Dislocation Link Length Distributions During Harper-Dorn Creep of Monocrystalline Aluminum

Lee, S.; Ardell, A.J.

doi:10.1016/b978-0-08-031642-0.50118-5

Cited by 6 publications

(1 citation statement)

References 9 publications

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“…There is also indirect evidence from these experiments that purity may play a role because Harper-Dorn creep was not observed in samples of 99.99% purity with a high dislocation density but Harper-Dorn flow was revealed in very high purity 99.9995% Al with a low initial dislocation density of 10 8 m -2 . However, the evidence for a purity effect tends to be negated by the subsequent work of Lee and Ardell [33], conducted at the University of California, Los Angeles, where excellent agreement was obtained with the behavior anticipated for Harper-Dorn creep in experiments conducted on single crystals of Al of 99.99% purity with the crystals tested in compression using parallelepiped samples with an acceptable aspect ratio of 2. As already noted, the later work of Blum and Maier [19] in Germany, where Harper-Dorn creep was not observed in 99.99% purity Al single crystals, is inconclusive because the tests were conducted on compression samples using an unacceptably low aspect ratio of~1 where it is reasonable to anticipate, as indeed reported, that the measured strain rates will be exceptionally low by comparison with the rates anticipated for the Harper-Dorn process.…”

Section: Experimental Evidence On Metals In the Regime Anticipated Fomentioning

confidence: 79%

Fifty years of Harper–Dorn creep: a viable creep mechanism or a Californian artifact?

2007

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Fifty years ago, in a series of classic creep experiments conducted at the University of California in Berkeley, Harper and Dorn obtained unique experimental data revealing the possibility of a new and heretofore unrecognized flow process occurring in pure aluminum when tested at low stresses and at temperatures very close to the melting temperature. This flow mechanism, subsequently designated Harper-Dorn creep, has been the center of much argument and speculation in the ensuing years. The present paper looks back over the last half-century and charts the various developments in attempts to obtain a more detailed understanding of whether Harper-Dorn creep is (or is not) a viable creep process. Examples are presented for both metals and non-metals. It is concluded that, although it appears Harper-Dorn creep may occur only under restricted conditions associated with high purity materials and low initial dislocation densities, nevertheless there is good evidence supporting the validity of this creep mechanism as a viable and unique flow process.

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Section: Experimental Evidence On Metals In the Regime Anticipated Fomentioning

confidence: 79%