Acoustic detection of phase transformation and crystallization for laser powder-bed fusion

To ensure process stability and reproducibility in laser powder-bed fusion (LPBF), various in-situ and ex-situ monitoring techniques have been developed. Among the in-situ methods, optical and acoustic approaches are the most prominent. A key advantage of acoustic techniques over optical methods is their ability to detect internal part emissions, providing deeper insights into the material behavior. In this work, we show examples of LPBF processing conditions in which acoustic emission indicated changes in microstructure. These include the occurrence of martensitic transformations in Ti-6Al-4V, and the formation of crystalline phases in Bulk Metallic Glasses (BMGs). To help in the interpretation of the acoustic signals, ground truth data was extracted from operando synchrotron X-ray diffraction experiments, and from Finite Element (FEM) thermal simulations.