Indentation induced dislocation nucleation: The initial yield point

Gerberich, William W; Nelson, John; Lilleodden, Erica T.; Anderson, Peter M.; Wyrobek, Jerzy T.

doi:10.1016/1359-6454(96)00010-9

Cited by 390 publications

(179 citation statements)

References 18 publications

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“…3 was determined to be 1.8 GPa. If one compares this with the two model calculations in Table 2, the homogeneous dislocation loop model [13] is about a factor of two low and the unstable stacking model using straight dislocations [12], about a factor of three high.…”

Section: Dislocation Nucleationmentioning

confidence: 99%

Nanoindentation-induced defect–interface interactions: phenomena, methods and limitations

et al. 1999

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AbstractÐNanoindentation for measuring thin ®lm mechanical properties is probably the most popular yet ill-understood method due to its inherent complexities. As opposed to burst pressure or microtensile tests of lithographed structures, where relatively uniform stress ®elds may be generated, the indentation-induced stress gradients can produce unique challenges. Because of the test's simplicity and ability to mechanically probe the smallest of scales, it is becoming increasingly applied. Five possible stages of deformation are suggested from Hertzian elastic to ®lm delamination and double buckling. In particular metal ®lms on harder substrates are emphasized where it is shown that dislocation nucleation and arrest are only partially understood. Later stages of ®lm delamination are illustrated with Cu/SiO 2 /Si where it is shown that the true work of adhesion is 0.6 J/m 2 . Current limitations of indentation-induced delamination measures of toughness involve large scatter associated with sensitivity of the fracture radius to the contact radius ratio.

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Section: Dislocation Nucleationmentioning

confidence: 99%

Nanoindentation-induced defect–interface interactions: phenomena, methods and limitations

et al. 1999

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“…[8][9][10] Size effects are observed for pristine crystals, as well. 11,12 In the earliest stages of nanoindentation, for example, the crystal volume is extremely small and can be dislocation-free, requiring very large stresses to nucleate new dislocations. In addition, classic experiments on the initially dislocation-free metal whiskers indicated that whiskers with smaller diameters yielded at higher stresses.…”

mentioning

confidence: 99%

“…[1][2][3][4][5][6] Pure metals and some alloys exhibit strong size effects at the submicron scale. [1][2][3][4][5][6][7][8][9][10][11][12][13] Size effects in indentation, torsion, and bending have been understood in terms of the nonuniformity of the deformation, which sets up strain gradients leading to hardening. 7 Size effects are also found in thin films, where the strength scales inversely with film thickness and is usually attributed to the confinement of dislocations by the substrate.…”

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confidence: 99%

Nanoscale gold pillars strengthened through dislocation starvation

2006

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It has been known for more than half a century that crystals can be made stronger by introducing defects into them, i.e., by strain-hardening. As the number of defects increases, their movement and multiplication is impeded, thus strengthening the material. In the present work we show hardening by dislocation starvation, a fundamentally different strengthening mechanism based on the elimination of defects from the crystal. We demonstrate that submicrometer sized gold crystals can be 50 times stronger than their bulk counterparts due to the elimination of defects from the crystal in the course of deformation. DOI: 10.1103/PhysRevB.73.245410 PACS number͑s͒: 62.25.ϩg, 81.07.Bc, 81.16.Rf, 81.70.Bt Anyone who has ever repeatedly bent a copper wire knows that it gets progressively stronger as it becomes more deformed, through a phenomenon called strain-hardening. The strengths of cold-worked metals are known to be up to ten times greater than those of well-annealed crystals. Plasticity in metals occurs by the motion of dislocations, or line defects, which multiply in the course of plastic deformation. Impeding the motion of dislocations by introducing defects into crystals results in strengthening. Although these fundamental concepts are often assumed to be applicable to crystals of any dimensions, numerous recent studies have shown that conventional plasticity diverges at a certain length scale, with smaller samples reported to be stronger than their bulk counterparts. [1][2][3][4][5][6] Pure metals and some alloys exhibit strong size effects at the submicron scale. [1][2][3][4][5][6][7][8][9][10][11][12][13] Size effects in indentation, torsion, and bending have been understood in terms of the nonuniformity of the deformation, which sets up strain gradients leading to hardening. 7 Size effects are also found in thin films, where the strength scales inversely with film thickness and is usually attributed to the confinement of dislocations by the substrate. [8][9][10] Size effects are observed for pristine crystals, as well. 11,12 In the earliest stages of nanoindentation, for example, the crystal volume is extremely small and can be dislocation-free, requiring very large stresses to nucleate new dislocations. In addition, classic experiments on the initially dislocation-free metal whiskers indicated that whiskers with smaller diameters yielded at higher stresses. 13 In typical whiskerlike deformation behavior, initial elastic loading leads to a very high stress followed by a significant drop and continued plastic flow at low stresses. Finally, several molecular dynamics simulations 14-16 and more recent experiments on small pillars 17,18 all support the tenet that smaller is stronger. In spite of much progress on size effects research there is still no unified theory for plastic deformation at the submicron scale.We focus on size effects arising in unconstrained geometries, in the absence of strain gradients, and with nonzero initial dislocation densities. Gold nanopillars ranging in diameter between 200 nm and s...

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“…The apparent decrease of the contact pressure under the maintained constant rate of displacement increase is tantamount to the pop-in observed during nanoindentation experiments [17][18][19]. Pop-in, alternatively referred to as the yield point, marks the onset of plasticity in defectfree crystals [17][18][19]. For load controlled experiments, pop-in appears as rapid displacement increase whereas its incidence under displacement control is evident as a load drop [20].…”

Section: Resultsmentioning

confidence: 98%

“…Then the contact pressure continues to gradually decrease approaching hardness (H) of bulk Si at ≈ 12 GPa [9]. The apparent decrease of the contact pressure under the maintained constant rate of displacement increase is tantamount to the pop-in observed during nanoindentation experiments [17][18][19]. Pop-in, alternatively referred to as the yield point, marks the onset of plasticity in defectfree crystals [17][18][19].…”

Section: Resultsmentioning

confidence: 99%

Influence of Phase Transformations on Incipient Plasticity of Si-Nanospheres

Chrobak

Nowak

2017

Acta Phys. Pol. A

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Our finding of the current spike effect highlighted for the first time in 2009 offers an enhanced understanding of the link between nanoscale mechanical deformation and electrical behavior, and ultimately suggests key advances in unique phase-change applications in future electronics. Certainly, crystal imperfections affect the properties of the nanoparticles themselves, e.g., their biocompatibility and biodegradability. The potential role of dislocations having a profound impact on the use of Si nanoparticles was largely overlooked, since plastic deformation of bulk Si is dominated by amorphization and phase transformations. Here we show an effect of bulk → nanoparticle transition (deconfinement) on incipient plasticity of Si-nanovolume. Our results provide a fresh insight into the dilemma concerning dislocation or phase transformation origin of nanoscale plastic deformation of semiconductor nanoobjects.

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Indentation induced dislocation nucleation: The initial yield point

Cited by 390 publications

References 18 publications

Nanoindentation-induced defect–interface interactions: phenomena, methods and limitations

Nanoindentation-induced defect–interface interactions: phenomena, methods and limitations

Nanoscale gold pillars strengthened through dislocation starvation

Influence of Phase Transformations on Incipient Plasticity of Si-Nanospheres

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