Formation of L1₀ Ordering in FeNi by Mechanical Alloying and Field-Assisted Heat Treatment: Synchrotron XRD Studies

Abstract

L10-ordered FeNi, tetrataenite, found naturally in meteorites is a predilection for next-generation rare-earth free permanent magnetic materials. However, the synthesis of this phase remains unattainable in an industrially relevant time frame due to the sluggish diffusion of Fe and Ni near the order–disorder temperature (593 K) of L10 FeNi. The present work describes the synthesis of ordered L10 FeNi from elemental Fe and Ni powders by mechanical alloying up to 12 h and subsequent heat treatment at 623 K for 1000 h without a magnetic field and for 4 h in the presence of 1.5 T magnetic field. Also, to address the ambiguity of L10 phase identification caused by the low difference in the X-ray scattering factor of Fe and Ni, synchrotron-based X-ray diffraction is employed, which reveals that 6 h milling is sufficient to induce L10 FeNi formation. Further milling for 12 h is done to achieve a chemically homogeneous powder. The phase fraction of L10-ordered FeNi is quantified to ∼9 wt % for 12 h milled FeNi, which increases to ∼15 wt % after heat treatment. Heat treatment of the milled powder in a magnetic field increases the long-range order parameter (S) from 0.18 to 0.30. Further, the study of magnetic properties reveals a decrease in magnetic saturation and a slight increase in coercivity with the increase in milling duration. At the same time, heat treatment in the magnetic field shows a considerable increase in coercivity.

Laser Melting of Mechanically Alloyed FeNi: A Study of the Correlation between Microstructure and Texture with Magnetic and Physical Properties

“…Furthermore, the (100) superlattice peak of L1 0 FeNi coincides with the (311) fundamental peak of NiFe 2 O 4 . Spontaneous formation of NiFe 2 O 4 is possible during material handling and characterization. , Figures d and d show XRD patterns in the range of 42–45° of Figures a and a, respectively. An increase in the intensity of the (111) fundamental peak from the powder form to the laser-melted samples is observed, which can be attributed to the increase in the crystallinity of the sample during recrystallization.…”

“…The Fe and Ni powders were mixed in an atomic ratio of 1:1 and mechanically alloyed using a dual-drive planetary ball mill. Our recent study has reported detailed work on the mechanical alloying of FeNi (50–50 atom %) alloy . Mechanically alloyed FeNi powder was mixed with camphor (Sigma-Aldrich, purity 96%) to make pellets of 15 mm diameter and ∼4 mm height at an applied pressure of ∼270 MPa for 5 min, using a uniaxial press (Kimaya Engineers, India).…”

“…Our recent study has reported detailed work on the mechanical alloying of FeNi (50–50 atom %) alloy. 20 Mechanically alloyed FeNi powder was mixed with camphor (Sigma-Aldrich, purity 96%) to make pellets of 15 mm diameter and ∼4 mm height at an applied pressure of ∼270 MPa for 5 min, using a uniaxial press (Kimaya Engineers, India). Before laser melting, the pellets were heated in a debinding furnace (Nano tec, India) at 473 K to remove the binder.…”

“…Further heat treatment for 4 h under an applied magnetic field of 1.5 T was carried out in an argon atmosphere. Details of the furnace are reported in ref ( 20 ). 20 Finally, the samples were quenched with argon at ∼40 °C/min to room temperature under a magnetic field.…”

“…Details of the furnace are reported in ref ( 20 ). 20 Finally, the samples were quenched with argon at ∼40 °C/min to room temperature under a magnetic field.…”