Microstructure formation and control in additive manufacturing of metallic alloys

金属合金的加法制造(AM)是减法制造的一种可行的替代方法。金属部件的微观结构是具有预期机械性能的弹性和可靠使用的关键因素。然而，AM快速凝固过程中微观组织的形成受到熔池生长界面附近局部温度场的严重影响。在金属AM过程中出现的典型热条件往往促进强烈的晶粒取向和织构；相反，等轴组织因其机械性能和回弹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工艺的可能的微观组织控制机制，以迈向未来的在线过程控制能力。强化形核机制的可能性，这可以作为控制措施，以减少定向晶粒组织和织构的目的是审查。特别是，如何控制熔池流动以提高成核/破碎势，同时降低熔池的有效温度梯度，将是研究的重点之一。在实验上，将使用先进的同步辐射成像技术来研究移动熔池的演化与固-液界面微观结构发展之间的联系。此外，预计将发展具有支持性计算框架的非原位金相检查，以解释实验数据并将其整合为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.