Microstructure and Mechanical Properties of Al–Co–Cr–Fe–Ni Base High Entropy Alloys Obtained Using Powder Metallurgy

Abstract

Four different compositions of high entropy alloys based on Al-Co-Cr-Fe and Al-Co-Cr-Fe-Ni systems were prepared using mechanical alloying and consolidation by spark plasma sintering. The chemical compositions of the studied alloys were experimentally selected to obtain a BCC solid solution and mixtures of BCC with FCC. The microstructure of the Al25Co25Cr25Fe25 (all in at%) high entropy alloy consisted of a matrix with a high concentration of Al, Co and Fe, in which spherical grains (50-200 nm) enriched in Cr were embedded. Both the matrix and grains had body centered cubic structures. The addition of nickel to a four-element system led to the formation of a multiphase composition. The microstructure of the Al20Co20Cr20Fe20Ni20, Al10Co30Cr20Fe35Ni5 and Al15Co30Cr15Fe40Ni5 HEAs consisted of fine grains measuring 50-500 nm composed of: AlNi-B2, BCC phase, FCC or BCC solid solutions and σ-sigma phase, respectively. The complex structure of the studied samples resulted in changeable mechanical properties. The highest compression strength of 3920 MPa was accompanied by an increased yield strength of 3500 MPa, and a low strain of 0.7%, for the Al25Co25Cr25Fe25 alloy. The addition of Ni led to the formation of plastic FCC phases responsible for a decrease in strength with increases in ductility, which, in the new non-equiatomic Al10Co30Cr20Fe35Ni5 high entropy alloy reached 6.3% at a yield strength of 1890 MPa and compression strength of 2230 MPa. The conducted abrasion studies revealed that non-equilibrium high entropy alloys have the highest abrasion resistance.

Novel Co-Cu-Based Immiscible Medium-Entropy Alloys with Promising Mechanical Properties

“…The initial concept of HEAs is defined as a single phase with equiatomic or near-equiatomic compositions [1]. However, the range of alloy design in HEA/MEAs has been expanded to non-equiatomic and/or multiphase alloys [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Recently developed ferrous MEAs are representative types of non-equiatomic MEAs [8], which utilize phase metastability, resulting in transformationinduced plasticity.…”

“…Recently developed ferrous MEAs are representative types of non-equiatomic MEAs [8], which utilize phase metastability, resulting in transformationinduced plasticity. Meanwhile, the design of multiphase HEAs/MEAs to enhance yield Metals 2021, 11, 238 2 of 13 strength (YS) is widely adopted through precipitation [9][10][11][12][13][14], martensitic transformation [10,15,16], and eutectic reaction [17][18][19][20][21]. In particular, many research groups focus on heterogeneous HEAs developed by the formation of multiple domains using heterogeneities in composition [22,23], grain size [24,25], and crystal structure [17][18][19]26].…”

Deformation behavior of high-entropy alloy system Al – Co – Cr – Fe – Ni achieved by wire-arc additive manufacturing

“…В работе [11] показано, что микроструктура ОЦК высокоэнтропийного сплава Al25Co25Cr25Fe25, полученного искровым плазменным спеканием, состоит из матрицы с высокой концентрацией алюминия, кобальта и железа, в которую были внедрены обогащенные хромом сферические частицы (50 -200 нм). Кроме того, обнаружено небольшое количество карбидов Me 23 C 6 .…”

TEM and High Resolution TEM Investigation of Phase Formation in High Entropy Alloy AlCrFe2Ni2

“…Thermodynamically, Fe and Cr tend to concentrate more in a disordered FCC solid solution phase, while Ni and Al are typically concentrated in the ordered BCC arrangement (B2 phase). When the cooling rate is extremely high (such as in additive manufacturing) there is not enough time for the solidification route to go through the formation of an FCC phase, and a spinodal decomposition occurs, partitioning the alloy to Fe-and Cr-rich regions and Al-and Ni-rich regions (Wang et al, 2008;Manzoni et al, 2013;Dong et al, 2016;Munitz et al, 2016;Rogal et al, 2019;Li Z. et al, 2020). Both regions possess a BCC crystal structure, with the Cr-Fe-rich phase being a configurationally disordered solid solution, and the Al-Ni-rich phase being an ordered B2 (Manzoni et al, 2013;Rogal et al, 2019;.…”