Researchers at IMDEA Materials have published a study examining how crystallization occurs in Finemet alloys produced via laser powder bed fusion (LPBF), offering new insight into how process parameters shape the microstructure of soft-magnetic components made from metallic glasses.

Metallic glasses, also known as amorphous metals, are valued for their combination of mechanical strength, corrosion resistance and magnetic performance. Finemet alloys in particular are attractive for energy-related applications including transformers, inductors and electric motors. Broader adoption of these materials has, however, been limited by the difficulty of producing bulk components with complex geometries while preserving their amorphous or nanocrystalline structure.

LPBF presents an alternative to conventional manufacturing techniques, but the extreme thermal conditions inherent to the process can induce crystallization of Finemet’s iron-silicon (Fe-Si) microstructure — a factor that directly affects the final component’s magnetic efficiency, electrical resistivity, and mechanical behavior.

Double scanning strategy

IMDEA Materials study maps crystallisation behaviour in LPBF-processed Finemet alloys

Published in Additive Manufacturing and carried out under the Horizon Europe AM2SoftMag project, the study used a double scanning strategy with variable scan speeds to tailor thermal conditions during printing and analyze their effect on the resulting microstructure. 

Crystallites formed through this process were found to be significantly larger and more heterogeneous than those produced through conventional routes such as the annealing of melt-spun ribbons, with size variation ranging from a few tens to several hundred nanometres.

Crystallization was shown to occur either during rapid solidification of the melt pool under specific cooling conditions, or in the heat-affected zone (HAZ) during subsequent laser passes. Researchers also identified a smaller population of dendritic crystals forming at the boundaries of the melt pool, with their size decreasing as cooling rates increased.

Parameter selection and process implications

“What this work shows is that to manufacture a nanocrystalline-amorphous composite with a complex geometry using LPBF, and which is suitable to be used as a passive motor component, the selection of parameters should aim to lower cooling rates,” said Saumya Sadanand, Lead Author and researcher at IMDEA Materials.

“This serves to increase the nucleation rate, suppressing the formation of large grains and limiting the formation of nanocrystals to the HAZ.

“Understanding these crystallization mechanisms is crucial to the stability and performance of metallic glasses, and thus to expand their practical applications and integrate them into complex, high-performance systems.

“Overall, these findings highlight the strong influence of thermal gradients and cooling dynamics on nucleation and growth mechanisms.”

The research was conducted by IMDEA Materials’ Sustainable Metallurgy group under Professor. Teresa Pérez Prado, with contributions from Dr. Biaobiao Yang and Dr. Marcos Rodríguez Sánchez, in collaboration with Saarland University, the University Rey Juan Carlos and the Technical University of Berlin.