Functional Grading Between Soft-Magnetic Fe–Co/Fe–Ni Alloys and the Effect on Magnetic and Microstructural Properties

Producing
soft magnetic alloys by additive manufacturing has the
potential to overcome cracking and brittle fracture issues associated
with conventional thermomechanical processing. Fe–Co alloys
exhibit high magnetic saturation but low ductility that makes them
difficult to process by commercial methods. Ni–Fe alloys have
good ductility and high permeability in comparison to Fe–Co,
but they suffer from low magnetic saturation. Functional grading between
Fe–Co and Ni–Fe alloys through blown powder directed
energy deposition can produce soft magnetic materials that combine
and enhance properties beyond the strengths of the individual magnetic
materials. This work focuses on the microstructure, crystal structure,
and magnetic properties of functionally graded Fe49Co49V2/Ni80Fe16Mo4 coupons. The grading between the two materials is found to refine
the microstructure, thereby improving the mechanical hardness without
the use of a nonmagnetic element. Postbuild thermal treatments are
found to recrystallize the microstructure and increase the grain size,
leading to improved magnetic properties. Analysis of crystal structures
provides an understanding of the solubility limits and phase equilibria
between the BCC (Fe–Co) and FCC (Ni–Fe) structures.
Success in functional grading of soft magnets may provide a pathway
toward improving energy conversion efficiency through strategic combinations
of high saturation and high strength materials.