel Huber

Research output: ThesisDiploma Thesis

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Abstract

Aerospace gas turbine disks operate in an environment of high stresses caused by centrifugal forces and elevated temperatures. These severe conditions necessitate the need for materials with high temperature strength and good low cycle fatigue resistance. One class of alloys used for this task are nickel based superalloys, out of which, the new grade Allvac 718PlusTM shall further enhance the high temperature properties. The mechanical properties of Allvac 718PlusTM are sensitive to the microstructure, in particular to the grain size, which depends on the processing history. The final grain structure is mainly influenced by thermo-physical processes like recrystallization and grain growth, as well as by the precipitation kinetics. In former works the kinetics of dynamic and static recrystallization, as well as grain growth was investigated. The objective of this work was the determination of the kinetics of meta-dynamic recrystallization. Therefore double-hit compression tests in a temperature range of 950-1050 °C were performed and the flow stress curves were analyzed by use of a newly developed method. Based on knowledge of prior tests the temperature range was divided into two parts. These two ranges were both above and below the solvus temperatur of the delta-phase. Differences in the recrystallization kinetics in each temperature range were observed, based on the pinning of the grain boundaries by the delta-phase. The recrystallized fraction was calculated using the methods mentioned above and validated by optical microscopy. By use of these data the kinetics of meta-dynamic recrystallization was determined based on the Johnson-Mehl-Avrami-Kolmogorov-equation. The resulting parameters were furthermore implemented into the Finite Element code Deform 2DTM, allowing the prediction of the microstructure due to meta-dynamic recrystallization, which is a function of locally varying process parameters, i.e. temperature and strain rate, during hot closed die forging.
Translated title of the contributionMeta-dynamic recrystallization of the nickel-based alloy Allvac 718PlusTM - Investigation and microstructure simulation in Deform 2DTM
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Sommitsch, Christof, Supervisor (internal)
Award date26 Jun 2009
Publication statusPublished - 2009

Bibliographical note

embargoed until null

Keywords

  • nickel-based alloy recrystallization closed die forging modelling modeling simulation

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