The Computational Study Of The Strain-induced Premelting Of The Heterogeneous Solid-liquid Interfaces

Heterogeneous solid-liquid interfaces widely used in the advanced manufacturing process of many core industrial products,such as high-quality alloys,chips,common heat dissipation devices and the preparation of renewable energy devices.A detailed understanding of the structure and thermodynamic properties of heterogeneous solidliquid interface is very important to describe many related key physical processes,including nucleation,wetting and spreading,grain growth,grain boundary movement,inclusion transport and so on.With the rapid development of experimental and computational simulation technology,the research on homogeneous solid-liquid interface system has become more and more mature,but the research on heterogeneous solidliquid interface system with sharp changes in chemical properties is still insufficient.So far,the research on heterogeneous solid-liquid interface focuses on the characterization of equilibrium interface under hydrostatic pressure,and rarely considers the influence of solid residual stress on interface structure and thermodynamic properties under non hydrostatic pressure.In order to understand the heterogeneous solid-liquid interface more comprehensively,this thesis takes the heterogeneous solid-liquid interface system of Al-Pb alloy with premelting phase transformation at high temperature as the research object,and explores the structural and thermodynamic changes of heterogeneous solid-liquid interface under strain through phenomenological thermodynamic theory and molecular dynamics simulation experiment.Under the condition of small strain near the melting point temperature of aluminum,atomic simulation is used to predict that the strain-induced premelting phase transition occurs at the heterogeneous solid-liquid interface system.The phenomenological thermodynamic theory of strain-induced premelting phase transition is constructed,and the effectiveness of this thermodynamic theory is verified by large-scale molecular dynamics simulation.The asymmetric and nonlinear variation of the thickness of premelted liquid film under different strain application conditions and undercooling temperature are quantitatively explained.At the same time,the core role of excess stress at the solid-liquid interface in the phase transition of low dimensional structure at the interface is identified.By applying time-dependent longitudinal strain wave,the interfacial premelting phase transition is dynamically correlated with periodic strain.In the study of dynamically modulated premelting phase transition,a novel physical mechanism of thermodynamic driving force and free energy is found and clarified.This study predicts the potential possibility of realizing the precise control of solidification / melting dynamics of single substance in addition to the traditional temperature control technology.In addition,the strain-induced premelting phase transition phenomenon and the prediction of regulating the wetting behavior of metal Pb droplets on Al surface are presented by atomic simulation.We investigate solid-solid phase transformation and migration of interface between ambient and strained crystal of Al using molecular dynamics simulation by means of premelting.In agreement with previous observations both Al(100)and Al(110)exhibit premelting near melting temperature and strain enhance the thickness of melt irrespective to sign.In bicrystal of Al,if one of crystal is subjected to strain then internal stresses completely relax during premelting and additionally provides thermodynamic driving force.This melt recrystallise into ambient crystal in pico seconds.The propagating interface velocity as function of temperature and strain both are quantitatively measured.Two types of interface propagation is observed,for thin interfacial melt(two times of lattice constant or less)interface migration is not continuous it is stick–slip and stochastic,and for thick premelted layer interface migration is barrier less.The results obtained are applicable to many structural changes like grain evolution,twinning,fracture and dislocations,phase transformation such as melting-solidification and solid-solid.Finally,we extend the study of strain-induced premelting phase transformation to the curved interface system,and select the liquid Pb inclusions embedded in the single crystal aluminum matrix.The equilibrium atom simulation technique suitable for liquid inclusions in solid matrix is developed.Irving Kirkwood algorithm is introduced into the calculation of radial local pressure tensor distribution function of confined liquid inclusions,showing a delicate mechanical balance between the internal pressure of inclusions and the interfacial premelting layer and the block matrix,which makes a theoretical breakthrough for the interfacial premelting phase transition of confined droplets and lays the foundation of microphysical images and thermodynamic data.