Influence of varying volume energy densities on the magnetic properties of additively manufactured Ni50Fe50

The state of the art of nickel iron alloys specifies that low porosity and large grain sizes are essential to reach sufficient soft magnetic properties, e.g. like low coercivity. Both porosity and grain size are influenced by the volume energy density (VED) used during additive manufacturing (AM) and are relatively independent of the part geometry. Additional factors like residual stresses, also affecting the magnetic properties, are not only influenced by the VED but also the part geometry and are distributed irregularly. Based on this, the geometry independent adjustment of residual stresses is only possible to a limited extent. Due to this, it is of high interest whether the sole consideration and adaption of grain size and porosity is sufficient to reach and assure soft magnetic properties for Ni50Fe50 in as-built condition. In this study, it is investigated whether soft magnetic properties can be achieved during AM of a Ni50Fe50 alloy using a standard laser powder bed fusion (PBF-LB) process by varying the used VED. The influence of increasing VEDs of up to 667 J/mm³ in the manufacturing process on grain size, porosity, saturation flux density and coercivity is analyzed. It could be shown that in a defined parameter field, the magnetic properties can be improved with increasing energy density, as larger grains are formed, while the relative density is not decisively reduced (minimal coercivity 184 A/m). However, it could also be shown that a standard PBF-LB process and the sole consideration of grain size and porosity is not applicable to reach soft magnetic properties (coercivity of < 100 A/m) in as-built condition and additional characteristics like residual stresses need to be taken into consideration in future works.