The formation of polytwinned structures in FePt and FePd alloys

Zhang, B.; Lelovic, M.; Soffa, W.A.

doi:10.1016/0956-716x(91)90455-a

Cited by 74 publications

(47 citation statements)

References 9 publications

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“…The L1 0 phase is believed to form by nucleation and growth processes through a thermodynamically first-order chemical disorder-order phase transformation from a parent low-anisotropy fcc (A1-type) phase below a critical chemical order-disorder temperature T OD [9,10]. While isothermal annealing at temperatures below T OD is usually sufficient to promote L1 0 phase formation in related systems such as FePd and FePt [11], the task of obtaining the L1 0 phase in the FeNi system is quite difficult due, in part, to its very low T OD of 320 C [12] and to the extremely sluggish diffusion rate of Ni in the iron host at that temperature [8,13]. For comparative purposes, T OD for the L1 0 -type ferrous compounds FePd and FePt are 680 C and 1300 C, respectively [14], temperatures at which atomic mobilities are much greater.…”

Section: Introductionmentioning

confidence: 99%

Discovery of process-induced tetragonality in equiatomic ferromagnetic FeNi

et al. 2016

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a b s t r a c tSynthesis of a new tetragonal phase at the equiatomic composition in the archetypal binary Fe-Ni phase diagram is reported. This new phase is proposed as a transitional phase linking cubic FeNi with the chemically ordered tetragonal L1 0 FeNi compound, tetrataenite, of interest as a new advanced permanent magnetic material. This new tetragonal phase was created in a selection of nominally equiatomic FeNi alloys, made either from natural Fe and Ni or from natural Fe combined with the 62 Ni isotope, via application of high-strain processing methods followed by an annealing protocol. High-resolution neutron diffraction affirms that all unprocessed samples adopt the A1-type cubic structure (space group Fm3m) while all fully processed samples adopt the chemically disordered A6-type tetragonal structure (space group I4/mmm). Magnetic characterization documents a decrease in the initial magnetic susceptibility of deformed samples after annealing, evidencing a processing-induced increase in magnetic anisotropy that may be entirely accounted for by the measured tetragonal distortion. It is proposed that this new phase is a precursor to the formation of tetrataenite (L1 0 FeNi, space group P4/mmm), a meteoritic mineral of high magnetization and appreciable magnetocrystalline anisotropy that requires extraordinarily long cooling periods to form in nature. These results furnish new fundamental information as well as engineering insight for terrestrial synthesis of tetrataenite on industrial timescales, with high relevance for the creation of next-generation permanent magnets comprised entirely of easily accessible, earth-abundant elements.

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Section: Introductionmentioning

confidence: 99%

Discovery of process-induced tetragonality in equiatomic ferromagnetic FeNi

et al. 2016

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“…1 in which three orientation variants are formed due to the cubic-tetragonal lowering of the symmetry. In the past the morphological growth dynamics of these variants have been studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) [1][2][3][4][5], in order to understand the high uniaxial magnetocrystalline anisotropy of L1 0 -ordered crystals as controlled by the variant selection during the transformation. In contrast to the growth dynamics, the characteristics of anti-phase boundaries (APBs) have not been sufficiently clarified in spite of the fact that a high density of APBs are continuously interacting in the dynamical growth process of the variants.…”

Section: Introductionmentioning

confidence: 99%

Determination of the atomic width of an APB in ordered CoPt using quantified HAADF-STEM

Akamine

Bos

Gauquelin

et al. 2015

Journal of Alloys and Compounds

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“…[18] The ordered phase (L1 0 ) exhibits a significant tetragonality along the c-axis leading to a high magnetic anisotropy. Ordered FePd alloys are usually characterized by a high density of twins that relax strains resulting from the nucleation and growth of the tetragonal phase.…”

Section: Introductionmentioning

confidence: 99%

Optimization of the Magnetic Properties of FePd Alloys by Severe Plastic Deformation

et al. 2010

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A FePd alloy was nanostructured by severe plastic deformation following two different routes: ordered and disordered states were processed by high pressure torsion (HPT). A grain size in a range of 50 to 150 nm is obtained in both cases. Severe plastic deformation induces some significant disordering of the long range ordered L1 0 phase. However, Transmission Electron Microscopy (TEM) data clearly show that few ordered nanocrystals remain in the deformed state. The deformed materials were annealed to achieve nanostructured long range ordered alloys. The transformation proceeds via a first order transition characterized by the nucleation of numerous ordered domains along grain boundaries. The influence of the annealing conditions (temperature and time) on the coercivity was studied for both routes. It is demonstrated that starting with the disorder state prior to HPT and annealing at low temperature (400°C) leads to the highest coercivity (about 1.8 kOe).

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The formation of polytwinned structures in FePt and FePd alloys

Cited by 74 publications

References 9 publications

Discovery of process-induced tetragonality in equiatomic ferromagnetic FeNi

Discovery of process-induced tetragonality in equiatomic ferromagnetic FeNi

Determination of the atomic width of an APB in ordered CoPt using quantified HAADF-STEM

Optimization of the Magnetic Properties of FePd Alloys by Severe Plastic Deformation

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