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Creep behavior of a γ′-strengthened Co-base alloy with zero γ/γ′-lattice misfit at 800 °C, 196 MPa

Published online by Cambridge University Press:  09 November 2017

Jan Midtlyng ,
Alexander I. Epishin ,
Nikolay V. Petrushin ,
Thomas Link ,
Gert Nolze ,
Igor L. Svetlov  and
Walter Reimers
Jan Midtlyng
Affiliation:
Institute of Materials Science and Technologies, Technical University of Berlin, Berlin 10587, Germany
Alexander I. Epishin*
Affiliation:
Institute of Materials Science and Technologies, Technical University of Berlin, Berlin 10587, Germany
Nikolay V. Petrushin
Affiliation:
All-Russian Scientific Research Institute of Aviation Materials (VIAM), Department of Superalloys, Moscow 105005, Russia
Thomas Link
Affiliation:
Institute of Materials Science and Technologies, Technical University of Berlin, Berlin 10587, Germany
Gert Nolze
Affiliation:
Federal Institute for Materials Research and Testing (BAM), Department of Materials Engineering, Berlin 12205, Germany
Igor L. Svetlov
Affiliation:
All-Russian Scientific Research Institute of Aviation Materials (VIAM), Department of Superalloys, Moscow 105005, Russia
Walter Reimers
Affiliation:
Institute of Materials Science and Technologies, Technical University of Berlin, Berlin 10587, Germany
*
a)Address all correspondence to this author. e-mail: a.epishin@tu-berlin.de
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Abstract

Deformation and structural behavior of an experimental γ′-strengthened Co-base alloy during creep at 800 °C and 196 MPa have been investigated. The characteristic features of this alloy are zero γ/γ′-lattice misfit and a fine γ/γ′-microstructure. In the initial condition, the γ′-precipitates in this alloy are small (size of about 100 nm), have polyhedral morphology, and are separated by the very narrow γ-channels (width of about 10 nm). The tests performed up to about 1% creep strain (about 500 h creep time) gave creep curves with a slow constant strain rate and without an apparent transient creep, typical for superalloys with nonzero misfit. In this initial stage of creep, entering of the narrow γ-channels by dislocations is blocked by a strong Orowan force. The micromechanism of creep was identified as an octahedral glide of 〈011〉 superdislocations simultaneously in two phases, γ and γ′. The γ/γ′-microstructure with zero misfit shows no rafting but rapidly coarsens isotropically. It is concluded that zero misfit is beneficial at the initial stages of the creep but is unfavourable for long-term creep because of the continuous microstructural coarsening.

Keywords

alloymicrostructuredislocations
Type
Articles
Information
Journal of Materials Research , Volume 32 , Issue 24: Focus Issue: Mechanical Properties and Microstructure of Advanced Metallic Alloys—in Honor of Prof. Haël Mughrabi PART B , 28 December 2017 , pp. 4466 - 4474
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Copyright © Materials Research Society 2017 

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Footnotes

Contributing Editor: Gunther Eggeler

References

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