Microstructure formation and control in additive manufacturing of metallic alloys

金属合金的增材制造（AM）作为减材制造的可行替代方案迅速出现。金属部件的微观结构是弹性和可靠使用的关键因素，具有预期的机械性能。然而，在AM快速凝固过程中，熔池生长界面附近的局部温度场严重影响了微观组织的形成。在金属AM过程中发生的典型热条件往往会促进强晶粒取向和织构;而等轴显微组织由于其机械性能和弹性而在广泛的工程应用中最受欢迎。本博士项目旨在研究可应用于AM过程的可能的显微组织控制机制，以迈向未来的在线过程控制能力。潜在的强化形核机制，可以作为控制措施，以减少取向晶粒结构和纹理的目的是检查。特别是，可以控制熔池流动的方式作为增加成核/碎裂潜力的工具，同时降低熔池处的有效热梯度的方式将是关键焦点之一。在实验上，先进的同步辐射成像技术将被用来研究移动熔池的演变和固液界面处的微观结构发展之间的联系。此外，非原位后金相检查与支持性计算框架，预计将开发解释和综合实验数据到全面的科学和工程信息。

Additive manufacturing (AM) of metallic alloys is rapidly emerged as a viable alternative to subtractive manufacturing. Microstructures of metallic components are a key contributory factor for resilience and reliable use with intended mechanical properties. The microstructure formation during rapid solidification of AM is however severely affected by the local temperature field near the growth interface of the melt pool. The typical thermal conditions occur during metal AM tend to promote strong grain orientations and texture; instead equiaxed microstructures are mostly preferred for wide range of engineering applications for their mechanical properties and resilience.This PhD project aims to study possible microstructure control mechanisms that can be applied to AM processes, in order to step towards the future inline process control capabilities. Potential for intensified nucleation mechanisms, which can act as control measures to reduce oriented grain structures and textures are aimed to examine. In particularly, the ways that can control the melt pool flow as tool to increased nucleation/fragmentation potential with ways to reduce effective thermal gradients at the melt pools will be one of the key focuses. Experimentally, advanced synchrotron imaging techniques will be employed to investigate the links between the evolution of the moving melt pool and the microstructure development at the solid-liquid interface. In addition, ex situ post metallographic examinations with a supportive computational framework is expected to develop to interpret and integrate experimental data into comprehensive scientific and engineering information.