Effect of the aluminium content of AlxCrFe1.5MnNi0.5 high-entropy alloys on the corrosion behaviour in aqueous environments

High-entropy alloys (HEAs) are a newly developed family of multi-component alloys. The potentiodynamic polarization and electrochemical impedance spectroscopy of the Al_xCrFe_1.5MnNi_0.5 alloys, obtained in H₂SO₄ and NaCl solutions, clearly revealed that the corrosion resistance increases as the concentration of aluminium decreases. The Al_xCrFe_1.5MnNi_0.5 alloys exhibited a wide passive region, which extended >1000 mV in acidic environments. The Nyquist plots of the Al-containing alloys had two capacitive loops, which represented the electrical double layer and the adsorptive layer. SEM micrographs revealed that the general and pitting corrosion susceptibility of the HEAs increased as the amount of aluminium in the alloy increased.     

Effect of Aluminum Content on Microstructure and Mechanical Properties of Al x CoCrFeMo0.5Ni High-Entropy Alloys

High-entropy alloys Al _x CoCrFeMo_0.5Ni with varied Al contents (x = 0, 0.5, 1.0, 1.5, and 2.0) have been designed based on the Al _x CoCrCuFeNi system to improve mechanical properties for room and elevated temperatures. They have been investigated for microstructure and mechanical properties. As the aluminum content increases, the as-cast structure evolves from face-centered cubic dendrite + minor σ-phase interdendrite at x = 0 to B2 dendrite with body-centered cubic (bcc) precipitates + bcc interdendrite with B2 precipitates at x = 2.0. This confirms the strong bcc-forming tendency of Al. The room-temperature Vickers hardness starts from the lowest, HV 220, at x = 0, attains to the maximum, HV 720, at x = 1.0, and then decreases to HV 615 at x = 2.0. Compared with the base alloy system, the current alloy system has a superior combination of hardness and fracture toughness. In addition, Al _x CoCrFeMo_0.5Ni alloys except x = 0 display a higher hot hardness level than those of Ni-based superalloys, including In 718 and In 718 H, up to 1273 K and show great potential in high-temperature applications.     

Microstructure and mechanical performance of new Al0.5CrFe1.5MnNi0.5 high-entropy alloys improved by plasma nitriding

Effects of plasma nitriding at 525 °C on microstructure and mechanical performance of a brand-new Al_0.5CrFe_1.5MnNi_0.5 high-entropy alloy (HEA) were investigated. This alloy exhibits a large age hardening effect at temperatures from 600 to 800 °C and can be well-nitrided in the as-cast condition or the homogenized and furnace-cooled state. The nitrided layer has a thickness around 75 μm and a peak hardness level of Hv 1250 near the surface. The nitrided Al_0.5CrFe_1.5MnNi_0.5 alloys exhibit superior adhesive wear resistance to conventional nitrided steels by 25-54 times due to their much thicker highly-hardened layer and higher peak hardness than that of conventional steels.     

Direct active soldering of Al0.3CrFe1.5MnNi0.5 high entropy alloy to 6061-Al using Sn-Ag-Ti active solder

Al_0.3CrFe_1.5MnNi_0.5 high entropy alloys (HEA) have special properties. The microstructures and shear strengths of HEA/HEA and HEA/6061-Al joints were determined after direct active soldering (DAS) in air with Sn3.5Ag4Ti active filler at 250 °C for 60 s. The results showed that the diffusion of all alloying elements of the HEA alloy was sluggish in the joint area. The joint strengths of HEA/HEA and HEA/6061-Al samples, as analyzed by shear testing, were (14.20±1.63) and (15.70±1.35) MPa, respectively. Observation of the fracture section showed that the HEA/6061-Al soldered joints presented obvious semi-brittle fracture characteristics.     

Aluminum Alloying Effects on Lattice Types, Microstructures, and Mechanical Behavior of High-Entropy Alloys Systems

The crystal lattice type is one of the dominant factors for controlling the mechanical behavior of high-entropy alloys (HEAs). For example, the yield strength at room temperature varies from 300 MPa for the face-centered-cubic (fcc) structured alloys, such as the CoCrCuFeNiTi _x system, to about 3,000 MPa for the body-centered-cubic (bcc) structured alloys, such as the AlCoCrFeNiTi _x system. The values of Vickers hardness range from 100 to 900, depending on lattice types and microstructures. As in conventional alloys with one or two principal elements, the addition of minor alloying elements to HEAs can further alter their mechanical properties, such as strength, plasticity, hardness, etc. Excessive alloying may even result in the change of lattice types of HEAs. In this report, we first review alloying effects on lattice types and properties of HEAs in five Al-containing HEA systems: Al _x CoCrCuFeNi, Al _x CoCrFeNi, Al _x CrFe_1.5MnNi_0.5, Al _x CoCrFeNiTi, and Al _x CrCuFeNi₂. It is found that Al acts as a strong bcc stabilizer, and its addition enhances the strength of the alloy at the cost of reduced ductility. The origins of such effects are then qualitatively discussed from the viewpoints of lattice-strain energies and electronic bonds. Quantification of the interaction between Al and 3d transition metals in fcc, bcc, and intermetallic compounds is illustrated in the thermodynamic modeling using the CALculation of PHAse Diagram method.     

Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> High-Entropy Alloys

FeCrMoVTi _x (x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi _x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.     

