Kinetics of order-disorder transformation of L1 2 FeNi 3 in the Fe-Ni system J. Liu a , L.J. Riddiford a , C. Floristean a , F. Goncalves-Neto a , M. Rezaeeyazdi b , L.H. Lewis b, c , K. Barmak a, * a Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA b Department of Chemical Engineering, Northeastern University, Boston, MA 02115, USA c Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115, USA article info Article history: Received 29 June 2016 Received in revised form 3 August 2016 Accepted 5 August 2016 Available online 6 August 2016 Keywords: L1 2 FeNi 3 L1 0 FeNi Tetrataenite Order-disorder transformation abstract The Fe-Ni system has seen a resurgence of interest for the development of high magnetocrystalline anisotropy alloys. The kinetics of the chemical order-disorder phase transformation of the ferromagnetic test-bed compound L1 2 FeNi 3 were quantified using differential scanning calorimetry data obtained from annealed meltspun Fe-75 at% Ni ribbons. The isothermal transformation kinetics are found to be well described by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation with a determined Avrami expo- nent of unity, consistent with one-dimensional growth of the chemically-disordered A1 phase from the chemically-ordered L1 2 FeNi 3 parent phase. The determined activation energy for the transformation from the chemically-ordered L1 2 structure to the disordered A1 structure in FeNi 3 , 3.1 ± 0.1 eV, is equal to that reported for the L1 0 -to-A1 order-disorder phase transformation of the FeNi phase that is found in meteoritic specimens. These results confirm that the L1 2 phase of FeNi 3 is a suitable model phase for investigation of formation aspects of the tetragonal L1 0 -type FeNi phase, also known as tetrataenite, which exhibits extremely sluggish formation kinetics but possesses appreciable magnetocrystalline anisotropy and excellent saturation magnetization that is of interest for sustainable permanent magnet applications. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Quantifying the kinetics of phase transitions in functional ma- terials is a necessary first step to controlling and tailoring such phase transitions to defined parameters. In particular, motivated by recent interest in the development of new advanced magnetic materials made from sustainable and accessible elements, it is of interest to investigate and understand kinetic features that govern chemical disorder-order phase transitions of ferromagnetic com- pounds within the Fe-Ni binary system. The equiatomic FeNi compound with the tetragonal L1 0 -type chemically ordered struc- ture, known as tetrataenite, has attracted a great deal of attention in recent years for permanent magnet applications [1e 13]. Tetra- taenite possesses a significant magnetocrystalline anisotropy en- ergy and a high saturation magnetization that combine to yield an estimated maximum magnetic energy product (BH) max of 42 MGOe [1], approximately 66% of that of Nd 2 Fe 14 B-based rare earth supermagnets. This projected energy product allows tetrataenite to be contemplated as an important, economical and sustainable magnet to fill the performance gap between low-energy-product ferrite magnets and rare-earth magnets. However, the kinetics of the phase transformation in FeNi from the disordered cubic A1- type structure to the L1 0 -type structure are extraordinarily slug- gish, with natural ordered phase formation found in meteorites subjected to experimentally inaccessible cooling periods, on the order of hundreds of millions of years [14,15]. In contrast to that of tetrataenite, the chemical order-disorder phase transition of the closely-related ferromagnetic compound FeNi 3 , which transitions from the disordered A1-type structure to the L1 2 -type structure with increased temperature, is readily achieved on laboratory timescales [16e18]. This characteristic makes it an excellent proxy for study of the conditions to promote the formation of L1 0 -type FeNi. In this work, kinetic aspects of the chemical disordering phase transformation of L1 2 -type FeNi 3 are probed and quantified to furnish insight into formation aspects of L1 0 -type FeNi. * Corresponding author. E-mail address: kb2612@columbia.edu (K. Barmak). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2016.08.036 0925-8388/© 2016 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 689 (2016) 593e598