Strain localization in nickel single crystals cyclically deformed at 77 K

Hollmann, Martin

doi:10.1080/09500830050134327

Cited by 6 publications

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“…An important result of the AFM measurements is that in the y pa range investigated the averaged strain y SB in a specimen is independent of the imposed plastic strain amplitude. The value of f SB is about three times larger than the plateau strain limit y'^ = 2.510 2 (Hollmann 2000), which is also marked in Figure 7 (dashed line). Considering all imposed strain amplitudes one obtains y SB = 7.5 -10~2.…”

Section: Slip Activitymentioning

confidence: 67%

Cyclic Plasticity of Nickel Single Crystals Fatigued at Cryogenic Temperatures

Hollman¹

2002

Journal of the Mechanical Behavior of Materials

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Nickel monocrystals oriented for single slip have been cyclically deformed at 77 Κ in the range of plastic strain amplitudes between 1.4-10" 4 and 3.5-10 " 2 up to saturation of the stress amplitude. Special attention is paid to a comparison of slip and dislocation structure phenomena observed in fatigue tests at 77 Κ and those found after cycling at room temperature and elevated temperatures. The dislocation structure has been investigated on different length scales. Using the channelling contrast technique of the scanning electron microscope as well as bright field-as weak-beam imaging technique in the transmission electron microscope, a systematic study of the dislocation structure was carried out in order to describe quantitatively the influence of the imposed plastic strain amplitude on structure parameters of 77 Ä^-deformed nickel single crystals. It turns out that nickel single crystals cyclically deformed at 77 Κ show no typical "two phase structure" consisting of persistent slip bands and matrix regions like fee metals deformed at higher deformation temperatures but they evolve a nearly "homogeneous" dislocation structure. At 77 Κ the strain is localized in narrow slip bands in the same way as at higher temperatures, although there is no indication of a "two-phase" structure. From the experimental findings it is concluded that Winter's "two-phase" model remains valid, when averaging the plastic strain values over all slip bands and over a sufficient number of cycles.

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Section: Slip Activitymentioning

confidence: 67%