Dislocation motion in icosahedral quasicrystals at elevated temperatures: Numerical simulation

Schaaf, Gunther; Roth, Johannes; Trebin, Hans‐Rainer

doi:10.1080/0141861031000113352

Cited by 9 publications

(8 citation statements)

References 22 publications

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“…So dislocation emission in the three-dimensional icosahedral quasicrystal modelled here should be less likely than in the two-dimensional decagonal model quasicrystal. Very high stresses are indeed needed to move dislocations in our model quasicrystal in molecular dynamics simulations 25 .…”

Section: Discussionmentioning

confidence: 95%

“…Third, the Lennard-Jones potentials used 23,24 keep the model stable even under strongest mechanical deformations or irradiation (introduction of point defects) and have been used in our group in many simulations of dislocation motion 25 or even shock waves 26 . The structure is robust under a wide variation of the potential depths.…”

Section: B Molecular Dynamics Techniquementioning

confidence: 99%

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Dynamic fracture of icosahedral model quasicrystals: A molecular dynamics study

et al. 2005

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Ebert et al. Phys. Rev. Lett. 77, 3827, 1996 have fractured icosahedral Al-Mn-Pd single crystals in ultrahigh vacuum and have investigated the cleavage planes in situ by scanning tunneling microscopy (STM). Globular patterns in the STM images were interpreted as clusters of atoms. These are significant structural units of quasicrystals. The experiments of Ebert et al. imply that they are also stable physical entities, a property controversially discussed currently. For a clarification we performed the first large-scale fracture simulations on three-dimensional complex binary systems. We studied the propagation of mode-I cracks in an icosahedral model quasicrystal by molecular dynamics techniques at low temperature. In particular we examined how the shape of the cleavage plane is influenced by the clusters inherent in the model and how it depends on the plane structure. Brittle fracture with no indication of dislocation activity is observed. The crack surfaces are rough on the scale of the clusters, but exhibit constant average heights for orientations perpendicular to high-symmetry axes From detailed analyses of the fractured samples we conclude that both the plane structure and the clusters strongly influence dynamic fracture in quasicrystals and that the clusters therefore have to be regarded as physical entities

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Section: Discussionmentioning

confidence: 95%

Section: B Molecular Dynamics Techniquementioning

confidence: 99%

Dynamic fracture of icosahedral model quasicrystals: A molecular dynamics study

et al. 2005

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“…The behavior of the crystal and the quasicrystal models in shock wave simulations is similar to the behavior of ionic materials: slippage is hindered by the creation of high-energy anti-phase boundaries. Dislocations are slow, rare and high energies are needed to generate them 25 . The single-crystal ionic materials break into many crystallites and form broad defect bands 26 .…”

Section: Discussionmentioning

confidence: 99%

Shock waves in complex binary solids: Cubic Laves crystals, quasicrystals, and amorphous solids

Roth

2005

Phys. Rev. B

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Shock waves have been simulated by molecular dynamics in the cubic Laves phase C15, in related Frank-Kasper-type (AlCu)Li quasicrystals, and in an amorphous solid of the same composition and potential parameters. The goal of this study was to generate shock waves in periodic and aperiodic structures and to compare their behavior. The expectation was that new types of defects would show up in aperiodic materials. Three regimes are observed in the Laves phase: at low shock wave intensity the system reacts elastically, at high intensities it turns disordered. In the intermediate region the velocity of the elastic wave saturates and an additional plastic wave appears. Extended defects are created which form a network of walls of finite width. The crystallites in between are rotated by the shock wave. If the samples are quenched a polycrystalline phase is obtained. The size of the grains decreases with increasing shock wave intensity until complete fragmentation occurs in the third regime. The behavior of the quasicrystal models is similar, except that there is a continuous transition from a quasi-elastic behavior to the plastic regime. Ring processes are observed which break up into open paths when the shock wave energy grows. The transition to a complete destruction of the structure is continuous. In the amorphous solid a linear us − up-relation is found over the whole range of piston velocities. Two regimes are present, with unsteady plastic waves at weak shock strengths and steady waves in the range coinciding with the upper regime in the ordered structures.

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“…In simulations of three-dimensional icosahedral quasicrystals, however, it is very hard to create and drive dislocations. 11 Perfect brittle fracture without dislocation activity is observed in numerical experiments. 9 Thus, the suggested nanoplastic behavior seems unlikely in i-AlPdMn.…”

mentioning

confidence: 93%

Comment on “Cleaved surface ofi-AlPdMnquasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness”

Rösch

Trebin

2008

Phys. Rev. B

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Quasicrystals are intermetallic compounds with long-range quasiperiodic translational order, composed of atomic clusters, which can be interpreted as basic geometric building blocks. It is a persistent discussion whether these clusters also represent physical entities. Cleavage planes of fractured icosahedral AlPdMn as well as sputtered surfaces annealed up to about 900 K are rough with clusterlike protrusions. Fivefold surfaces annealed at higher temperatures exhibit flat terraces. Thus, obviously, the clusters cannot be termed supermolecules. However, experiments and numerical simulations indicate that fracture is influenced by the clusters. Thus, they determine physical properties. In a recent paper, Ponson et al. ͓Phys. Rev. B 74, 184205 ͑2006͔͒ investigated experimental fracture surfaces of AlPdMn and questioned the signature of the clusters. In this comment, we study the self-affinity of cleavage planes obtained by molecular-dynamics simulations. We conclude that the findings of Ponson et al. are not excluding a physical role of the clusters in quasicrystals.One method to analyze the roughness of fracture surfaces is to calculate the height-height correlation functions. These reveal scaling properties ͑see Ref. 1 for a review paper͒ with a "universal" roughness exponent of about 0.8 for a wide range of materials. However, up to now, no theoretical model is able to satisfactorily capture this self-affinity. Thus, it is hard to interpret microscopic properties of the investigated structures starting from the scaling behavior. It might even not be possible to distinguish a fractured from a sputtered surface, as the roughness exponents of both surfaces can lie in the same range. 2,3 Although the scaling behavior of fracture surfaces seems to be universal, the range of length scales in which it is valid may strongly vary for different materials. It has been argued that the corresponding cut-off length is related to the size of the process zone R c . 4 Inside this region, linear elastic predictions do not fit the real deformation field. Such a nonlinear and dissipative zone always exists, as atomic bonds break at the crack tip. The behavior on and below this scale determines whether, how, and where a crack travels. R c should therefore be related to the microstructure. In the following, we investigate the role and interpretation of for fracture surfaces of icosahedral quasicrystals. The roughness of i-AlPdMn fracture surfaces was analyzed in a recent paper by Ponson et al. 5 They found scaling properties which resemble those of various disordered materials. The height-height correlation function reveals a selfaffine behavior from the atomic scale up to Ϸ 2 nm. The corresponding Hurst exponent H is found to be about 0.72 ͑see Fig. 2 of Ref. 5͒. The authors pointed out that the selfaffine region includes the radius of the clusters r c Ϸ 0.5 nm, which are inherent in the structure. It is stated that the morphology of the fracture surfaces therefore does not reflect the cluster distribution. Thus, the influence of th...

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Dislocation motion in icosahedral quasicrystals at elevated temperatures: Numerical simulation

Cited by 9 publications

References 22 publications

Dynamic fracture of icosahedral model quasicrystals: A molecular dynamics study

Dynamic fracture of icosahedral model quasicrystals: A molecular dynamics study

Shock waves in complex binary solids: Cubic Laves crystals, quasicrystals, and amorphous solids

Comment on “Cleaved surface ofi-AlPdMnquasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness”

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