Phase Equilibria and Thermodynamic Evaluation Approximating Short-range Ordering Energy in the Fe–Rh Binary System

Abstract

Phase equilibria between the a (A2), aЈ (B2) and g (A1) phases in the Fe-Rh binary system were investigated using electron probe micro-analysis (EPMA) and differential scanning calorimetry (DSC) techniques. The A2/B2 order-disorder transformation temperature was also examined by a transmission electron microscope (TEM) observations and high-temperature X-ray diffraction (HTXRD). It was confirmed that while the transition temperature from the a (A2) phase to the g (A1) phase decreases with increasing Rh content up to about 20 at% Rh, the b.c.c. region is stabilized by further Rh addition in the composition range between about 20 and 50 at% Rh, and then again the stability of b.c.c. phase decreases in the composition region over 50 at% Rh. It was also shown by TEM observation and HTXRD examination that the compositions of the phase boundary of the A2/B2 ordering at 500°C and 600°C were determined to be 16.5 and 19.1 at% Rh, respectively. On the basis of those experimental results, a thermodynamic analysis was carried out. The results of the thermodynamic calculation suggest that the anomalous behavior of the stability of the b.c.c. phase is caused by the A2/B2 ordering.KEY WORDS: CALPHAD; order-disorder transition; short-range ordering; magnetic ordering; phase stability. terials were Fe (99.9 mass%) and Rh (99.97 mass%), and the composition range of the prepared alloys was Fe-(10-55)at%Rh as listed in Table 1. Each as-cast specimen was sealed in an evacuated quartz capsule, back-filled with argon, and annealed at temperatures between 650°C and 1 350°C for duration of between 24 h and 4 380 h. After the heat-treatment for equilibration, the specimens were quenched into ice water. Results of chemical analysis of ascast specimens are listed in Table 1. After microstructure examination by an optical microscope, equilibrium compositions were determined by electron probe microanalysis (EPMA: JEOL JXA-8100) using a standard calibration method. The transition temperature of some alloys at about 20 at% Rh was also determined by differential scanning calorimetry (DSC: SEIKO DSC-320) at heating rate of 3°C/min.In order to determine the A2/B2 ordering temperature, DSC measurement, transmission electron microscopic (TEM: JEOL JEM-2000EX II) examination and high temperature X-ray diffraction (HTXRD: Phillips X'part) were performed. The specimens for the TEM observation were solution-treated at 1 300°C for 1 h, cooled down to 500°C or 600°C, and aged at those temperatures for 72 h. The centers of disks cut from the as-aged specimens were processed into thin foils by dimple-grinding and ionmilling. TEM examination at room temperature was carried out on the thin foils. Powdered specimens were annealed at 1 300°C and analyzed by HTXRD at 500°C and 600°C. Experimental Results 3.1.Phase Equilibria between the a a (A2), a a (B2), g g (A1) Phases A typical example of the microstructure of the aЈ (B2)ϩg (A1) two-phase alloy annealed at 1 200°C for 96 h is shown in Fig. 2. It can be seen that the size of the precipitated aЈ (B2) phase i...

Tailoring magnetic frustration in strained epitaxial FeRh films

“…45 Reciprocal space maps (RSMs) on asymmetric W reflections (having an in-plane component of the scattering vector), yield 3.151(2) Å in-plane lattice constant, suggesting an almost fully relaxed growth of the W bufferlayer on MgO(001). 29 or partially B2-ordered (dotted) 46 FeRh.…”

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Solid-state synthesis, magnetic and structural properties of interfacial B2-FeRh(001) layers in Rh/Fe(001) films

“…Such an approach is justified by us for the well-studied Fe-Ni system 62 and made it possible to predict phase transformations in other binary metallic systems [46][47][48] . Therefore, further study of solidstate reactions in Rh/Fe films, depending on the composition, will make it possible to specify the low-temperature part of the Fe-Rh phase diagram, which still remains unknown 63 .…”

Magnetic properties of ordered polycrystalline FeRh thin films

“…The long-range magnetic order of A2-FeRh arises from the dominating short-range FM exchange interactions between Fe-Fe and Fe-Rh pairs over the competing AF Fe-Fe interactions at larger separations. 19,20 When the system is in between 20 and 50 at% of Rh, it goes into a chemically ordered bcc structure (B2). Then with x < 50, i.e.…”