title: Unconventional Alloy Design of (Nd, Pr)-Fe-B Based Alloys for the Production of Permanent Magnets by Additive Manufacturing
Creators: name: Schäfer, Lukas
Publisher: name: UNSPECIFIED
Year: 2023

description: The scientific goal of this work is to investigate hard magnetic alloys based on Nd Fe B for the production of permanent magnets by additive manufacturing. The experimental work covers the material chain from the element to the (printed) component, including the synthesis of the alloys from elements, the thermal treatments necessary to improve microstructure and magnetic properties and finally the powder production and laser fusion to obtain bulk samples. By this, an interdisciplinary approach with modern characterization techniques of materials science and novel manufacturing techniques is chosen, focusing on the qualification of hard magnetic rare earth alloys for the production of permanent magnets by laser powder bed fusion (PBF-LB). The chosen compounds are related to the commercial high-performance Nd Fe B magnets. However, due to the very local and complex melting and solidification processes during PBF LB, the materials need to be adapted. In this context, two approaches were investigated which have in common the formation of unusual phases and microstructures in the Nd-Fe-B system. First, the influence on phase formation and magnetic properties of element dopants such as cobalt, copper and transition metals (titanium, vanadium, zirconium, molybdenum, niobium, tungsten, tantalum) were investigated by the synthesis of alloys with systematic addition of the dopants. The solidification behavior was investigated by rapid solidification experiments which provides metastable phases/ microstructure and is starting point for the magnetic hardening by thermal treatments. A coercivity of almost µ0HC = 1 T could be achieved in Nd16Fe53Co20Cu2Mo2B7 samples. A second approach was based on high copper addition in (Pr,Nd) Fe Cu B compounds which is the basis for high coercivity. Uncommon intermetallic phases are forming whose influence on coercivity was investigated. For this purpose, the phase stability and magnetic properties were explored within a quasi-ternary phase diagram. With suitable alloy adjustment and heat treatment, coercivities above µ0HC = 2 T could be achieved in Pr Fe Cu alloys. Based on these lab-scale experiments, alloy compositions with promising magnetic properties were selected and powder for the additive manufacturing tests was produced. In this context, a systematic approach and parameter study of the PBF LB experiments was established in cooperation with the Institute for Production Management, Technology and Machine Tools (PTW), adapted to small material quantities and the properties of the materials used here, which differ significantly from structural materials. In addition to the adaptations of the materials and alloy modifications, recurring errors and problems during additive manufacturing process could be identified. In addition to the exceptional microstructures and magnetic properties in the modified rare earth-based alloys, the findings from the PBF LB experiments serve as a starting point for future investigations with advanced process monitoring methods.