KU Leuven Team Manipulates Metal Microstructure During 3D Printing

A research team at KU Leuven has achieved a significant advancement in metal additive manufacturing by demonstrating the ability to influence a part's microstructure locally during the printing process itself. This development bypasses the need for post-build heat treatments, a long-standing goal for the industry.

While laser powder bed fusion (LPBF) has excelled in producing complex geometries, controlling the material properties within those shapes has been a greater challenge. Properties like strength, ductility, and fatigue life are determined by microstructure, which is heavily influenced by the thermal history during printing. Traditionally, this thermal history has been an accepted outcome rather than a designed parameter.

This challenge is particularly pronounced in super duplex stainless steels, used in demanding applications for their combined strength and corrosion resistance. Their performance relies on a balanced microstructure of ferrite and austenite. However, LPBF's rapid cooling rates typically suppress austenite formation, resulting in a brittle, predominantly ferritic structure. Post-print furnace heat treatment is currently the standard method to achieve the desired microstructure, but it adds cost, time, distortion risk, and provides a uniform microstructure throughout the part.

The KU Leuven team's approach, published in Additive Manufacturing, utilizes a dual-laser LPBF configuration. A second, trailing laser follows the primary melting laser at a controlled offset. This trailing laser reheats the newly solidified material within a specific temperature window (800–1200 °C for super duplex stainless steel), allowing austenite to nucleate and grow from the ferritic structure before it cools further. This in-situ phase transformation achieves the desired microstructure without external heat treatment.