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Microstructural and Mechanical Characterization of Directionally Solidified Conventional and Nb-Modified Mar-M247 Superalloy

  • A. M. S. CostaEmail author
  • E. S. N. Lopes
  • R. J. Contieri
  • R. Caram
  • R. Baldan
  • G. E. Fuchs
  • C. A. Nunes
Article
  • 19 Downloads

Abstract

This study analyzes the effects of replacing Ta by Nb (at.% basis) in the phase transformation temperatures, Scheil solidification behavior, and microstructural mechanical features of a Nb-modified as well as conventional Mar-M247 superalloys. Both alloys were directionally solidified at a withdrawal rate of 18 cm/h under a thermal gradient of about 80 °C/cm. DSC results were compared to thermodynamic simulations of phase transformation temperatures and showed a good correlation. The replacement of Ta by Nb has not altered the solidification path of Mar-M247, keeping the sequence L → L + γ → L + γ + MC → L + γ + MC + γ/γ′ eutectic. Due to the segregation of Hf and Zr to the very last liquid to solidify, a low melting point γ/Ni5(Hf,Zr) constituent was observed. The as-solidified microstructures of both Mar-M247(Nb) and Mar-M247 were constituted of columnar dendrites of gamma matrix (γ) phase with cuboidal gamma-prime (γ′) precipitates. In addition, γ/γ′-eutectic was observed in the interdendritic region along with MC carbides in blocky, script (blocky dendritic), needle-like and fine nodular morphologies. Both alloys contained about 1.5 vol.% of MC carbides. The MC carbides in Mar-M247(Nb) and Mar-M247 are, respectively, Nb-rich and Ta-rich, with only a limited amount of Hf being detected in the MC phase. The yield stress of Nb-modified Mar-M247 showed higher values up to 750 °C. For higher temperatures, above 800 °C, a conventional Mar-M247 presented a higher value of yield stress.

Keywords

Mar-M247 superalloy Nb-modified Mar-M247 thermodynamic simulation 

Notes

Acknowledgments

The authors acknowledge CAPES (Brasília, Brazil) for funding and supporting this project (Program RIPS/Pró-Engenharias).

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Copyright information

© ASM International 2019

Authors and Affiliations

  • A. M. S. Costa
    • 1
    Email author
  • E. S. N. Lopes
    • 2
  • R. J. Contieri
    • 3
  • R. Caram
    • 2
  • R. Baldan
    • 4
  • G. E. Fuchs
    • 5
  • C. A. Nunes
    • 6
  1. 1.Methodist University of PiracicabaSanta Bárbara d’OesteBrazil
  2. 2.School of Mechanical EngineeringUniversity of CampinasCampinasBrazil
  3. 3.School of Applied SciencesUniversity of CampinasLimeiraBrazil
  4. 4.São Paulo State University (Unesp)ItapevaBrazil
  5. 5.Materials Science and Engineering DepartmentUniversity of FloridaGainesvilleUSA
  6. 6.Escola de Engenharia de LorenaUniversidade de Sao PauloLorenaBrazil

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