Collaborative Research: Understanding Ultrasonic Effects in Laser Additive Manufacturing via in situ Synchrotron Imaging and Diffraction Analysis

While laser based additive manufacturing (AM) offers significant advantages for fabricating intricately shaped metallic components, high incidence of undesired microstructural features and defects remain barriers to a wider industrial adoption of this process. A few recent studies have investigated an approach, referred to as ultrasonically assisted (UA)-AM, that is based on superimposing ultrasonic vibration during laser AM for suppressing defects and refining microstructure. However, the fundamental mechanisms of the UA-AM process are not completely understood, and the current models ignore the transient nature and far-from-equilibrium conditions of the process. This project will utilize synchrotron imaging and diffraction with high space and time resolutions to observe the core mechanisms of the UA-AM process. The knowledge derived from this research intends to benefit AM industries and facilitate effective and innovative incorporation of UA into various manufacturing processes that involve rapid melting and solidification. The project looks to contribute to multidisciplinary workforce training and promote STEM education with an e-Learning module and hands-on activities for K-12 students. To observe the underlying physics of UA including the melt dynamics and microstructure evolution, this project seeks to develop an innovative UA laser melting system that fits into the advanced synchrotron radiation facilities. UA effects on the AM process will be analyzed through in situ synchrotron imaging and diffraction analysis, followed by postmortem characterization and integrated multi-scale, multi-physics modeling. In situ imaging will target: (1) melt geometry overview (2) melt flow dynamics (3) dendritic microstructure growth and interactions. Diffraction analysis will focus on melt interior and heat affected zone to determine the phase transformation, thermal history, and stress development. Also, residual stress distribution will be measured with ex situ diffraction analysis. A computational fluid dynamics model coupling the acoustic field will be developed to determine the spatial distribution and temporal evolution of temperature, velocity and pressure fields. These physical fields will serve as input for the phase field modeling of alloy solidification, looking to fully reveal UA effects on the thermo-mechanical-chemical fields and microstructure evolution during laser-based AM processes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.