Abstract
Various melting-related phenomena (like surface melting, size dependence of melting temperature, melting of few nm-size particles and overheating at a very fast heating rate) are of great fundamental and applied interest, although the corresponding theory is still lacking. Here we develop an advanced phase-field theory of melting coupled to mechanics, which resolves numerous existing contradictions and allowed us to reveal exciting features of melting problems. The necessity of introducing an unexpected concept, namely, coherent solid-melt interface with uniaxial transformation strain, is demonstrated. A crossover in temperature dependence of interface energy for radii below 20 nm is found. Surface-induced premelting and barrierless melt nucleation for nanoparticles down to 1 nm radius is studied, and the importance of advanced mechanics is demonstrated. Our model describes well experimental data on the width of the molten layer versus temperature for the Al plane surface and on melting temperature versus particle radius.
Highlights
Various melting-related phenomena are of great fundamental and applied interest, the corresponding theory is still lacking
There are important molecular dynamics (MD) studies[5,6,10], we focus on the continuum phase-field approach (PFA), which allows consideration of larger spatial and time scales and operates explicitly with thermodynamic and kinetic parameters determined at the macroscale
Solids and liquids are described in completely different continuum mechanical frameworks, which sophisticates the description of intermediate state
Summary
Various melting-related phenomena (like surface melting, size dependence of melting temperature, melting of few nm-size particles and overheating at a very fast heating rate) are of great fundamental and applied interest, the corresponding theory is still lacking. Numerous melting-related phenomena represent fundamental material problems and are currently under intense experimental and theoretical study They include surface premelting and melting below the thermodynamic melting temperature θe, caused by reduction in surface energy and leading to appearance of a molten, nanometer-thick layer[1,2]; reduction in melting temperature θm with reduction of the particle radius R down to nanoscale[3,4]; melting of particles with radii comparable to and smaller than the equilibrium solid–liquid interface width δe, which is a few nm[3,5]; and overheating above θe during very fast heating[6,7]. Interface energy varies in a non-trivial way for ri≤4δe 12 nm with decreasing ri, increasing for θ > θe and decreasing for θ < θe; this is opposite to the behaviour for ri > 12 nm
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