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Influence of Heat Treatment on Size and Morphology of Various γ′ Phase in IN738LC and GTD-111 Superalloys

Mardiha, Pourya | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50870 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Asgari, Sirous
  7. Abstract:
  8. Gamma prime (γ') precipitates are the most important phase in nickel-base superalloys that rise to a combination of desirable properties in superalloys. The morphology of these particles has important contribution to the resulting properties of superalloys. Heat treatment process of superalloys is one of the most important factors affecting the characteristics of the γ' phase. In this study, nickel-base superalloys IN738LC and GTD-111 were used to study the evolution of the microstructure and morphology of the γ' precipitates under a variety of heat treatment cycles including partial dissolution, aging for different times and under a range of cooling rates. Morphology and characteristics of precipitates were studied by SEM and optical microscopy. The results of this study, showed various morphologies of the γ' precipitates under different heat treatment cycles. These morphologies were justified using Gibbs-Thomson theory, role of elastic strains arising from precipitate-matrix mismatch, heterogeneity of chemical composition and occurrence of antiphase boundaries. One of the most common morphologies observed was multiple aggregates of γ' precipitates that in most cases started from the mid surfaces. The onset of splitting of the primary cubic precipitates was addressed based on the above mentioned mechanisms. After the aging heat treatment, one of the important results was observation of a regular arrangement of secondary cubic precipitates. This regular arrangement was justified based on the decrease of elastic strain in the alloy. Using the data obtained in this study, a mechanism for the formation of regular arrangement of secondary precipitates was proposed
  9. Keywords:
  10. Superalloys ; Heat Treatment ; Size Effect ; Morphological Operation ; Morphology ; Inconel 738 Superalloy ; GTD-111 Superalloy ; Precipitate Splitting

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