Mechanical behaviour of nanocrystalline iron and nickel in the quasi-static and low frequency anelastic regime

Bonetti, E.; Campari, Enrico Gianfranco; Bianco, L. Del; Pasquini, Luca; Sampaolesi, E.

doi:10.1016/s0965-9773(99)00359-1

Cited by 26 publications

(10 citation statements)

References 14 publications

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“…The empirical relationship between an,GB and T may not be explained by the Arrhenius relationship, and this issue will be mentioned later. On the other hand, Bonetti et al 23 reported that a strong stress relaxation of 10% for n-Fe specimens at 0.17T m and one of 6% for n-Ni at 0.18T m are observed in the as-prepared state. They also reported that an amount of the stress relaxation decreases to a few percent after annealing at 473 K, although no grain growth is detected after the annealing.…”

Section: Discussionmentioning

confidence: 98%

Characteristic creep behavior of nanocrystalline metals found for high-density gold

et al. 2002

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Nanocrystalline ͑n͒ Au specimens with a density of 19.4Ϯ0.2 g/cm 3 and a mean grain size of about 20 nm were prepared below 300 K by the gas deposition method, where two types of n-Au specimens were obtained as a function of a deposition rate, the type-H specimens above 800 nm/s and the type-L specimens below 800 nm/s. The anelastic and the plastic creep responses are similar qualitatively but different quantitatively between the type-H and type-L specimens. The anelastic strain an,GB , associated with the grain boundary ͑GB͒ regions, increases linearly with (TϪT an1)(ap Ϫ an1), when the temperature T is higher than a threshold temperature T an1 of 200 K and the applied stress ap is higher than a threshold stress, an1 , of a few MPa. The ratio of an,GB to the elastic strain is as large as 1.1 for the type-H specimens and 0.2 for the type-L specimens at 320 K for ap ӷ an1. The activation energy for the GB anelastic process is 0.2 eV. We surmise that cooperative motions of many atoms in the GB regions are responsible for an,GB , and both T an1 and an1 show a distribution depending on the number of atoms associated. The plastic creep rate Ј vs ap data show a letter S-like curve. We classified the creep response into three categories, region I for the linear creep rate region for ap between pc 1 and pc2 , region II for the transient creep rate region for ap between pc2 and pc3 , and region III for the saturation creep rate region for ap between pc3 and y. The threshold stresses pc1 and pc2 and the yield stress y are about 30, 150, and 360 MPa for the type-H specimens, and about 60, 300, and 500 MPa for the type-L specimens, respectively. pc3 is slightly lower than y. From scanning tunneling microscopy images, we surmise that the localized GB slip takes place in region I, and the mean separation between the localized GB slips decreases with increasing ap in region II and becomes comparable with the mean grain size in region III. The plastic creep in region III may be explained by the Ashby creep. The present view for the creep behavior explains the low-temperature creep behavior of fcc n metals.

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Section: Discussionmentioning

confidence: 98%

Characteristic creep behavior of nanocrystalline metals found for high-density gold

et al. 2002

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“…[10][11][12] A steep increase in the internal friction, Q À1 , of n-metals is observed at the temperature slightly higher than 300 K, where the activation energy estimated is also close to that reported for the GB diffusion in p-metals. [13][14][15][16][17][18][19][20] These results indicate that intrinsic natures of the GB regions in n-metals appear to be similar to those in p-metals.…”

Section: Introductionmentioning

confidence: 98%

Anelasticity Study on Motions of Atoms in the Grain Boundary Regions in Nanocrystalline Gold

2003

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High-density nanocrystalline (n-) Au was prepared by the gas deposition method. Various anelastic and plastic creep processes associated with the grain boundary (GB) regions were observed. The vibrating reed measurements at 10 2 Hz with strain amplitude of 10 À6 show a very broad internal friction peak near 95 K, Q À1 p,95 K , and a steep increase in the anelastic strain above 200 K, " a-I,>200 K . The tensile tests show a steep increase in the anelastic strain above 200 K, " a-II,>200 K , for the stress beyond a few MPa and a linear plastic creep strain above 200 K, " pc-1 , for stress range between 30 MPa and 150 MPa. The activation parameters, 1= 0 of 3 Â 10 11 s À1 and E of 0.16 eV, are found for Q À1 p,95 K , where 0 and E are a pre-exponential factor and an activation energy of the relaxation time . We surmise that simple relaxation processes are responsible for Q À1 p,95 K . The values of 1= 0 and E found for " a-I,>200 K and " a-II,>200 K decrease with increasing the applied stress or the temperature, indicating that their atomic processes are the same feather. Further, E found for " pc-1 is similar to or slightly smaller than that of " a-II,>200 K . These observations indicate that the atomic motions in the GB regions of n-Au develop in scale in the order of the underlying processes for " a-I,>200 K , " a-II,>200 K and " pc-1 , and are so different from those in the conventional polycrystalline Au.

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“…Recently, this method was used to investigate n-crystalline materials [11,12]. However, the internal friction of n-droplets, particularly n-Ga droplets, has not yet been reported.…”

Section: Introductionmentioning

confidence: 99%

Preparation and Internal Friction of Nanoscale Gallium Droplets

Huang

Fei

Shui

et al. 2002

phys. stat. sol. (a)

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A simple but effective method, ultrasonic vibration, has been used to prepare the nanoscale (hereafter n‐) Ga droplets. The n‐Ga droplets with average particle size of about 60–80 nm in diameter dispersed in polystyrenes (PS) have been successfully obtained. The low frequency internal friction of solid polystyrenes containing n‐Ga droplets was measured. We observed for the first time, that the internal friction peak caused by n‐Ga droplets appears around 313 K. The peak shifts to higher temperature with increasing frequency, indicating a relaxation peak. It is suggested that the internal friction peak is associated with the relaxation of n‐Ga droplets in the cavities of matrix under applied stress.

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Mechanical behaviour of nanocrystalline iron and nickel in the quasi-static and low frequency anelastic regime

Cited by 26 publications

References 14 publications

Characteristic creep behavior of nanocrystalline metals found for high-density gold

Characteristic creep behavior of nanocrystalline metals found for high-density gold

Anelasticity Study on Motions of Atoms in the Grain Boundary Regions in Nanocrystalline Gold

Preparation and Internal Friction of Nanoscale Gallium Droplets

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