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Observation of a New Creep Regime in Polycrystatiitne Ni-50(at.%)Al Intermetallic Alloy

Published online by Cambridge University Press:  01 January 1992

S. V. Raj  and
Serene C. Farmer
S. V. Raj
Affiliation:
NASA Lewis Research Center, MS 49-1, Cleveland, OH 44135.
Serene C. Farmer
Affiliation:
NASA Lewis Research Center, MS 49-1, Cleveland, OH 44135.
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Abstract

Constant load creep tests were conducted on fine-grained ( - 23 µm) polycrystalline Ni-50(at.%) Al in the temperature range 1000 - 1400 K. Power-law creep with an average stress exponent, n, of 6.6 and an average activation energy, Qc, of about 300 kJ mol-1 was observed above 25 MPa, while n ≈ 2 and Qc ≈ 95 kJ mol-1 for σ < 25 MPa. Primary creep was observed in both regions thereby signifying dislocation activity during the initial period of the test. Preliminary experiments with coarse-grained Ni-50A1 suggested that the rtechanism in the n = 2 region is dependent on grain size. Transmission electron microscopy observations of the deformed specimens revealed dislocation tangles, dipoles, loops and networks in the power-law creep regime. The Burgers vector was determined to be <100> with the dislocations lying on the {100} and {110} planes. Although well-defined subgrains were not always observed, there was a greater tendency towards subgrain formation at stresses above 25 MPa. The deformation microstructures were inhomogeneous in the n = 2 creep regime and many grains did not reveal any dislocation activity. The observed characteristics of the low stress region suggest the dominance of an acccanmodated grain boundary sliding mechanism.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 288: Symposium L – High-Temperature Ordered Intermetallic Alloys V , 1992 , 647
Copyright
Copyright © Materials Research Society 1995

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References

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