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Development and characterisation of soft magnetic iron-silicon alloys for laser beam powder bed fusion additive manufacturing
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With the constant increase of global warming and the electric transition in the transportation
industry, improving the efficiency and reducing the power losses of soft magnetic materials is
mandatory. This work investigated the Fe-Si alloys production with the additive manufacturing
technology Powder Bed Fusion - Laser Beam (PBF-LB). This soft magnetic material has many
applications on electric machines. Like all the additive manufacturing techniques, layer-by-layer
productions, the PBF-LB is characterised by melting a layer of powder with a laser beam in the
desired regions, allowing a big design freedom.
The main objective is to produce samples of Fe-3.5Si and Fe-6.5Si with PBF-LB, optimising
the process parameters for each alloy to obtain the highest relative density and less surface roughness. Every built sample is post-processed and prepared for microscopy observation. Several
heat treatments are also applied to understand the effects of the stress relief and grain growth
on the final properties. The final procedure is the measure of magnetic properties, hardness
values and grain size and shape.
The magnetic properties and hardness values measured on Fe-3.5Si alloys indicate a dependence on the production scanning pattern and the posterior heat treatment applied in the
samples. Samples with higher relative densities and less surface roughness are observed to reach
higher magnetic permeabilities and inductions, and smaller coercivities, leading to fewer hysteresis losses. After a recrystallisation annealing heat treatment, the samples have improved their
overall magnetic properties. It is observed that the hardness of the samples decreases with the
heat treatments. The Fe-6.5Si alloys reach better magnetic properties than the previous alloy,
being crack susceptible due to the formation of ordered phases. It is concluded that Fe-Si alloys produced with additive manufacturing achieve good results, but these materials could have
even better magnetic properties (fewer losses and higher efficiencies) by removing the cracks and
controlling the microstructure orientation. The changes in the production process or chemical
composition of high silicon alloys can help reduce the cracking and reach denser samples.
Descrição
Tese de Mestrado, Engenharia Física, 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Fabrico Aditivo Fusão em camada de pó com feixe laser Materiais magnéticos macios Ligas de ferro silício Propriedades magnéticas Teses de mestrado - 2023