Recently, tomoscopy (also known as time-resolved tomography) has been used to observe dynamic processes in various materials and systems. It can now capture up to 1000 tomograms per second (tps) for an extended duration of minutes. Focused laser beams can be used for local melting of material for cutting, cladding, or welding parts. This technique can also be used to sinter powder particles for additive manufacturing of components.

Despite its potential, laser-based powder bed fusion (LPBF) parts often contain many pores, limiting their application potential. X-ray tomoscopy can help in analyzing pore formation in detail and improving production parameters. Image superposition which is typical for radiography is no longer an issue, and it allows edge effects of thin samples to be avoided. In a proof-of-concept operando tomoscopic experiment, loose aluminum powder was processed under realistic production conditions with a fiber laser and a fast positioning system for beam guidance by superimposing the movement of the laser on that of the rotating powder bed, the last being necessary for tomography. That way the interaction area could be advanced while simultaneously recording tomograms with a temporal resolution of 100 tps.

The temporal evolution of the aluminum powder particles during the formation of the first molten layer in this simplified LPBF sintering was recorded along two complete circles of 2 mm diameter with a relative laser feed rate of 1 m/min in 0.72 s and the results were analyzed. The experiment showed the formation of balling (caused by low laser energies), denudation zones and porosity. The first circle showed individual melt lumps forming at the position of the laser spot. The lumps had an equivalent diameter of 0.2-0.5 mm and retained their original shape throughout the process until they solidified. X-ray tomoscopy was used to quantify the evolution of the total volume of molten powder and the porosity formed within the particles in the first circle. The total volume of the molten powder increased almost linearly with time, while the majority of pores did not form until the first lumps began to solidify, as residual gases cannot diffuse out fast enough to avoid being trapped. After passing the laser again and melting the lumps again, the porosity was reduced about tenfold.

These findings provide insight into improving production parameters and developing dedicated alloys for additive manufacturing. Overall, this study demonstrates the potential of in-situ operando tomoscopy to advance our understanding of laser interaction and ultimately improve the quality of additively manufactured parts.