A Research on Microscopic and Macroscopic Mechanics in Melting/Solidification Processes Incorporating Moving Boundary/Interface, and Its Application to Welding and Bonding

从微观、宏观和细观三个角度对熔化和凝固过程进行了分析，以揭示熔化和凝固过程的机理，并建立了焊接、连接等包含运动边界和界面的相变过程的热力学理论。微观方法采用分子动力学方法，宏观方法采用有限元方法，介观分析采用相场法和晶体塑性理论。(1)分子动力学微观分析方法：分析了原子在固液界面附近的运动，评价了界面的稳定性以及界面能量随晶体取向变化的各向异性。根据取向与界面能的关系确定晶体生长的择优取向。(2)焊接热影响区的力学性能：微观…中的变形用微网格法测量了Mo.9Cr-1Mo钢焊缝金属、热影响区和母材中更多的观察区域，揭示了硬度、组织变化和应变之间的关系。(3)相场法晶体生长过程分析：采用相场法分析晶体生长过程，引入力学和热物理性质以及基于分子动力学模拟的各向异性。通过这些参数的组合，得到了不同模式的树枝晶。(4)基于晶体塑性理论的有限元分析：用有限元方法模拟了热影响区的变形行为，通过引入晶粒度和各向异性的模型得到的结果与实验结果吻合较好。这些结果支持了(2)中的关系。较少

Analyses on melting and solidification processes are carried out by microscopic, macroscopic and mesoscopic viewpoints, in order to reveal the mechanism and to build up thermo-mechanical theory on the phase transformation processes incorporating moving boundary and interface, such as welding and joining. Molecular dynamics method and the finite element method are used as microscopic and macroscopic method, respectively, while phase-field method and crystal plasticity theory are applied to mesoscopic analysis. The summary is as follows :(1) Microscopic Analysis by Molecular Dynamics Method : The motions of atoms around the interface of solid and liquid are analyzed and the stability of the interface, anisotropy in the interface energy depending on crystal orientation are evaluated. And the preferred orientations of crystal growth are determined from the relation between the orientation and interface energy.(2) Mechanical Properties of Welded Heat Affected Zone : Deformation in the micro … More scopic area in the weld metal, heat-affected zone, and parent material of Mo.9Cr-1Mo steel is measured by the micro-grid method, and the relation between hardness, structural change and strain is revealed to be clear.(3) Analysis of Crystal Growth Process by Phase-Field Method : Crystal growth process is analyzed by the phase-field method in which mechanical and thermophysical properties and anisotropy based on the molecular dynamics simulation are introduced. Various modes of dendritic crystals are obtained by the combination of the parameters. These results made it possible to observe the dynamic process of the pattern formation, and some phenomena such as initial stage of crystal growth, which is difficult to experimentally observe, are demonstrated.(4) Finite Element Analysis Based on Crystal Plasticity Theory : Deformation behavior in the heat-affected zone was simulated by the finite element method, and the results obtained by the model in which grain size and anisotropy was introduced were revealed to be corresponding to experimental results. These results are supporting the relation obtained in (2). Less