Thermodynamic parallels between solid-state amorphization and melting

1990 ◽  
Vol 5 (2) ◽  
pp. 286-301 ◽  
Author(s):  
D. Wolf ◽  
P. R. Okamoto ◽  
S. Yip ◽  
J. F. Lutsko ◽  
M. Kluge
Keyword(s):  
Solid State ◽  
Amorphous Phase ◽  
Mechanical Instability ◽  
Extended Phase ◽  
Thermally Activated ◽  
Underlying Causes ◽  
Characteristic Features ◽  
Dynamics Simulations ◽  
Solid Liquid ◽  
State Amorphization

A thermodynamics-based description, in the form of an extended phase diagram, of melting and solid-state amorphization is proposed which brings out the parallels between these two phenomena and suggests that their underlying causes are apparently the same. Through molecular dynamics simulations we demonstrate that every crystal, in principle, can undergo two different types of melting transitions with characteristic features that are also observed in radiation- and hydrogenation-induced amorphization experiments on ordered alloys. The first type, defined in terms of free energies, is shown to involve the heterogeneous nucleation of the liquid or amorphous phase at extended lattice defects (such as grain boundaries, free surfaces, voids, or dislocations) and subsequent thermally-activated propagation of solid-liquid/amorphous interfaces through the crystal. The second type, arising from a mechanical instability limit described by Born, is homogeneous and does not require thermally-activated atom mobility. It is suggested that the role of chemical and structural disordering, a prerequisite for irradiation- but not hydrogenation-induced solid-state amorphization, is merely to drive the crystal lattice to a critical combination of volume and temperature at which the amorphous phase can form either heterogeneously or homogeneously.

Molecular Dynamics Simulation of the Effect of Interfaces in Melting and Solid-State Amorphization

1991 ◽  
Vol 230 ◽  
Author(s):  
Dieter Wolf ◽  
Sidney Yip
Keyword(s):  
Molecular Dynamics ◽  
Solid State ◽  
Dynamics Simulation ◽  
Elastic Behavior ◽  
Melting Transition ◽  
Extended Defects ◽  
Free Standing ◽  
Extended Phase ◽  
Characteristic Features ◽  
State Amorphization

AbstractA newly developed molecular dynamics code was used to study the effect of free surfaces, grain boundaries and voids in the process of melting. It was found that conventional “thermodynamic melting” occurs via nucleation of the liquid at the extended defects with subsequent growth into the crystal. In the absence of interfaces, or when this transition is kinetically hindered, however, a second type of melting transition can be triggered by an elastic instability first described by Born (“mechanical melting”). It is suggested that the distinct characteristic features associated with the two types of melting are actually observed in solid-state amorphization experiments. A unified thermodynamics-based description, in the form of an extended phase diagram, of melting and solid-state amorphization is proposed which brings out the parallels between these two phenomena and suggests that their underlying causes are apparently the same. By investigating the effect of surface stresses on the structure and elastic behavior of free-standing thin films, we discuss how these concepts need to be modified in thin-film and small-grained materials.

Solid state amorphization reactions in deformed Ni-Zr multilayered composites

1990 ◽  
Vol 5 (3) ◽  
pp. 488-497 ◽  
Author(s):  
G. C. Wong ◽  
W. L. Johnson ◽  
E. J. Cotts
Keyword(s):  
Thermal Stability ◽  
Solid State ◽  
Amorphous Phase ◽  
Equilibrium Phase ◽  
Solid State Reactions ◽  
Heat Of Mixing ◽  
Scanning Calorimetry ◽  
Multilayered Composites ◽  
State Amorphization ◽  
Thermal Stability Of

The mechanisms of metallic glass formation and competing crystallization processes in mechanically-deformed Ni-Zr multilayered composites have been investigated by means of differential scanning calorimetry and x-ray diffraction. Our investigation of the heat of formation of amorphous NixZr1−x alloys shows a large negative heat of mixing (on the order of 30 kJ/mole) for compositions near Zr55Ni45 with a compositional dependence qualitatively similar to that predicted by mean field theory. We find that the products of solid state reactions in composites of Ni and Zr can be better understood in terms of the equilibrium phase diagram and the thermal stability of liquid quenched metallic glasses. We have determined the composition of the growing amorphous phase at the Zr interface in these Ni-Zr diffusion couples to be 55 ± 4% Zr. We investigated the kinetics of solid state reactions competing with the solid state amorphization reaction and found the value of the activation energy of the initial crystallization and growth of the growing amorphous phase to be 2.0 ± 0.1 eV, establishing an upper limit on the thermal stability of the growing amorphous phase.

