激光增材制造中金属熔池固液耦合机制及材料热力本构关系

There is transmission of energy, momentum and mass in laser molten pool, which would affect the parameters of precision, deformation and crack in laser additive manufacturing. In order to study materials photothermal radiation, the relationship with wavelength, temperature,emissivity would be analyzed by grating spectrum technology.The heat transmission model woud be set up to research the relationship between laser molten pool temperature and its heat exchange, convection and mass exchange. The deformation law and material dynamic constitutive relations in different directions will be investigated in SHPB experiments. Mechanism of material distortion, crack nucleation, growth effect and thermal shock on the development of material damage can be developed by the relationship between stress and strain. Theoretical breakthroughs are expected to be achieved in materials photothermal radiation and thermal-mechanical coupling constitutive model. Based on the established elasto-plastic constitutive relations with damage, damage evolution equation and crack criterion, the theoretical thermal-mechanical coupling constitutive model will be constituted. Some new phenomena and mechanism on photothermal radiant laws and structure deformation damage will be achieved by studying the stress-strain effect and crack formation and evolutionary mechanisms of component material in laser additive manufacturing.

激光增材制造过程中金属熔池存在能量、动量和质量传输物理行为，直接影响零件精度、变形与裂纹。 通过激光与材料相互作用研究，分析材料光热辐射数理模型，通过光栅光谱实验检测，研究其随波长、温度、发射率等变化规律，建立熔池传热数学物理模型，分析熔池表面温度与内外传热、传质、对流关系。 开展SHPB实验，建立材料应力应变曲线，构建其动态本构关系，分析激光增材制造零件变形机制及其动态力学行为，为零件材料及工艺选择提供依据；分析零件裂纹形成、成核与长大效应，探讨热冲击对损伤发展的影响机理。 有望在材料光热辐射与材料热力耦合本构关系方面取得理论突破，研制出激光增材制造材料光热辐射检测系统，建立基于SHPB实验的激光增材制造材料本构测试与分析方法，建立材料应力应变曲线和裂纹分类数据库，探索激光增材制造中光热辐射规律和结构变形破坏的新现象和新机理。

针对送粉式金属激光增材制造的光热辐射现象，研制激光熔池高速检测系统并进行高温标定，每秒200帧图像采集数据表明，熔池中心区域淡淡的暗区迅速长大并流向熔池边缘，表明高斯分布激光熔池对流主要从中间往上并快速往边缘进行，熔池内熔渣从中心涌出，迅速汇合长大并被熔体的快速流动带向熔池边；采用手持式光谱仪与激光增材机器人系统集成，实验检测不同工艺条件下熔池光热辐射，表明不同基材与粉末条件下，会形成两个主峰，光谱曲线与横坐标构建的区域积分面积随激光功率增长呈现明显的线性关系。开展全氩气环境下TC4合金激光增材实验，建立其本构模型，采用SHPB实验建立TC4应力-应变间对应关系，在NaCl和H2SO4中的耐腐蚀性均比基体强，在高应变率下具有明显应变率强化、增塑及软化效应，平行和垂直于沉积方向上屈服强度均高于普通TC4合金。开展了不同陶瓷材料及碳纤维增强增材涂层实验，重点分析其微观组织规律及裂纹形成及演变规律。在前述研究基础上，重点针对核聚变领域耐高温及辐射屏蔽重大需求，用纯钨粉开展低活化钢表面激光增材实验，构建钨涂层本构模型，对钨涂层热性能、微观组织、物相组成及裂纹形成机制等进行研究，有望为核聚变第一壁材料制备提供新的方法与数据参考。