Pressure-induced magnetovolume effect in CoCrFeAl high-entropy alloy

Abstract

High-entropy alloys (HEAs) composed of multiple-principal elements with (nearly) equimolar ratio establish a new conceptual framework for alloy design and hold a promise for extensive applications in industry, akin to the controlled expansion alloys (CEAs), such as Invar alloys. Spontaneously, one question emerges-would it be possible to synthesize a novel class of alloys combining the virtues of both CEAs and HEAs? Here, we report the pressure-induced magnetovolume effect in the body-centered-cubic CoCrFeAl HEA coupled with magnetic phase transitions from ferromagnetic to paramagnetic, and to non-magnetic states, originating from the successive collapses of local magnetic moments of Co and Fe. The observed magnetovolume anomalies, occurring in a progressive way, tailor appreciably the coefficient of thermal expansion of CoCrFeAl. These results further strengthen HEAs' anticipated potential for designing multifunctional materials in virtue of their multiple outstanding properties, and reveal possible routes for their future synthesis.

Magnetic properties of the complex concentrated alloy system CoFeNi0.5Cr0.5Alx

“…This however, indicates that increasing the Al stoichiometric ratio increases B2 stability, which leads to a corresponding increase in Curie temperature and in saturation magnetisation for fully formed NPs. The increase magnetisation of the BCC/B2 phase (on a phase transition from FCC stability on Al addition) has been previously noted in the literature 42 , which may be driven by increased magnetic ordering, as noted previously 13,43 . However, it is not clear that the changes in magnetic behaviour are solely related to the BCC/B2 structure as extrapolating the MT curves for the n-Al 0.5 sample using Bloch's law gives a magnetisation of 27 Am 2 /kg at 5 K (cf.…”

THERMAL STABILITY AND THERMAL EXPANSION BEHAVIOR OF AlFeCoNiCu AS-CAST HIGH-ENTROPY DUAL-PHASE ALLOY

“…An increase in the CTE with increasing temperature up to 1470К is observed for FeCoCrNiAl HEAs [40]. The anomalous CTE was reported for the CoCrFeAl HEA at high temperatures [41], where the temperature dependence of the linear CTE was measured up to 820K. The CTE of the CoCrFeAl alloy demonstrates two deviations from regular behavior: (1) at 430 K -720K, where the CTE remains almost constant, the anomaly arises due to the ferromagnetic to paramagnetic (FM-PM) phase transition; and (2) at 720 K -770K, where the CTE decreases with increasing temperature, reaching almost zero at around 770K.…”

“…The reference literature data on the thermal expansion of the AlFe-CoNiCu as-cast high-entropy alloy are unknown authors of this study. The obtained results were compared with existing literature for AlFeCoNiCu high-entropy alloys [38,40,41]. The average CTE of FeCoCrNi2Al and FeCoCrNiAl0.3 up to 1470K is (15.16±0.25)×10 -6 K -1 and (15.72 ± 0.35)×10 -6 K -1 , respectively [40].…”

“…Meanwhile, the sample length stays almost constant in the range of 760-775K, which resembles the Invar effect. The second anomaly should be interpreted as the paramagnetic (PM) to nonmagnetic (NM) phase transition [41]. Previously, the kinetics of the phase transformation of FCC to BCC during heating of a high-entropy Al0.5CoCrFeNi alloy was investigated by the thermal expansion method.…”

A Seawater‐Corrosion‐Resistant and Isotropic Zero Thermal Expansion (Zr,Ta)(Fe,Co)2 Alloy

“…The introduction of Ta will yield positive chemical pressure to the FeFe distance and affect the coupling between lattice and spin, similar to physical pressure. [45,46] We evaluated about 6 GPa chemical pressure in ZTFC (the elasticity modulus B of (Zr,A)Fe 2 (A = Zr, Hf, Lu) is about 170-210 GPa [47] ). The chemical pressure compresses the FeFe distance from 2.50 Å (x = 0.0) to 2.48 Å (ZTFC, x = 0.2) and weakens the FM state of alloys.…”