Change in creep mechanism of B.C.C. metals at transition from low to high temperatures

Myshlyaev, М. M.; Stepanov, W. A.; Шпейзман, В. В.

doi:10.1002/pssa.2210080206

Cited by 18 publications

(4 citation statements)

References 11 publications

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“…At a temperature of 673 K, in the low-stress range, their observations correspond to an activation volume of 9.7 × 10 −28 m 3 or 82 atomic volumes, smaller than that of Andrade's observations, but still large. The re-plotting by Siethoff and Ahlborn [10] of the observations of Myshlyaev et al [11] similarly shows two (or possibly three) regions of exponential dependence.…”

Section: The Activation Volumementioning

confidence: 79%

“…Moreover, the results of different observations do not seem to be compatible. Andrade [12] found an exponential dependence of creep rate on stress for polycrystalline copper in the stress range 5-11 MPa at 683 K while Myshlyaev et al [11] found a clear power-law dependence of the creep rate for polycrystalline copper at 673 K in the same stress range. If in fact the regimes of power-law creep and power-law breakdown are physically distinct, it is not clear to which of these regions the observations of the Andrade group refer.…”

Section: The Evidence From Metallographymentioning

confidence: 99%

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Do we have an acceptable model of power-law creep?

Nabarro

2004

Materials Science and Engineering: A

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Three models of power-law creep are frequently presented. Those of Weertman assume distributed sources of dislocations which spread until they meet dislocations from other sources. They then annihilate by bulk diffusion. If the density of sources is independent of stress, a 9/2 power law follows, but the creep rate is grossly less than that observed. Moreover, the more plausible assumption of a source density proportional to the cube of the stress leads to the conventional power law of 3. The model of Spingarn and Nix assumes dislocation glide with pile-ups at the grain boundaries. These cause steps on the boundaries, which are removed by grain-boundary diffusion. A fifth power law follows. The agreement in absolute creep rate shown in the original paper arises from a misreading of the tabulated data, and the true predicted creep rate is again far too low. Vacancy diffusion along dislocation cores in the interior of the grains is not likely to dominate grain-boundary diffusion, because the cross section of the dislocation network exceeds that of the grain boundary material only at large grain sizes. While Mecking and Estrin have shown that the vacancy concentration produced mechanically even in dislocation cell walls is likely to exceed that in thermal equilibrium only below 1/2 T m , it seems possible that the highly mobile interstitials produced mechanically may migrate along dislocations of secondary glide systems to allow vacancy and interstitial dipoles of the primary system to annihilate mutually, with a probable power law of 5. However, the observations of Andrade and of Hanson, which may apply to the regime of power-law breakdown rather than power-law creep, strongly indicate that deformation is localized at the grain boundaries. If this is the case, existing theories of power-law creep based on models of homogeneous deformation are irrelevant; alternatively, the regimes of power-law creep and power-law breakdown must be treated separately.

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Section: The Activation Volumementioning

confidence: 79%

Section: The Evidence From Metallographymentioning

confidence: 99%

Do we have an acceptable model of power-law creep?

Nabarro

2004

Materials Science and Engineering: A

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“…During tension deformation, the potential barrier height U signifi cantly exceeds the potential barrier height V corre sponding to torsional deformation. For example, in the case of aluminum, U = 2.2-2.3 eV [6][7][8][9] and V = 1.2 eV [10]. The barrier U corresponds to dislocation intersection with the formation of interstitial defects [5], while the physical meaning of the barrier V Note: Here and in Table 2, i and v mean interstitial and vacancy thresholds, k and p are fractions of formed interstitial and vacancy thresholds, respectively.…”

Section: Intersection Of Screw Dislocations In Fccmentioning

confidence: 98%

Intersection of screw dislocations in fcc crystals during torsional deformation

Myshlyaev

2012

Dokl. Phys.

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“…Three different regimes may be distinguished. Regime I11 occurring at high stresses and extending at least down to room temperature [8] has been interpreted by a cross-slip mechanism [9]. I) Am Hubland, W-8700 Wurzburg, FRG.…”

Section: Introductionmentioning

confidence: 99%

Steady-state deformation of copper solid-solution alloys

Siethoff

1992

Phys. Stat. Sol. (a)

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The plasticity of copper solid solutions exhibits unusual properties, which are not yet understood. Two basically different classes may be distinguished. Alloys of the first type behave similarly as “normal” metallic solid solutions such as AlMg, the steady‐state deformation characteristics of which are more or less established in the literature. The second type shows properties as pure metals although, according to the material parameters involved, typical alloy effects should be expected. It is shown that these two classes of copper solid solutions are characterized by a different magnitude of the atomic misfit between solute and solvent atoms. Such an effect is not known for the “normal” metallic alloys. The peculiarities in the deformation behavior of pure copper are discussed in this context. Nickel solid solutions are also discussed.

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Change in creep mechanism of B.C.C. metals at transition from low to high temperatures

Abstract: The creep behaviour of Cu, Al, and Pb has been studied in a wide range of temperatures and stresses. A change both in dislocation structure and creep characteristics has been found which indicates the change in creep mechanism as the temperature rises and the applied stress decreases.

Cited by 18 publications

References 11 publications

Do we have an acceptable model of power-law creep?

Do we have an acceptable model of power-law creep?

Intersection of screw dislocations in fcc crystals during torsional deformation

Steady-state deformation of copper solid-solution alloys

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