On the grain boundary strengthening effect of boron in γ/γ′ Cobalt-base superalloys

Journal article
(Original article)


Publication Details

Author(s): Kolb M, Freund L, Fischer F, Povstugar I, Makineni SK, Gault B, Raabe D, Müller J, Spiecker E, Neumeier S, Göken M
Journal: Acta Materialia
Publication year: 2018
Pages range: 247-254
ISSN: 1359-6454
Language: English


Abstract



Boron is an essential solute element for improving the grain boundary strength in several high temperature metallic alloys especially in Ni- and Co-base superalloys although the detailed strengthening mechanisms are still not well understood. In superalloys, boron leads to the formation of borides and precipitate depleted zones around the grain boundaries and alters the bond strength among the grains directly. In this paper, we explore in detail the role of the boron content in ternary γ/γ′ Co-9Al-9W alloys. Local as well as bulk mechanical properties were evaluated using nanoindentation and compression testing and correlated to near-atomic scale microstructure and compositions obtained from electron microscopy and atom probe tomography.



The alloy variant with low B content (0.005 at.% B) reveals an increase in yield strength at room temperature and 600 °C and atom probe tomography investigations show that solute B segregates to the grain boundaries. However, in the bulk B exclusively partitions to the γ′ phase. Additionally, the γ′/γ′ grain boundaries are depleted in W and Al with the concentration locally shifted towards the γ composition forming a very thin γ layer at the γ′/γ′ grain boundaries, which supports dislocation mobility in the γ′/γ′ grain boundary region during deformation. Higher content of B (0.04 at.% B) promotes formation of W-rich borides at the grain boundaries that leads to undesirable precipitate depleted zones adjacent to these borides that decrease the strength of the alloy drastically. However, it was also found that a subsequent annealing heat treatment eliminates these detrimental zones by re-precipitating γ′ and thus elevating the strength of the alloy.



This result shows that, if a precipitate depleted zone can be avoided, B significantly improves the mechanical properties of polycrystalline Co-base superalloys by strengthening the γ′ phase and by improving grain boundary cohesion.




 


FAU Authors / FAU Editors

Fischer, Florian
Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)
Freund, Lisa
Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)
Göken, Mathias Prof. Dr.
Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)
Kolb, Markus
Sonderforschungsbereich/Transregio 103 Vom Atom zur Turbinenschaufel - wissenschaftliche Grundlagen für eine neue Generation einkristalliner Superlegierungen
Müller, Julian Dr.-Ing.
Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung)
Neumeier, Steffen Dr.-Ing.
Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)
Spiecker, Erdmann Prof. Dr.
Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung)


Additional Organisation
Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung)
Interdisziplinäres Zentrum, Center for Nanoanalysis and Electron Microscopy (CENEM)


External institutions with authors

Max-Planck-Institut für Eisenforschung GmbH (MPIE) / Max Planck Institute for Iron Research


How to cite

APA:
Kolb, M., Freund, L., Fischer, F., Povstugar, I., Makineni, S.K., Gault, B.,... Göken, M. (2018). On the grain boundary strengthening effect of boron in γ/γ′ Cobalt-base superalloys. Acta Materialia, 247-254. https://dx.doi.org/10.1016/j.actamat.2017.12.020

MLA:
Kolb, Markus, et al. "On the grain boundary strengthening effect of boron in γ/γ′ Cobalt-base superalloys." Acta Materialia (2018): 247-254.

BibTeX: 

Last updated on 2019-27-05 at 17:08