Simultaneous high-speed ultrasound and synchrotron x-ray imaging for monitoring melt pool dynamics in metallic additive manufacturing

Abstract

Fundamental to metallic additive manufacturing (AM) is the laser-powder-substrate interaction that leads to localized melting of metallic powder to a previously solidified substrate. The formation of the melt pool and the subsequent solidification dictate the resultant microstructures and properties of the processed materials, which then influence both part quality and performance. Open ended questions involving the optimization of process parameters for defect free and high performing parts remain at the heart of AM science. Further understanding of melt pool and solidification behavior is required to help answer these questions. In this presentation, 25 MHz ultrasonic shear waves are used to probe dynamic melt pool behavior in Al6061 by observing the scattering from the solid/liquid and liquid/gas boundaries. High-speed synchrotron x-ray imaging was employed simultaneously with the ultrasonic measurement for validation. Melt pool features observed in the x-ray images were then associated with features in the synced ultrasound measurement. Specifically, the scattered response tracked with the depth of the melt pool. Finite element models depicting wave-scattering were also used to predict wave scattering and help interpret the ultrasonic response. These preliminary results provide support for ultrasonic scattering as a promising method to evaluate melt pool behavior in metallic additive manufacturing processes.