Compositional variations for small-scale gamma prime (γ′) precipitates formed at different cooling rates in an advanced Ni-based superalloy

Y. Q. Chen, E. Francis, J. Robson, M. Preuss, S. J. Haigh

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Abstract

Size-dependent compositional variations under different cooling regimes have been investigated for ordered L12-structured gamma prime (γ′) precipitates in the commercial powder metallurgy Ni-based superalloy RR1000. Using scanning transmission electron microscope imaging combined with absorption-corrected energy-dispersive X-ray spectroscopy, we have discovered large differences in the Al, Ti and Co compositions for γ′ precipitates in the size range 10-300 nm. Our experimental results, coupled with complementary thermodynamic calculations, demonstrate the importance of kinetic factors on precipitate composition in Ni-based superalloys. In particular, these results provide new evidence for the role of elemental diffusion kinetics and aluminium antisite atoms on the low-temperature growth kinetics of fine-scale γ′ precipitates. Our findings have important implications for understanding the microstructure and precipitation behaviour of Ni-based superalloys, suggesting a transition in the mechanism of vacancy-mediated diffusion of Al from intrasublattice exchange at high temperatures to intersublattice antisite-assisted exchange at low temperatures.

Original languageEnglish
Pages (from-to)199-206
Number of pages8
JournalActa Materialia
Volume85
DOIs
Publication statusPublished - 15 Feb 2015
Externally publishedYes

Keywords

  • Cooling rate
  • Energy-dispersive
  • Ni-based superalloys
  • Scanning transmission electron microscopy
  • X-ray spectroscopy

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