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Title: Investigation of strain aging in the ordered intermetallic compound beta-NiAl. Ph.D. Thesis final contractor report

Abstract

The phenomenon of strain aging has been investigated in polycrystalline and single crystal NiAl alloys at temperatures between 300 and 1200 K. Static strain aging studies revealed that after annealing at 1100 K for 7200 s (i.e., 2h) followed by furnace cooling, high purity, nitrogen-doped and titanium-doped polycrystalline alloys exhibited continuous yielding, while conventional-purity and carbon-doped alloys exhibited distinct yield points and Luders strains. Prestraining by hydrostatic pressurization removed the yield points, but they could be reintroduced by further annealing treatments. Yield points could be reintroduced more rapidly if the specimens were prestrained uniaxially rather than hydrostatically, owing to the arrangement of dislocations into cell structures during uniaxial deformation. The time dependence of the strain aging events followed a t(exp 2/3) relationship suggesting that the yield points observed in polycrystalline NiAl were the result of the pinning of mobile dislocations by interstitials, specifically carbon. Between 700 and 800 K, yield stress plateaus, yield stress transients upon a ten-fold increase in strain rate, work hardening peaks, and dips in the strain rate sensitivity (SRS) have been observed in conventional-purity and carbon-doped polycrystals. In single crystals, similar behavior was observed; in conventional-purity single crystals, however, the strain rate sensitivity became negative resultingmore » in serrated yielding, whereas, the strain rate sensitivity stayed positive in high purity and in molybdenum-doped NiAl. These observations are indicative of dynamic strain aging (DSA) and are discussed in terms of conventional strain aging theories. The impact of these phenomena on the composition-structure-property relations are discerned.« less

Authors:
Publication Date:
Research Org.:
Florida Univ., Gainesville, FL (United States)
OSTI Identifier:
161013
Report Number(s):
N-96-12501; NASA-CR-198364; E-9771; NAS-1.26:198364
CNN: NGT-2958;RTOP 505-63-52; TRN: 9612501
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: TH: Ph.D. Thesis Final Contractor Report; PBD: Jul 1995
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; NICKEL ALLOYS; STRAIN AGING; ALUMINIUM ALLOYS; INTERMETALLIC COMPOUNDS; POLYCRYSTALS; MONOCRYSTALS; STRAIN RATE; INTERSTITIALS; TEMPERATURE RANGE 0273-0400 K; TEMPERATURE RANGE 0400-1000 K; TEMPERATURE RANGE 1000-4000 K; NITROGEN ADDITIONS; TITANIUM ADDITIONS; CARBON ADDITIONS

Citation Formats

Weaver, M L. Investigation of strain aging in the ordered intermetallic compound beta-NiAl. Ph.D. Thesis final contractor report. United States: N. p., 1995. Web.
Weaver, M L. Investigation of strain aging in the ordered intermetallic compound beta-NiAl. Ph.D. Thesis final contractor report. United States.
Weaver, M L. 1995. "Investigation of strain aging in the ordered intermetallic compound beta-NiAl. Ph.D. Thesis final contractor report". United States.
@article{osti_161013,
title = {Investigation of strain aging in the ordered intermetallic compound beta-NiAl. Ph.D. Thesis final contractor report},
author = {Weaver, M L},
abstractNote = {The phenomenon of strain aging has been investigated in polycrystalline and single crystal NiAl alloys at temperatures between 300 and 1200 K. Static strain aging studies revealed that after annealing at 1100 K for 7200 s (i.e., 2h) followed by furnace cooling, high purity, nitrogen-doped and titanium-doped polycrystalline alloys exhibited continuous yielding, while conventional-purity and carbon-doped alloys exhibited distinct yield points and Luders strains. Prestraining by hydrostatic pressurization removed the yield points, but they could be reintroduced by further annealing treatments. Yield points could be reintroduced more rapidly if the specimens were prestrained uniaxially rather than hydrostatically, owing to the arrangement of dislocations into cell structures during uniaxial deformation. The time dependence of the strain aging events followed a t(exp 2/3) relationship suggesting that the yield points observed in polycrystalline NiAl were the result of the pinning of mobile dislocations by interstitials, specifically carbon. Between 700 and 800 K, yield stress plateaus, yield stress transients upon a ten-fold increase in strain rate, work hardening peaks, and dips in the strain rate sensitivity (SRS) have been observed in conventional-purity and carbon-doped polycrystals. In single crystals, similar behavior was observed; in conventional-purity single crystals, however, the strain rate sensitivity became negative resulting in serrated yielding, whereas, the strain rate sensitivity stayed positive in high purity and in molybdenum-doped NiAl. These observations are indicative of dynamic strain aging (DSA) and are discussed in terms of conventional strain aging theories. The impact of these phenomena on the composition-structure-property relations are discerned.},
doi = {},
url = {https://www.osti.gov/biblio/161013}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1995},
month = {7}
}

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