High resolution studies of the solid state amorphization reaction in the ZrCo system with the atom probe/field ion microscope

1994 ◽  
Vol 343 ◽  
Author(s):  
Susanne Schneider ◽  
Ralf Busch ◽  
Konrad Samwer
Keyword(s):  
Solid State ◽  
Single Crystal ◽  
Grain Boundaries ◽  
Amorphous Phase ◽  
Rutherford Backscattering Spectrometry ◽  
Atom Probe ◽  
Nanometer Scale ◽  
Probe Field ◽  
Field Ion Microscope ◽  
State Amorphization

ABSTRACTThe atom probe/field ion microscope is introduced as a new powerful investigation device to study the early stages of the solid state amorphization reaction (SSAR). A bilayer of Zr and Co was condensed under UHV conditions on W wire tips and analyzed in a field ion microscope (FIM) combined with an atom probe (AP). The reaction of Co with Zr has been studied at room temperature. FIM pictures and AP analysis have shown that even at low temperatures an amorphous phase is formed at the Zr/Co interface and in the Zr grain boundaries. In these areas concentration profiles have been taken on a nanometer scale. Most likely, the extended solid solution of Co found in α- Zr grain boundaries causes the formation of the amorphous phase. Further, Rutherford backscattering spectrometry (RBS) suggests that even point defects and dislocations at the surface of an α- Zr single crystal are sufficient to initiate the SSAR between a polycrystalline Co layer vapour- deposited onto that single crystal.

scholarly journals Generalized Melting Criterion for Amorphization

1992 ◽  
Vol 291 ◽  
Author(s):  
R. Devanathan ◽  
N. Q. Lam ◽  
P. R. Okamoto ◽  
M. Meshii
Keyword(s):  
Solid State ◽  
Strong Support ◽  
Atomic Displacement ◽  
Mean Square ◽  
Root Mean Square Amplitude ◽  
Embedded Atom ◽  
Average Shear ◽  
Lindemann Criterion ◽  
Dynamics Simulations ◽  
State Amorphization

ABSTRACTWe present a thermodynamic model of solid-state amorphization based on a generalization of the well-known Lindemann criterion. The original Lindemann criterion proposes that melting occurs when the root-mean-square amplitude of thermal displacement exceeds a critical value. This criterion can be generalized to include solid-state amorphization by taking into account the static displacements. In an effort to verify the generalized melting criterion, we have performed molecular dynamics simulations of radiation-induced amorphization in NiZr, NiZr2, NiTi and FeTi using embedded-atom potentials. The average shear elastic constant G was calculated as a function of the total mean-square atomic displacement following random atom-exchanges and introduction of Frenkel pairs. Our results provide strong support for the generalized melting criterion.

Amorphous-phase formation and initial reactions at Pt/GaAs interfaces

1991 ◽  
Vol 49 ◽  
pp. 858-859
Author(s):  
Dae-Hong Ko ◽  
Robert Sinclair
Keyword(s):  
Solid State ◽  
Amorphous Phase ◽  
Phase Formation ◽  
Compound Semiconductor ◽  
Metal Compound ◽  
Heat Of Mixing ◽  
Semiconductor Interface ◽  
Direct Demonstration ◽  
State Amorphization ◽  
Amorphous Phase Formation

It is now well known that many metals form a l-2nm amorphous interdiffused layer when deposited onto clean Si surface, which grows upon annealing in some systems but crystallizes into stable, or metastable, phases in others. Such behavior can be interpreted in terms of a solid-state amorphization, driven by a negative heat of mixing of the elements with the amorphous phase produced for kinetic reasons. Some metal/compound semiconductor systems also show the same reaction behavior. Though there have been some reports, using electron diffraction, on the amorphous phase formation at metal-compound semiconductor interface upon low temperature annealing, because the expected thickness might only be several atomic layers, it is clear that high resolution transmission electron microscopy (HRTEM) is the most powerful technique to study such a phase. This article reports on the amorphous phase formation and the initial stages of reaction occuring at Pt/GaAs interfaces upon annealing with HRTEM, and this is the most direct demonstration of solid state amorphization of a metal with a compound semiconductor.

scholarly journals Interdependence of stress and interdiffusion during solid-state amorphization in Ni–Hf

