Constrained cavity growth models of longitudinal creep deformation of oxide dispersion strengthened alloys |
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Authors: | Stephens J J Nix W D |
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Affiliation: | (1) Division 1832, Sandia National Laboratories, P.O. Box 5800, 87185 Albuquerque, NM;(2) Department of Materials Science and Engineering, Stanford University, Building 550, 94305 Stanford, CA |
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Abstract: | Two models of constrained cavity growth are developed to describe the long-term longitudinal creep behavior of nickel based
oxide dispersion strengthened (ODS) alloys. For both models the rupture time is taken as the time for a transverse grain boundary
to cavitate fully. A diffusive cavity growth law is assumed to govern cavitation. The applicability of the respective models
is determined by the particular grain morphology achieved by thermal-mechanical processing. The first model assumes that longitudinal
grain boundaries are unable to slide; hence displacements due to cavitation must be matched by displacements due to dislocation
creep in adjoining grains. This model predicts a low stress exponent at the transition from single crystal to cavitation creep
behavior, and higher stress exponents at stresses below this transition. Good agreement is found between the model predictions
and creep data for MA 754 at 1000 and 1093 °C. A second model considers a grain morphology wherein longitudinal grain boundaries
are able to slide by means of deformation of pockets of fine grains. Cavitation of transverse grain boundaries is thus controlled
by grain boundary sliding. This model predicts a stress exponent of 1 at low stresses, and serves as an upper bound for the
creep rate when a duplex grain morphology is present. Model predictions are in good agreement with creep data for a heat of
MA 754 with a duplex grain morphology.
Formerly Graduate Research Assistant in the Department of Materials Science and Engineering at Stanford University |
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