A Combinatorial Approach for Assessing the Magnetic Properties of High Entropy Alloys: Role of Cr in AlCo_xCr_1–xFeNi

Abstract

A combinatorial assessment of composition‐microstructure‐magnetic property relationships in magnetic high entropy AlCoxCr1‐xFeNi alloy (0 ≤ x ≤ 1) system has been carried out using compositionally graded alloys fabricated via laser additive manufacturing. At one end, the AlCoFeNi composition (x = 1) consisted of equiaxed B2 grains, exhibiting very early stages of phase separation (only compositional partitioning) into Ni–Al rich and Fe–Co rich regions within grains of the B2 phase. At the other extreme, the AlCrFeNi composition (x = 0) exhibited grains with pronounced spinodal decomposition, resulting in a B2 + bcc microstructure with the degree of spinodal decomposition progressively increasing with Cr content in these AlCoxCr1–xFeNi alloys. While the saturation magnetization (Ms) monotonically increases six times from x = 0 to x = 1, the coercivity (Hc) variation is non‐monotonic, increasing seven times from x = 0 to x = 0.4, and subsequently decreasing fourteen times from x = 0.4 to x = 1.0. The magnetic phase transition temperature (Tc) for these alloys also increases monotonically with increasing Co content with a second phase transition exhibited in a certain range of compositions between x = 0.6 to x = 0.8. Such substantial changes in the magnetization behavior and properties of magnetic high entropy systems opens possibilities of tuning these alloys for specific soft or hard magnetic component applications.

Mössbauer analysis of compositional tuning of magnetic exchange interactions in high entropy alloys

“…al on FeCoCrNi alloys. [7][8][9] The multiple similarly sized atoms mixed in relatively equiatomic amounts in these alloys lead to a 2 nd order magnetic transition, which is broadened due to the distributed exchange interactions arising from the disorder, [10][11][12][13][14] and allows Tc tuning and control of the refrigeration capacity, which leads to a broader transition range than seen in traditional alloys. This is a novel approach to increasing the refrigeration capacity of a magnetocaloric material that does not rely on physical processing (ball milling, cold rolling, etc) to broaden the temperature range.…”

Phase Engineering of High‐Entropy Alloys

“…The work combined experiments with DFT calculations to determine the balance between the surface and interfacial energies of the observed phases, which is particularly useful in elucidating the complex architectures of HEAs containing more than four phases. Since greater compositional diversity and structural complexity have been the tendency, we conclude the relationship between elements and phase numbers of HEAs based on the large numbers of reports, which is illustrated in Figure 9,13,25,63–75. It shows that the compositions of HEAs reach up to eight elements, and the number of phases achieves four.…”

“…Research has shown that HEAs could get fine soft magnetic properties with high magnetization and low coercivity by selecting suitable elements and compositions. Banerjee et al explored the role of Cr in AlCo x Cr 1− x FeNi (0 ≤ x ≤ 1) to study the magnetic properties 70. The hysteresis loops for AlCo x Cr 1− x FeNi are illustrated in Figure a.…”

“…a) Magnetizations ( M ) as a function of applied magnetic field ( H ) for NiAlFeCo x Cr 1– x HEA. Reproduced with permission 70. Copyright 2017, John Wiley and Sons.…”

“…Additionally, Dolinšek et al reported that the volume fraction of FCC bulky dendrites could decide the ratio of the ferromagnetic magnetization versus the superparamagnetic magnetization 155. Banerjee et al discovered that the spinodal decomposition reduced the ferromagnetism and lowered the temperature of the ferromagnetic–paramagnetic transition 70. In addition to the tuning strategies mentioned above, other methods could adjust the magnetic properties effectively as well.…”