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、宏观和细观的角度对熔化和凝固过程进行分析，以揭示熔化和凝固过程的机理，建立焊接和连接等含运动边界和界面的相变过程的热力学理论。细观分析采用分子动力学方法，宏观分析采用有限元方法，细观分析采用相场法和晶体塑性理论。（1）分子动力学方法的微观分析：分析了固液界面附近原子的运动，评价了界面的稳定性，界面能随晶体取向的各向异性。根据晶体生长的择优取向与界面能的关系，确定了晶体生长的择优取向。(2)焊接热影响区的力学性能：微观变形 关于我们 采用微网格法对Mo.9Cr-1 Mo钢焊缝金属、热影响区和母材的显微区进行了测量，揭示了硬度、组织变化与应变之间的关系。(3)晶体生长过程的相场法分析：采用相场法分析晶体生长过程，引入基于分子动力学模拟的晶体力学、热物理性质和各向异性。通过这些参数的组合，得到了不同形态的枝晶。这些结果使得观察图形形成的动态过程成为可能，并证明了一些现象，如晶体生长的初始阶段，这是很难实验观察。(4)基于晶体塑性理论的有限元分析：通过有限元法模拟了热影响区的变形行为，结果表明，引入晶粒尺寸和各向异性的模型得到的结果与实验结果一致。这些结果支持了（2）中得到的关系式。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