Dislocation decorrelation and relationship to deformation microtwins during creep of a γ′ precipitate strengthened Ni-based superalloy

R. R. Unocic, N. Zhou, L. Kovarik, C. Shen, Y. Wang, M. J. Mills

Research output: Contribution to journalArticlepeer-review

163 Scopus citations

Abstract

The evolution of microtwins during high temperature creep deformation in a γ′ strengthened Ni-based superalloy has been investigated through a combination of creep testing, transmission electron microscopy (TEM), theoretical modeling, and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of creep deformation. Deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a/2〈1 1 0〉 matrix-type dislocations. Due to fine channels between the γ′ particles, coupled with a low γ matrix stacking fault energy, the a/2〈1 1 0〉 matrix dislocations dissociate into a/6〈1 1 2〉 Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the γ matrix. Microtwins are common and form via Shockley partial dislocations, cooperatively shearing both the γ and γ′ phases on adjacent {1 1 1} glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. The important processes of dislocation dissociation and decorrelation were modeled in detail through phase field simulations and theoretical analyses based on Orowan looping, providing a comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in γ′ strengthened Ni-based superalloys.

Original languageEnglish
Pages (from-to)7325-7339
Number of pages15
JournalActa Materialia
Volume59
Issue number19
DOIs
StatePublished - Nov 2011

Funding

Acknowledgement is given to support from the US Air Force sponsored Metals Affordability Initiative (MAI) project entitled “Durable high temperature disk material”. Team members include Pratt & Whitney, GE Aviation, Georgia Institute of Technology, The Ohio State University, and the University of Rhode Island. The authors would like to thank the Air Force Office of Scientific Research for their support under the AFOSR MEANS II program. R.R.U. would like to acknowledge support from the Alvin M. Weinberg Fellowship of Oak Ridge National Laboratory, managed by UT-Battelle for the US Department of Energy.

Keywords

  • Atomic ordering
  • Creep
  • Diffusion
  • Microtwinning
  • Shockley partial dislocations

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