AlCoCrCuFeNi-Based High-Entropy Alloys: Correlation Between Molar Density and Enthalpy of Mixing in the Liquid State (original) (raw)
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Metals
Quinary AlCoCrFeNi high entropy alloy (HEA) is one of the most studied alloys in the recent decade due to its outstanding properties. However, it is still far from becoming an applicable industrial alloy. To our understanding, in order to promote this, the role of elements, constituting the quinary alloy, needs to be defined. Knowing the role of each element, modification of the quinary alloy toward minimization of its disadvantages will be possible. In the current research, we shed some light on this subject, presenting a thorough investigation of the microstructure (carried out using scanning and transmission electron microscopy) and mechanical properties, performed by microhardness and fractography post small punch test (SPT), of five equiatomic quaternary alloys, constituting the quinary system, namely: CoCrFeNi, AlCoFeNi, AlCoCrNi, AlCoCrFe, and AlCrFeNi. CoCrFeNi (i.e., w/o Al) was found to be Face Centered Cubic (FCC) solid solution, exhibiting relatively low micro-hardness a...
Phase formation in mechanically alloyed AlxCoCrCuFeNi (x = 0.45, 1, 2.5, 5 mol) high entropy alloys
Alloying behavior and phase transformations in AlxCoCrCuFeNi (x = 0.45, 1, 2.5, 5 mol) multi-component high entropy alloys that are synthesized by mechanical alloying were studied. Two FCC phases along with a BCC phase were formed in Al0.45CoCrCuFeNi and AlCoCrCuFeNi, while a single B2 phase was observed in higher Al containing alloys Al2.5CoCrCuFeNi and Al5CoCrCuFeNi. DSC analysis indicates that BCC phase present in the alloys could be Fe–Cr type solid solution. A detailed analysis suggests that two melting peaks observed during DSC in lower Al containing alloys can be attributed to that of Cu–Ni and Fe–Ni FCC solid solutions. The BCC phase disappears in Al0.45CoCrCuFeNi and AlCoCrCuFeNi at high temperatures during DSC. However, Al5CoCrCuFeNi retains its B2 structure despite of heating in DSC. Further, phases present in these alloys retain nanocrystallinity even after exposure to high temperatures. A critical analysis is presented to illustrate that solid solution formation criteria proposed for high entropy alloys in the literature are unable to explain the phase formation in the present study of alloys. Besides, these criteria seem to be applicable to high entropy alloys only under very specific conditions.► Homogeneous HEA of AlxCoCrCuFeNi (x = 0.45 – 5 mol) are made by mechanical alloying. ► Increase in Al results in microstructural change from three phases to single phase. ► B2 compound is the stable phase in alloy with highest Al content, Al5CoCrCuFeNi. ► Nanocrystallinity is retained even after exposure to high temperature of 1480 °C. ► Existing criteria of phase formation in HEA are deficient to explain our results.
On the elemental effect of AlCoCrCuFeNi high-entropy alloy system
Materials Letters, 2007
The AlCoCrCuFeNi high-entropy alloy system was synthesized using a well-developed arc melting and casting method. Their elemental effect on microstructures and hardness was investigated with X-ray diffraction, scanning electron microscopy and Vickers hardness testing. The alloys exhibit quite simple FCC and BCC solid solution phases. Co, Cu and Ni elements enhance the formation of the FCC phase while Al and Cr enhance that of the BCC phase in the alloy system. BCC phases form a spinodal structure during cooling. Copper tends to segregate at the interdendrite region and forms a Cu-rich FCC phase. Low copper content renders the interdendrite as a thin film and the as-cast structure like recrystallized grain structure. The formation of BCC phases significantly increases the hardness level of the alloy system. The strengthening mechanism is discussed.
Entropy-driven phase stability and slow diffusion kinetics in an Al0.5CoCrCuFeNi high entropy alloy
Previous work on the stability of the solid solution phases in the high entropy alloys is inconclusive. We used a series of thermo-mechanical treatments to study the stability of the solid solution phases in a high-entropy Al0.5CoCrCuFeNi alloy. The solid solution phases were found to be stable, against the intermetallic compounds, at high temperatures >850 °C and at low temperatures <300 °C. At intermediate temperatures, however, the intermetallic σ-phase co-existed with the solid solution phases. The experimental observations were verified by the thermodynamic calculation results. The mechanisms for the phase stability, both at equilibrium and after quenching-equivalent annealing treatments, were discussed, and the roles of high entropy and slow diffusion kinetics were highlighted.
Processing and Properties of AlCoCrFeNi High Entropy Alloys: A Review
Advances in Materials Science and Engineering
The aim of this study is to carry out a focused literature review on the mechanical and tribological behaviour of AlCoCrFeNi High Entropy Alloys (HEA). HEAs are a proficient class of alloys designed by the use of several constituent alloying elements in equiatomic or close to equiatomic ratios. In view of their distinctive property range, there has been huge attention on this class of alloys. Among the various group of HEAs, AlCoCrFeNi-based HEAs have attracted interest due to their enhanced properties. Various AlCoCrFeNi-based HEAs are developed by adding additional elements such as Mo, Ti, and Zr. The effect of these alloying constituents on the mechanical, metallurgical, and tribological performance of the AlCoCrFeNi HEA is discussed in detail. In addition to that, the various techniques used to produce these HEAs are also discussed.
