The role of Harper–Dorn creep at high temperatures and very low stresses

Kumar, Praveen; Kassner, M.E.; Langdon, Terence G.

doi:10.1007/s10853-008-2680-4

Cited by 12 publications

(6 citation statements)

References 35 publications

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“…As a mentioned earlier, a stress exponent higher than unity (n = 3) was very recently reported [26] for Harper-Dorn creep in Al single crystals of high purity (99.999 pct).…”

Section: A Stress Dependence Of Harper-dorn Creepmentioning

confidence: 56%

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Uncovering the Mystery of Harper–Dorn Creep in Metals

Cheng

Chauhan

Mohamed

2008

Metall Mater Trans A

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In the present investigation, the occurrence of Harper-Dorn creep in Pb was studied under the condition of large strains. In performing the study, two Pb grades, commercial-purity Pb (99.95 pct) and high-purity Pb (99.999 pct), were creep tested at 573 K. The mechanical data showed that 99.95 Pb, unlike 99.999 Pb, did not exhibit accelerated creep rates at stresses <0.1 MPa (the region of Harper-Dorn creep). Also, the data on 99.999 Pb revealed that the creep curves associated with Harper-Dorn creep exhibited periodic accelerations and that the stress exponent was approximately 3, not unity as previously reported for Pb and other materials. An examination of the substructure developed during creep revealed that the substructural details in 99.95 Pb were markedly different from those characterizing Harper-Dorn creep in 99.999 Pb. In 99.95 Pb, the substructural observations included the presence of very large subgrains and triple junctions of subgrains. By contrast, in 99.999 Pb, the substructural features included the nucleation of new grains and the presence of twins. Combining the present data on Pb and those reported recently for Al has led to three important conclusions. First, the accelerated creep rates noted in the region of Harper-Dorn creep are produced by a creep process for which the dominant restoration mechanism is dynamic recrystallization. Second, the linear-stress dependence of creep rate previously reported for Harper-Dorn creep is most probably a direct consequence of short-term measurements involving small strains (total creep strains £0.01). Finally, Harper-Dorn creep will be observed in a large-grained metal at very low stresses if its purity level is high. This condition favors dynamic recrystallization as a restoration mechanism.

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“…As a mentioned earlier, a stress exponent higher than unity (n = 3) was very recently reported [26] for Harper-Dorn creep in Al single crystals of high purity (99.999 pct).…”

Section: A Stress Dependence Of Harper-dorn Creepmentioning

confidence: 56%

“…This value for the stress exponent of Harper-Dorn creep in 99.999 Pb is similar to those reported for polycrystalline high-purity Al [19] and, most recently, single crystals of high-purity Al in the region of Harper-Dorn creep. [26] C. Substructure…”

Section: B Stress Dependence Of the Steady-state Creep Ratementioning

confidence: 99%

Uncovering the Mystery of Harper–Dorn Creep in Metals

Cheng

Chauhan

Mohamed

2008

Metall Mater Trans A

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“…Creep data for tests performed on very high purity single crystals at 913 K showing that the stress exponent is about 3 not 1 in the region of Harper–Dorn. Reproduced with permission . Copyright 2019, Springer.…”

Section: Discussionmentioning

confidence: 99%

“…Recent results by Kumar et al [36] showed that while the creep data for high-purity single crystals of Al (99.999%) exhibited a stress exponent of 3 in the Harper-Dorn domain (Figure 9), which is consistent with that reported by Ginter et al [33] for high-purity polycrystalline Al of 99.999% (stress exponent %2.5-3), the results on oligocrystalline Al samples of 99.97 % obeyed power law creep with a stress exponent of 5 (climb-controlled creep) even at the lowest stresses; the latter behavior in general agrees with results by Ginter and Mohamed, [20,33] reported for commercial purity Al of 99.99% (Harper-Dorn is not observed).…”

Section: Harper-dorn Creepmentioning

confidence: 96%

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Creep and Superplasticity: Evolution and Rationalization

Mohamed

2020

Adv Eng Mater

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Detailed studies on the creep behavior of materials are of scientific and practical significance. From a scientific point of view, data obtained from such studies are critical to the characterization of creep behavior in terms of deformation mechanisms. From a practical point of view, information inferred from such studies is useful because of its relevance to many design considerations. Over the past several decades, much progress has been made in rationalizing the creep behavior of metals and solid‐solution alloys. Such progress is extended to understanding the creep behavior of new classes of materials such as powder metallurgy (PM) Al alloys, discontinuous SiC composites, superplastic alloys, and high‐entropy alloys (HEAs). Progress in micrograin superplasticity (1 μm < d < 10 μm, where d is the grain size) has been applied to the emergence of high strain rate (HSR) superplasticity using ultrafine‐grained alloys (0.3 μm < d < 1 μm). The concept of creep is utilized to develop a deformation mechanism for nanocrystalline (nc) materials (d < 100 nm). Using the details of this mechanism, it is possible (1) to explain why the behavior of nc material is not superplastic and 2) to predict a transition from superplastic behavior to nc behavior.

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