Lattice strain evolution and load partitioning during creep of a Ni-based superalloy single crystal with rafted γ′ microstructure

James Coakley*, Dong Ma, Matthew Frost, David Dye, David N. Seidman, David C. Dunand, Howard J. Stone

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

In-situ neutron diffraction measurements were performed on monocrystalline samples of the Ni-based superalloy CMSX-4 during N-type γ′ raft formation under the tensile creep conditions of 1150 °C/100 MPa, and subsequently on a rafted sample under the low temperature/high stress creep conditions of 715 °C/825 MPa. During 1150 °C/100 MPa creep, the γ′ volume fraction decreased from ∼70% to ∼50%, the lattice parameter misfit was partly relieved, and the load was transferred from the creeping γ matrix to the γ′ precipitates. On cooling back to room temperature, a fine distribution of γ′ precipitates formed in the γ channels, and these precipitates were present in the 715 °C/825 MPa creep regime. Under low temperature/high stress creep, the alloy with rafted γ′ microstructure exhibited superior creep strength to the cuboidal γ′ microstructure produced following a standard heat-treatment. A lengthy creep incubation period was observed, believed to be associated with {111}〈110〉 dislocations hindering propagation of {111}〈112〉 dislocations. Following the creep incubation period, extensive macroscopic creep strain accumulated during primary creep as the γ phase yielded. Finally, the diffraction data suggest a loss of precipitate/matrix coherency in the (0k0) interfaces as creep strain accumulated.

Original languageEnglish (US)
Pages (from-to)77-87
Number of pages11
JournalActa Materialia
Volume135
DOIs
StatePublished - Aug 15 2017

Keywords

  • Creep
  • Directional coarsening
  • Neutron diffraction
  • Precipitation
  • Superalloys

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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