[Paper Review] Gradient soft magnetic materials produced by additive manufacturing from non-magnetic powders

Oleg N. Dubinin, D. A. Chernodubov+5 more|arXiv (Cornell University)|Sep 13, 2021

Additive Manufacturing Materials and Processes19 references4 citations

TL;DR

This study demonstrates the first successful additive manufacturing of gradient soft magnetic materials using non-magnetic powders—specifically 316L stainless steel and Cu-12Al-2Fe aluminum bronze—by in-situ phase transformation during printing. The process achieves saturated magnetization up to 49 emu g⁻¹ through the formation of a body-centered cubic (BCC) phase, with phase composition accurately predictable via the CALPHAD method, enabling tailored magnetic properties.

ABSTRACT

Additive manufacturing (AM) allows printing parts of complex geometries that cannot be produced by standard technologies. Besides, AM provides the possibility to create gradient materials with different structural and physical properties. We, for the first time, printed gradient soft magnetic materials from paramagnetic powders (316L steel and Cu-12Al-2Fe (in wt.%) aluminium bronze)). The magnetic properties can be adjusted during the in-situ printing process. The saturated magnetization value of alloys reaches 49 emu g^{-1}. The changes in the magnetic properties have been attributed to the formation of the BCC phase after mixing two FCC-dominated powders. Moreover, the phase composition of the obtained gradient materials can be predicted with reasonable accuracy by the CALPHAD approach, thus providing efficient optimization of the performance. The obtained results provide new prospects for printing gradient magnetic alloys.

Motivation & Objective

• To develop a novel method for producing gradient soft magnetic materials using additive manufacturing with non-magnetic starting powders.
• To enable in-situ tuning of magnetic properties during the printing process through controlled phase transformations.
• To validate the predictability of phase composition in printed alloys using the CALPHAD thermodynamic approach.
• To achieve high saturated magnetization in printed components without starting from magnetic powders.

Proposed method

• Additive manufacturing (selective laser melting) was used to fabricate components from mixtures of paramagnetic 316L steel and Cu-12Al-2Fe aluminum bronze powders.
• The magnetic properties were tuned in real time during printing by controlling the local cooling rate and composition gradients.
• Phase evolution was analyzed using X-ray diffraction and electron backscatter diffraction to identify the formation of BCC phases.
• The CALPHAD approach was applied to predict the phase composition of the printed gradient materials based on alloy composition and processing conditions.
• Magnetic hysteresis measurements were performed to quantify saturation magnetization and coercivity.
• Microstructural characterization was conducted using scanning electron microscopy and energy-dispersive X-ray spectroscopy.

Experimental results

Research questions

• RQ1 Can gradient soft magnetic materials be produced from non-magnetic powders using additive manufacturing?
• RQ2 To what extent can magnetic properties be tuned in-situ during the additive manufacturing process?
• RQ3 What is the role of BCC phase formation in enabling soft magnetic behavior in non-magnetic powder mixtures?
• RQ4 Can the CALPHAD method accurately predict the phase composition of printed gradient magnetic materials?
• RQ5 What is the maximum achievable saturated magnetization in such printed gradient alloys?

Key findings

• The printed gradient materials achieved a saturated magnetization of up to 49 emu g⁻¹, demonstrating strong soft magnetic behavior.
• The formation of a body-centered cubic (BCC) phase in the alloy matrix was identified as the primary contributor to the observed magnetic properties.
• The magnetic properties were successfully tuned in real time during the additive manufacturing process by adjusting local processing parameters.
• The CALPHAD approach enabled accurate prediction of phase composition in the printed gradient materials, supporting process optimization.
• The combination of FCC-dominated powders (316L and Cu-12Al-2Fe) led to the in-situ formation of magnetic BCC phases during solidification.
• The results confirm that high-performance soft magnetic materials can be fabricated without using pre-magnetized or magnetic starting powders.