An Evaluation of Power Law Breakdown in Metals, Alloys, Dispersion Hardened Materials and Compounds

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Creep at high stresses often produces strain rates that exceed those that would be predicted by a power law relationship. In this paper, we examine available high stress creep data for pure metals, solid solution alloys, dispersion strengthened powder metallurgy materials and compounds for power law breakdown (PLB). The results show that, if PLB is observed, then the onset of PLB is generally observed at about {epsilon}/D{sub eff} = 10{sup 13} m{sup -2}, where D{sub eff} is the effective diffusion coefficient incorporating lattice and dislocation pipe diffusion. The common origins of PLB for the various systems studied can be found ... continued below

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349 Kilobytes pages

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Lesuer, D.R.; Syn, C.K. & Sherby, O.D. October 20, 1999.

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Creep at high stresses often produces strain rates that exceed those that would be predicted by a power law relationship. In this paper, we examine available high stress creep data for pure metals, solid solution alloys, dispersion strengthened powder metallurgy materials and compounds for power law breakdown (PLB). The results show that, if PLB is observed, then the onset of PLB is generally observed at about {epsilon}/D{sub eff} = 10{sup 13} m{sup -2}, where D{sub eff} is the effective diffusion coefficient incorporating lattice and dislocation pipe diffusion. The common origins of PLB for the various systems studied can be found in the production of excess vacancies by plastic deformation. Anomalous behavior in two pure metals (nickel and tungsten) and a solid solution alloy (Fe-25Cr and Fe-26Cr-1Mo) has been analyzed and provides insight into this excess vacancy mechanism. In metal systems, the onset of PLB is related to a change in the nature of the subgrain structure developed. In the PLB region, subgrains become imperfect containing dislocation tangles adjacent to the sub-boundary, and dislocation cells are evident. The dislocation tangles and cells are the source of excess vacancies and increase the creep rate above that predicted from power law creep. If subgrains do not form then PLB is not observed. In solid solution alloys, in which the dominant deformation resistance results from the interaction of solute atoms with moving dislocations, excess vacancies influence the diffusion of these solute atoms. PLB is not observed in many systems. This is attributed either to the presence of a high equilibrium vacancy concentration (because of a low activation energy for vacancy formation) or to the inability to form subgrains.

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349 Kilobytes pages

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  • Honorary Symposium for Professor Oleg Sherby, Nashville, TN (US), 03/16/2000--03/20/2000

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  • Report No.: UCRL-JC-135191
  • Grant Number: W-7405-Eng-48
  • Office of Scientific & Technical Information Report Number: 791669
  • Archival Resource Key: ark:/67531/metadc734982

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  • October 20, 1999

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  • Oct. 19, 2015, 7:39 p.m.

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  • May 6, 2016, 1:18 p.m.

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Lesuer, D.R.; Syn, C.K. & Sherby, O.D. An Evaluation of Power Law Breakdown in Metals, Alloys, Dispersion Hardened Materials and Compounds, article, October 20, 1999; California. (digital.library.unt.edu/ark:/67531/metadc734982/: accessed August 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.