Mechanical instabilities in extended solid solutions near the crystal-to-glass transition

Ettl, C.; Samwer, K.

doi:10.1016/0921-5093(94)90550-9

Cited by 22 publications

(5 citation statements)

References 32 publications

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“…63 Similar features have been observed in other metallic systems when atomic solubility was forced beyond its equilibrium limit by the use of far-from equilibrium methods. A large decrease in the Debye temperature (calorimetric measurements) was reported in Zr(Al) solid solutions obtained from ball milling or melt quenching; 64 we previously observed elastic softening of the shear constant (BLS measurements) of Mo(Ni) and Ni(Mo) thin films deposited by ion sputtering. 3 It is interesting to note that the same behavior may be observed when chemical and topological disordering are continuously induced under ion irradiation in an intermetallic compound (Zr 3 Al).…”

Section: Sound Velocities and Effective Elastic Constantsmentioning

confidence: 88%

Lattice instability and elastic response of metastable Mo1−xSixthin films

et al. 2013

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We present a detailed experimental study on Mo 1−x Si x thin films, an archetypal alloy system combining metallic and semiconductor materials. The correlations between structure and elastic response are comprehensively investigated. We focus on assessing trends for understanding the evolution of elastic properties upon Si alloying in relation to the structural state (crystalline vs amorphous), bonding character (metallic vs covalent), and local atomic environment. By combining picosecond ultrasonics and Brillouin light scattering techniques, a complete set of effective elastic constants and mechanical moduli (B, G, E) is provided in the whole compositional range, covering bcc solid solutions (x < 0.20) and the amorphous phase (0.20 < x < 1.0). A softening of the shear and Young moduli and a concomitant decrease of the Debye temperature is revealed for crystalline alloys, with a significant drop being observed at x ∼ 0.2 corresponding to the limit of crystal lattice stability. Amorphous alloys exhibit a more complex elastic response, related to variations in coordination number, atomic volume, and bonding state, depending on Si content. Finally, distinct evolutions of the G/B ratio as a function of Cauchy pressure are reported for crystalline and amorphous alloys, enabling us to identify signatures of ductility vs brittleness in the features of the local atomic environment. This work paves the way to design materials with improved mechanical properties by appropriate chemical substitution or impurity incorporation during thin-film growth.

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Section: Sound Velocities and Effective Elastic Constantsmentioning

confidence: 88%

Lattice instability and elastic response of metastable Mo1−xSixthin films

et al. 2013

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“…Recently, Wang et al [9] derived modified stability conditions for the case of strained solids by including the hydrostatic pressure into the strain tensor, which becomes important close to the instability. The vanishing of elastic constants near the crystal to glass transition has been measured experimentally [10][11][12][13][14].…”

