Dislocation-mediated melting: The one-component plasma limit (original) (raw)
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Melting as a dislocation-mediated phase transition
Physical Review B, 2000
We present a theory of the melting of elemental solids as a dislocation-mediated phase transition. We model dislocations near melt as non-interacting closed strings on a lattice. In this framework we derive simple expressions for the melting temperature and latent heat of fusion that depend on the dislocation density at melt. We use experimental data for more than half the elements in the Periodic determine the dislocation density from both relations. Melting temperatures yield a dislocation density of (0.61 ± 0.20) b −2 , in good agreement with the density obtained from latent heats, (0.66 ± 0.11) b −2 , where b is the length of the smallest perfect-dislocation Burgers vector. Melting corresponds to the situation where, on average, half of the atoms are within a dislocation core.
Analysis of Dislocation Mechanism for Melting of Elements
2000
The melting of elemental solids is modelled as a dislocation-mediated transition on a lattice. Statistical mechanics of linear defects is used to obtain a new relation between melting temperature, crystal structure, atomic volume, and shear modulus that is accurate to 17% for at least half of the Periodic Table.
Analysis of dislocation mechanism for melting of elements: Pressure dependence
Journal of Applied Physics, 2000
In the framework of melting as a dislocation-mediated phase transition we derive an equation for the pressure dependence of the melting temperatures of the elements valid up to pressures of order their ambient bulk moduli. Melting curves are calculated for Al, Mg, Ni, Pb, the iron group (Fe, Ru, Os), the chromium group (Cr, Mo, W), the copper group (Cu, Ag, Au), noble gases (Ne, Ar, Kr, Xe, Rn), and six actinides (Am, Cm, Np, Pa, Th, U). These calculated melting curves are in good agreement with existing data. We also discuss the apparent equivalence of our melting relation and the Lindemann criterion, and the lack of the rigorous proof of their equivalence. We show that the would-be mathematical equivalence of both formulas must manifest itself in a new relation between the Grüneisen constant, bulk and shear moduli, and the pressure derivative of the shear modulus.
Journal of Nuclear Materials, 2017
Materials developed with special surface architecture are shown here to be more resilient to the transient thermomechanical environments imposed by intermittent exposures to high heat flux thermal loading typical of long-pulse plasma transients. In part 1 of this article, we present experimental results that show the relaxation of residual thermal stresses in micro-engineered W surfaces. A dislocation-based model is extended within the framework of large deformation crystal plasticity. The model is applied to the deformation of single crystals, polycrystals, and micro-engineered surfaces composed of a uniform density of micro-pillars. The model is utilized to design tapered surface micro-pillar architecture, composed of a Re core and W coatings. Residual stresses generated by cyclic thermomechanical loading of these architectures show that the surface can be in a compressive stress state, following a short shakedown plasma exposure, thus mitigating surface fracture.
Physical Review Letters, 2003
The microscopic mechanism of the melting of a crystal is analyzed by the constant pressure Monte Carlo simulation of a Lennard-Jones fcc system. Beyond a temperature of the order of 0.8 of the melting temperature, we found that the relevant excitations are lines of defects. Each of these lines has the structure of a random walk of various lengths on an fcc defect lattice. We identify these lines with the dislocation ones proposed in recent phenomenological theories of melting. Near melting we find the appearance of long lines that cross the whole system. We suggest that these long lines are the precursor of the melting process.
Melting at dislocations and grain boundaries: A phase field crystal study
Physical Review B, 2008
Dislocation and grain-boundary melting are studied in three dimensions using the phase field crystal method. Isolated dislocations are found to melt radially outward from their core, as the localized excess elastic energy drives a power-law divergence in the melt radius. Dislocations within low angle to intermediate angle grain boundaries melt similarly until an angle-dependent first-order wetting transition occurs when neighboring melted regions coalesce. High angle boundaries are treated within a screening approximation, and issues related to ensembles, metastability, and grain size are discussed.
Shear Melting of a Hexagonal Columnar Crystal by Proliferation of Dislocations
Physical Review Letters, 2004
A hexagonal columnar crystal undergoes a shear-melting transition above a critical shear rate or stress. We combine the analysis of the shear-thinning regime below the melting with that of synchrotron X-ray scattering data under shear and propose the melting to be due to a proliferation of dislocations, whose density is determined by both techniques to vary as a power law of the shear rate with a 2/3 exponent, as expected for a creep model of crystalline solids. Moreover, our data suggest the existence under shear of a line hexatic phase, between the columnar crystal and the liquid phase.
Melting as a String-Mediated Phase Transition
Phys Rev B, 2000
We present a theory of the melting of elemental solids as a dislocation-mediated phase transition. We model dislocations near melt as non-interacting closed strings on a lattice. In this framework we derive simple expressions for the melting temperature and latent heat of fusion that depend on the dislocation density at melt. We use experimental data for more than half the elements in the Periodic Table to determine the dislocation density from both relations. Melting temperatures yield a dislocation density of (0.61\pm 0.20) b^{-2}, in good agreement with the density obtained from latent heats, (0.66\pm 0.11) b^{-2}, where b is the length of the smallest perfect-dislocation Burgers vector. Melting corresponds to the situation where, on average, half of the atoms are within a dislocation core.
Cooperative Dislocation Generation at Finite Temperatures in Loaded Solids
Journal of the Society of Materials Science, Japan, 1999
This paper describes a theoretical model and a Monte Carlo simulation of cooperative dislocation generation in loaded crystals at finite temperatures. The theoretical work, employing a meanfield approach, is presented for the three-dimensional case when dislocation loops are formed. It describes how extensive plasticity can be initiated in dislocation-free crystals above a critical temperature due to 'homogeneous' cooperative nucleation and expansion of many dislocation loops. The Monte Carlo simulation is carried out to demonstrate the feasibility of the theoretical model. It is performed for a two dimensional case when dislocation dipoles are formed on an underlying lattice under applied loads. The application of this model to the brittle-to-ductile transition and the yielding of whiskers is discussed.