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Evolution of γ′ Precipitation Kinetics and Morphology in a Ni- 13.36 at.% Al Alloy Aged Under Compression

Published online by Cambridge University Press:  10 February 2011

S. V. Prikhodko ,
R. T. Nielsen  and
A. J. Ardell
S. V. Prikhodko
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, [email protected]
R. T. Nielsen
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, [email protected]
A. J. Ardell
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, [email protected]
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Abstract

The influence of an applied uniaxial compressive stress on the coarsening of γ′ (Ni3A1) precipitates at 640°C in a Ni-13.36 at. % Al alloy was studied experimentally. The investigation was done using cylindrical doubly-tapered monocrystalline specimens with axes of revolution parallel to [100]. At an applied load of 940 N the compressive stress varied from ∼30 to ∼130 MPa in any given specimen. Over this range of stresses the strain was primarily elastic. Dark-field transmission electron microscopy, coupled with image-analysis software, was used to characterize evolution of the γ′ precipitate morphology, and the kinetics of coarsening in (100) were investigated for aging times up to 504 h. We find, quite unexpectedly, that the relationship between the kinetics of coarsening and the applied stress is not monotonic. Instead, a maximum in the coarsening rate obtains at an intermediate stress, in the neighborhood of 55 ± 10 MPa. Theoretical work by Johnson predicts that for certain combinations of lattice and elastic-constant mismatch, an extremum of the solubility limit exists in elastically isotropic specimens aged under uniaxial stress. The theory is not sophisticated enough to enable a quantitative comparison with experimental results, but provides some rationale for our unexpected finding.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 481: Symposium P – Science and Technology of Semiconductor Surface Preparation , 1997 , 169
Copyright
Copyright © Materials Research Society 1998

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