Frank loop unfaulting mechanism in fcc metals during neutron irradiation Page: 4 of 13
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HEDL-SA-2078
A FRANK LOOP UNFAULTING MECHANISM IN
fee METALS DURING NEUTRON IRRADIATION
D. S. Gel 1es
ABSTRACT
The unfaulting mechanism whereby sessile Frank dislocation loops evolve
into a complex tangle of glissile dislocations during irradiation of face
centered cubic metals is not well understood. It is generally presumed that
such loops grow by absorption of point defects until interactions develop
which provide sufficient impetus for nucleation of an unfaulting event. The
loops then become glissile, interact and form a dislocation network.
The present study identifies an alternate mechanism which has been ob-
served to occur in an austenitic precipitation-strengthened commercial alloy
irradiated in the EBR-II fast reactor. The mechanism requires an inter-
action between the sessile |<111> Frank loop and a moving glissile |<TT0>
perfect dislocation. An unfauTting |<112> dislocation is created which, as
it moves, eliminates the Frank loop and leaves only a perfect dislocation
with the original |<110> Burgers vector. This process is demonstrated by
an example illustrated with transmission electron micrographs.
This alternate mechanism can have significant impact on the development
of the dislocation microstructure in a metal undergoing irradiation creep.
This impact will be discussed in relation to relevant irradiation creep
models.
INTRODUCTION
Irradiation creep is an important behavioral response which must be
considered in the development of structural materials for fast breeder
reactors. Irradiation creep occurs as a result of enhanced concentrations
of point defects produced by bombardment with highly energetic neutrons.
Increases in point defect concentrations lead to increased dislocation
climb rates which in turn generally result in enhanced creep rales. Two
approaches can be taken to quantify irradiation creep response. Creep tests
can be performed in-reactor to obtain data for specific alloy conditions
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Gelles, D. S. Frank loop unfaulting mechanism in fcc metals during neutron irradiation, article, May 1980; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc1065818/m1/4/: accessed August 15, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.