Section: Fig 4 Elastic Constants For Thementioning

confidence: 99%

Strain Rate Induced Amorphization in Metallic Nanowires

et al. 1999

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Using molecular dynamics simulations with a many-body force field, we studied the deformation of single crystal Ni and NiCu random alloy nanowires subjected to uniform strain rates but kept at 300 K. For all strain rates, the Ni nanowire is elastic up to 7.5% strain with a yield stress of 5.5 GPa, far above that of bulk Ni. At high strain rates, we find that for both systems the crystalline phase transforms continuously to an amorphous phase, exhibiting a dramatic change in atomic short-range order and a near vanishing of the tetragonal shear elastic constant perpendicular to the tensile direction. This amorphization which occurs directly from the homogeneous, elastically deformed system with no chemical or structural inhomogeneities exhibits a new mode of amorphization.[ S0031-9007(99) We used molecular dynamics (MD) simulations to strain fcc crystalline nanowires at a uniform rate along the ͗001͘ crystallographic direction [2][3][4]. Here, to realize an infinite nanowire we applied 1D periodic boundary condition in the c direction (an initial length of ten fcc unit cells, ഠ4 nm, while the a and b directions are five fcc cells long, ഠ2 nm). We studied the deformation behavior at constant strain rates (0.05% to 5% ps 21 ) and constant temperature (300 K). The tensile strain component´3 3 was applied uniformly (in increments of 0.5%) to obtain the specified strain rate. The average stress components s ij in the specimen were computed at and following each applied strain increment. At the strain rates reported here, the stress distribution relaxes between strain increments to a homogeneous stationary equilibrium state of uniaxial tensile stress. We observe a crystal to glass transformation at 300 K above a critical strain rate.Such large strain rates are observed experimentally only in shock wave and high velocity impact studies, where it has been difficult to control temperature or to obtain details about dynamic structural changes. Experiments at such high strain rates lead to shear localization arising from adiabatic heat dissipation and local thermal softening of the material, which results in highly nonequilibrium systems that are difficult to study experimentally. The MD simulations follow the effects of loading and loading rate independently from those arising from heat dissipation and concomitant temperature increases.To illustrate the effect of strain rate on the detailed deformation, Fig. 1 displays snapshots of MD simulations on an fcc NiCu random alloy nanowire (at 300 K) deformed to 100% strain at strain rates from 0.5% and 5% ps 21 in the z direction. For ᠨ 0.5% ps 21 cooperative shear events within the crystal produce coherent shear bands, which are often coherent "twins." Multiple coherent shearing events finally lead to necking before failure. For ᠨ 5% ps 21 , the behavior is fundamentally different. No coherent shear bands or twins form as the system is strained. Instead, the specimen transforms homogeneously to an amorphous state at strains of only 0.15. This homogeneously disordered material un...

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“…This confirms again the close similarity of such transitions in layered systems to the crystal-to-glass transition in bulk metallic alloys and compounds. 5,6 One may hypothesize that the structural transitions ͑␥-to ␣-phase-like, crystalline to amorphous͒ in the Ce layers are driven by interface effects. As has been emphasized before, 30 the structure of a multilayer is determined by a competition of the bulk crystal structure energies of the constituents and of the interface energies resulting from the differences in their lattice spacings or crystal symmetry.…”

Section: Discussionmentioning

confidence: 99%

“…This behavior reveals close similarities to the crystal-to-glass transition in bulk metallic alloys and compounds, which appears to be driven by a shear instability of the crystal lattice. 5,6 The flexural elastic response of the multilayers probed in the vibrating-reed experiments is dominated by the stiffer sublayers, i.e., essentially by the Fe component; contributions from the fcc-crystalline-toamorphous transition in the Ce layers, for example, could not be detected. In this paper we present results on the shear elastic response of the Ce/Fe multilayers probed by Brillouin light-scattering experiments.…”

Section: Introductionmentioning

confidence: 98%

Shear-elasticity anomaly in Ce/Fe multilayers

Haßdorf

Grimsditch

Felsch³

et al. 1997

Phys. Rev. B

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Brillouin light-scattering experiments have been performed at room temperature to determine the shear modulus C 44 of Ce/Fe multilayers ͑in their reference frame͒ as a function of the modulation wavelength ⌳. The study is complementary to a previous investigation of the flexural modulus E F of this system in the sense that, while E F is dominated by the Fe layers, C 44 largely reflects the elasticity of the more compliant Ce component. In the heterostructures, the Ce layers exhibit a laminated two-phase structure composed of low-volume ␣ and high-volume ␥-like Ce, with a thickness-dependent relative fraction. Furthermore, structural transitions occur from an amorphous phase to the crystalline phases of bcc Fe and fcc Ce, for Fe abruptly within the entire sublayer volume at a critical thickness near 20 Å, for Ce more gradually with increasing layer thickness starting near 40 Å. These structures and phase transitions are reflected in the variation of C 44 with ⌳. A large portion of this variation can be ascribed to the ⌳-dependent ␣-␥-like composite structure of the Ce layers. A superposed softening of C 44 is essentially the signature of the amorphous-to-crystalline transition in the Ce sublayers. ͓S0163-1829͑97͒02133-4͔

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Mechanical instabilities in extended solid solutions near the crystal-to-glass transition

Cited by 22 publications

References 32 publications

Lattice instability and elastic response of metastable Mo1−xSixthin films

Lattice instability and elastic response of metastable Mo1−xSixthin films

Strain Rate Induced Amorphization in Metallic Nanowires

Shear-elasticity anomaly in Ce/Fe multilayers

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