Pressure–Composition Phase Diagram of Fe–Ni Alloy

Abstract

We investigated the structural phase transitions of FeNi alloys under hydrostatic pressure conditions at 298 K by examining the X-ray diffraction patterns of polycrystalline samples with Ni contents of 5%31.6%, and pressurecomposition phase diagram was established for the pressure range of 015 GPa. The diagram comprised three structural phases: bcc, fcc, and hcp, and these all coexisted in 25% Ni at 11 GPa during compression and in 23% Ni at 7 GPa during decompression. During both processes, low-and high-pressure phases coexisted. During the pressure-induced structural transitions, significant hysteresis was also observed. The 27% Ni alloy showed the two-stage transition: bccfcchcp, and the fcc phase was quenched to ambient pressure. For the 523% Ni alloys, a bcchcp transition was observed at high pressure. As the Ni content increased, the transition pressure decreased, and the volume reduction of the bcchcp transition also decreased due to the increase in the atomic volume of the hcp phase. The transition pressure from fcc to hcp rapidly increased with the Ni content. Compression curves of 29.9% Ni and 31.6% Ni alloys exhibited an anomaly at 2.0 and 2.9 GPa, respectively, and the compression anomaly was attributed to the magnetic transition.

Magnetism of Body‐Centered Cubic Fe‐Ni Alloys Under Pressure: Strain‐Enhanced Ferromagnetism at the Phase Transitions

“…A 200 μm hole bored in a work hardened rhenium gasket ( h = 80 μm) was loaded with Fe 84 Ni 16 together with Si gel and rubies, identical to the SIRM experiments; rubies were placed on the side with the solid, nonperforated diamond. We used Fe 84 Ni 16 due to its lower bcc‐hcp transition pressure (∼9–10 GPa, Huang et al., 1988 and ∼12 GPa, Akahama et al., 2020) than that for Fe 100 Ni 0 , as the highest pressure attainable by the partially perforated diamond was uncertain. We first measured the XAFS and XMCD at the K‐edge of Fe in the diamond cell at ambient P and T as a function of applied field strength in order to know the field intensity required to attain saturation (Figure 4a).…”

“…Huang et al (1988) found that the bcc to hcp phase transition decreases in pressure with increasing Ni, being ~11 GPa and ~8 GPa for Ni concentrations of 10% and 25% respectively. Using a monochromatic synchrotron radiation X-ray source, Akahama et al (2020)…”

“…Using a monochromatic synchrotron radiation X‐ray source, Akahama et al. (2020) found that the onset pressure of the bcc to hcp transition decreases 0.2 GPa per at% Ni from 0% to 15% Ni, and then remained constant with increasing amounts of Ni. The reverse transition (hcp to bcc) pressure upon decompression likewise decreased with increasing Ni concentration yet was shifted ca.…”

“…The reverse transition (hcp to bcc) pressure upon decompression likewise decreased with increasing Ni concentration yet was shifted ca. 6 GPa below the bcc to hcp transition pressures (Akahama et al., 2020). The transition from bcc to hcp occurs via a diffusionless, martensic mechanism that does not involve movement of atoms over distances larger than the lattice dimensions (Bassett & Huang, 1987; Huang et al., 1988).…”

An accurate empirical formula for determining the density of heat-resistant nickel alloys

“…Принято считать, что структура ЖНС представляет собой γ-твердый раствор легирующих элементов в никелевой матрице (геометрическая модель -ГЦК-структура [13]) и дисперсных выделений γ'-фазы на основе Ni 3 Al при очень близких периодах их кристаллических решеток, дающих взаимное несоответствие («мисфит») не выше 0.5 % и результирующим параметром ячейки решетки, рассчитывающимся как арифметическое среднее параметров решеток γ-и γ'-фаз. Этот фактор необходимо в той или иной степени учесть при расчетах плотности ЖНС.…”