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Metallurgical and Materials Transactions A

, Volume 38, Issue 4, pp 883–893 | Cite as

Eta Phase and Boride Formation in Directionally Solidified Ni-Base Superalloy IN792 + Hf

  • S.M. SeoEmail author
  • I.S. Kim
  • J.H. Lee
  • C.Y. Jo
  • H. Miyahara
  • K. Ogi
Article

Abstract

A series of directional solidification experiments have been conducted to elucidate the formation mechanism of eta and Cr-rich phases in the Ni-base superalloy IN792 + Hf. Both eta and Cr-rich phases were found to be the final solidification products developed from the remaining liquid after γ/γ′ eutectic reaction. The (Ti + Ta + Hf)/Al ratio in the residual liquid played a significant role in the nucleation of eta phase. During the solidification of γ/γ′ eutectic, the continual increase of (Ti + Ta + Hf)/Al ratio in the residual liquid eventually led to the completion of γ/γ′ eutectic reaction and caused the nucleation of eta phase. The results of electron probe microanalysis and transmission electron microscopy revealed that the Cr-rich phase was Cr, Mo, and W containing M5B3 and M3B2 type borides. The formation of these boride phases was found to be strongly influenced by the formation of γ/γ′ eutectic. Because of the limited solubility of Cr, Mo, and W in γ′ phase, these elements were enriched in the residual liquid during the solidification of γ/γ′ eutectic. In addition, boron would preferentially segregate into liquid due to its very limited solubility in both γ and γ′ phases so that the possibility of boride formation in the residual liquid ahead of the γ/γ′ eutectic was increased. A modified Scheil model was adopted to explain the influence of solidification rate on the formation of eta phase and borides, and the results were discussed.

Keywords

Eutectic Reaction Residual Liquid Directionally Solidify Dendrite Core Boride Phase 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

This work was supported by the National Research Laboratory Project of the Korean Ministry of Science and Technology. The authors also acknowledge the support of the Japan Society for the Promotion of Science through the RONPAKU Fellowship.

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Copyright information

© THE MINERALS, METALS & MATERIALS SOCIETY and ASM INTERNATIONAL 2007

Authors and Affiliations

  • S.M. Seo
    • 1
    Email author
  • I.S. Kim
    • 1
  • J.H. Lee
    • 2
  • C.Y. Jo
    • 1
  • H. Miyahara
    • 3
  • K. Ogi
    • 4
  1. 1.ECO-Materials Research CenterKorea Institute of Machinery & MaterialsChangwonKorea
  2. 2.Department of Metallurgy and Materials EngineeringChangwon UniversityChangwonKorea
  3. 3.Department of Materials Science and EngineeringKyushu UniversityFukuokaJapan
  4. 4.Oita National College of TechnologyOitaJapan

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