2000 ◽  
Vol 15 (2) ◽  
pp. 463-475 ◽  
Author(s):  
W. S. L. Boyer ◽  
M. Atzmon
Keyword(s):  
Solid State ◽  
Tensile Stress ◽  
Diffusion Couple ◽  
Amorphous Phase ◽  
Ion Irradiation ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Curvature Measurements ◽  
Stress Variations ◽  
State Amorphization

The evolution of stress in a Ni–Hf diffusion couple during solid-state amorphization reaction has been monitored by substrate curvature measurements and x-ray diffraction. The latter technique allowed an independent determination of the contribution of changes in stress-free lattice parameter to the stress in the crystalline layers. The results indicate that the amorphous phase forms under a large tensile stress, which relaxes as the reaction progresses. This stress in the amorphous phase is consistent with the volume change associated with the reaction. Stresses in the crystalline, elemental phases are considerably smaller and not affected by the reaction. Low-temperature Ni ion irradiation increases the tensile stress in the diffusion couple. The large observed stress variations are not accompanied by variations in the effective interdiffusion coefficient.

Formation and growth of an amorphous phase by solid-state reaction between GaAs and Co thin films

1991 ◽  
Vol 6 (7) ◽  
pp. 1532-1541 ◽  
Author(s):  
F-Y. Shiau ◽  
S-L. Chen ◽  
M. Loomans ◽  
Y.A. Chang
Keyword(s):  
Thin Films ◽  
Solid State ◽  
Amorphous Phase ◽  
Solid Solution Phase ◽  
Pseudobinary System ◽  
Transmission Electron ◽  
Gaas Structure ◽  
Thermodynamic Driving Force ◽  
Stability Data ◽  
State Amorphization

Solid-state amorphization reaction (SSAR) between GaAs and Co thin films was investigated by transmission electron microscopy and Auger electron spectroscopy. Upon annealing of GaAs/Co thin-film couples at 260–300 °C, an amorphous phase was observed to form. Annealing at higher temperatures or for longer times led to the crystallization of the amorphous phase into a supersaturated CoAs solid solution phase with the B31 structure. Amorphization is attributed to the rapid diffusion of Co in the rather open GaAs structure. In order to consider the thermodynamic driving force for amorphization and subsequent crystallization, the phase diagram of CoGa–CoAs was investigated using DTA and metallography. The pseudobinary system was modeled thermodynamically to yield relative stability data for the various phases between GaAs and Co. These data were used to rationalize the amorphization process.

Solid-state amorphization reaction by temperature-dependent ion mixing

1989 ◽  
Vol 4 (6) ◽  
pp. 1299-1302 ◽  
Author(s):  
E. Ma ◽  
C. W. Nieh ◽  
M-A. Nicdlet ◽  
W. L. Johnson
Keyword(s):  
Solid State ◽  
Long Range ◽  
Amorphous Phase ◽  
Ion Irradiation ◽  
Al Alloy ◽  
Temperature Dependent ◽  
Compound Formation ◽  
State Amorphization

A layer of amorphous Mo–Al alloy is formed by ion-assisted solid-state interdiffusion reaction of a Mo/Al bilayer. Xe ion irradiation at 200 °C enhances the long-range diffusion of the dominant moving species while the formation of equilibrium compounds remains inhibited. The idea of using the temperature-dependent ion mixing at intermediate temperatures to promote a solid-state amorphization reaction opens the possibility of growing an amorphous phase in a system where both compound formation and interdiffusion are difficult

Thermodynamic Analysis for the Solid-State Amorphization and Subsequent Crystallization of GaAs/Co

1991 ◽  
Vol 230 ◽  
Author(s):  
F.-Y. Shiau ◽  
S.-L. Chen ◽  
M. Loomans ◽  
Y. A. Chang
Keyword(s):  
Phase Diagram ◽  
Solid State ◽  
Liquid Phase ◽  
Gibbs Energy ◽  
Phase Equilibria ◽  
Amorphous Phase ◽  
Thermodynamic Analysis ◽  
Supercooled Liquid ◽  
State Amorphization

AbstractPhase equilibria along the CoGa-CoAs join were determined by DTA and metallography. On the basis of these data and the phase diagram of Co-Ga-As at 600 °C, thermodynamic values for the various phases along the GaAs-Co join were estimated. The Gibbs energy of the amorphous phase is approximated to be that of the supercooled liquid phase. These data were used to rationalize the amorphization process.

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