Decomposition in multi-component AlCoCrCuFeNi high-entropy alloy
Acta Materialia, 2011
The decomposition of an equiatomic AlCoCrCuFeNi high-entropy alloy produced by splat quenching and casting was investigated by the analytical high resolution methods: transmission electron microscopy and three-dimensional atom probe. It could be shown that splat-quenched alloy consisted of an imperfectly ordered body-centred cubic phase with a domain-like structure, whereas normally cast alloy formed several phases of cubic crystal structure. The cast alloy decomposed into both dendrites and interdendrites. A detailed local compositional analysis carried out by atom probe within the dendrites revealed that the alloying elements in the Ni–Al-rich plates and Cr–Fe-rich interplates are not randomly distributed, but segregate and form areas with pronounced compositional fluctuations. Cu-rich precipitates of different morphologies (plate-like, spherical and rhombohedron-shaped) could also be found in the dendrites. The results are discussed in terms of segregation processes governed by the enthalpies of mixing of the binary systems.
Thermodynamic properties of liquid Al-Si and Al-Cu alloys
Journal of Thermal Analysis and Calorimetry, 2002
The partial and integral enthalpies of mixing in liquid Al-Si and Al-Cu alloys were determined by high-temperature isoperibolic calorimetry at 1750±5 and 1590±5, respectively. The thermodynamic properties of Al-Si melts were also studied by electromotive force method in temperature range 950-1270 K. The partial and integral excess Gibbs free energies of mixing in liquid Al-Si and Al-Cu alloys were calculated from literature data on thermodynamic activity of aluminium. The comparison of our experimental results with literature data has been performed.
Metals, 2017
Alloying aluminum offers the possibility of creating low-density high-entropy alloys (HEAs). Several studies that focus on the system AlCoCrFeNiTi differ in their phase determination. The effect of aluminum on the phase composition and microstructure of the compositionally complex alloy (CCA) system AlxCoCrFeNiTi was studied with variation in aluminum content (molar ratios x = 0.2, 0.8, and 1.5). The chemical composition and elemental segregation was measured for the different domains in the microstructure. The crystal structure was determined using X-ray diffraction (XRD) analysis. To identify the spatial distribution of the phases found with XRD, phase mapping with associated orientation distribution was performed using electron backscatter diffraction. This made it possible to correlate the chemical and structural conditions of the phases. The phase formation strongly depends on the aluminum content. Two different body-centered cubic (bcc) phases were found. Texture analysis prov...
A new approach for the design of alloy systems with multiprincipal elements is presented in this research. The Al x CoCrCuFeNi alloys with different aluminum contents (i.e., x values in molar ratio, x ϭ 0 to 3.0) were synthesized using a well-developed arc-melting and casting method. These alloys possessed simple fcc/bcc structures, and their phase diagram was predicted by microstructure characterization and differential thermal analyses. With little aluminum addition, the alloys were composed of a simple fcc solid-solution structure. As the aluminum content reached x ϭ 0.8, a bcc structure appeared and constructed with mixed fcc and bcc eutectic phases. Spinodal decomposition occurred further on when the aluminum contents were higher than x ϭ 1.0, leading to the formation of modulated plate structures. A single ordered bcc structure was obtained for aluminum contents larger than x ϭ 2.8. The effects of high mixing entropy and sluggish cooperative diffusion enhance the formation of simple solid-solution phases and submicronic structures with nanoprecipitates in the alloys with multiprincipal elements rather than intermetallic compounds.
Phase evolution and thermal stability of mechanically alloyed CoCrCuFeNi high entropy alloy
Materials Research Express, 2019
In the present investigation, a newly designed composition of equiatomic AlCrFeCoNiZn high-entropy alloy (HEA) has been synthesized by mechanical alloying. The milled powder after 30 h exhibited the formation of a single solid solution phase of BCC crystal structure with lattice parameter, a = 2.87 ± 0.02 Å. Decomposition of the single-phase BCC structure into the two-phase, tetragonal (Cr-Co)-based r phase (a = 8.81 Å , c = 4.56 Å)-and L1 2 (a = 3.59 ± 0.02 Å)-type intermetallics was observed at temperature of * 800°C (1073 K). However, after heat treatment of the 30 h milled powder at the temperatures of 300°C (573 K) and 600°C (873 K), similar type of phases was also noticed to coexist along with B2 (a = 2.87 ± 0.03 Å)-type phase. This behaviour of the alloy confirms the diffusive nature of the phase transformation. The consolidated bulk alloy exhibited similar type of phases after sintering at 950°C (1223 K).