FeCoNiCrCu0.5Alx高熵合金的结构和性能（英文）

研究Al含量和热处理对FeCoNiCrCu0.5Alx多主元高熵合金的相结构、硬度和电化学性能的影响规律。随着Al含量的增加,铸态合金的相结构由FCC相向BCC相转变。当x从0.5增加到1.5时,FeCoNiCrCu0.5Alx高熵合金的稳定结构由FCC结构向FCC+BCC双相结构转变。BCC相的硬度高于FCC相的,在氯离子及酸性介质中BCC相的耐腐蚀性均优于FCC相的。FeCoNiCrCu0.5Al1.0铸态合金具有高硬度和良好的抗腐蚀性能。     

Effect of Si/Ti additions on physico-mechanical and chemical properties of FeNiCrCo high entropy alloys manufactured by powder metallurgy technique

FeNiCrCoSi_x and FeNiCrCoTi_x (x=0, 0.3, 0.6, and 0.9 wt.%) high entropy alloys (HEAs) were prepared via the powder metallurgy technique. A homogenous distribution of the elements in all alloys due to the formation of a solid solution phase is observed. The density and hardness of the prepared HEAs are improved by Si and Ti additions, compared to FeNiCrCo HEA. The wear rate of the prepared alloys was studied at different loads and the results indicate that the alloys that contain 0.3 wt.% Si and 0.9 wt.% Ti have the lowest wear rates. X-ray diffraction, SEM, and EDX were used to understand the phases, grain sizes, and microstructures in different investigated HEAs. The effects of Si and Ti content on the corrosion behavior and surface morphologies of sintered FeNiCrCoSi_x and FeNiCrCoTi_x HEAs were studied by immersion in H₂SO₄, HNO₃, and HCl solutions. Uniform corrosion and localized pitting are observed in different sizes in the corrosive media used. Because of the smaller pit size and the reduced pit density, the FeNiCrCoSi_0.3 HEA has an excellent microstructure.     

Microstructure and Mechanical Properties of a Refractory CoCrMoNbTi High-Entropy Alloy

In this work, a new refractory high-entropy alloy, the Co-Cr-Mo-Nb-Ti system, was proposed as a family of candidate materials for high-temperature structural applications. CoCrMoNbTi _x (x values in terms of molar ratios, x = 0, 0.2, 0.4, 0.5 and 1.0) alloys were prepared by vacuum arc melting. The effects of variations in the Ti content on the phase constituents, microstructure and mechanical properties of the alloys were investigated using x-ray diffractometry, scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy and compressive testing. The results showed that the CoCrMoNbTi_0.4 alloy possessed a typical cast dendritic microstructure consisting of a single body-centered cubic (BCC) solid solution. Laves phases (Cr₂Nb and Co₂Ti) were formed in other alloys with different Ti contents. The results were discussed in terms of the mixing enthalpy, atomic size difference, electronegativity difference and valance electron concentrations among the elements within alloys. The alloy hardness exhibited a slightly decreasing trend as the Ti content increased, resulting from the coarser microstructure and reduced amount of Laves phases. Augmented Ti content increased the compressive strength, but decreased the ductility. Particularly, for the CoCrMoNbTi_0.2 alloy, the hardness, compressive strength and fracture strain were as high as 916.46 HV_0.5, 1906 MPa and 5.07%, respectively. The solid solution strengthening of the BCC matrix and the formation of hard Laves phases were two main factors contributing to alloy strengthening.     

Effects of Sc,Zr and Ti on the microstructure and properties of Al alloys with high Mg content

The effects of trace Sc, Zr, and Ti on the microstructure and hardness of Al alloys with high Mg content (Al-6Mg, Al-8Mg, and Al-10Mg) were studied by optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brinell hardness. The grain size of the as-cast alloys was refined by the addition of Sc and Zr, and it was further refined by the addition of Ti. With the same contents of Sc, Zr, and Ti, an increase in Mg content was beneficial to the refinement due to the solution of Mg into α-Al. The refined microstructures of the as-cast alloys were favorable for Brinell hardness. Addition of Sc, Zr, and Ti to the Al-10Mg alloy results in the improvement of peak hardness and it is about 45% higher than that of the Al-10Mg alloy, which is due to fine precipitations of Al₃(Sc_1−x Zr _x ), Al₃(Sc_1−x Ti _x ), and Al₃(Sc_1−x−y Zr _x Ti _y ).     

Effects of titanium addition on structural,mechanical, tribological,and corrosion properties of Al−25Zn−3Cu and Al−25Zn−3Cu−3Si alloys

To investigate the effect of grain refinement on the material properties of recently developed Al−25Zn−3Cu based alloys, Al−25Zn−3Cu, Al−25Zn−3Cu−0.01Ti, Al−25Zn−3Cu−3Si and Al−25Zn−3Cu−3Si−0.01Ti alloys were produced by permanent mold casting method. Microstructures of the alloys were examined by SEM. Hardness and mechanical properties of the alloys were determined by Brinell method and tensile tests, respectively. Tribological characteristics of the alloys were investigated by a ball-on-disc type test machine. Corrosion properties of the alloys were examined by an electrochemical corrosion experimental setup. It was observed that microstructure of the ternary A1−25Zn−3Cu alloy consisted of α, α+η and θ (Al₂Cu) phases. It was also observed that the addition of 3 wt.% Si to A1−25Zn−3Cu alloy resulted in the formation of silicon particles in its microstructure. The addition of 0.01 wt.% Ti to the Al−25Zn−3Cu and Al−25Zn−3Cu−3Si alloys caused a decrement in grain size by approximately 20% and 39% and an increment in hardness from HRB 130 to 137 and from HRB 141 to 156, respectively. Yield strengths of these alloys increased from 278 to 297 MPa and from 320 to 336 MPa while their tensile strengths increased from 317 to 340 MPa and from 334 to 352 MPa. Wear resistance of the alloys increased, but corrosion resistance decreased with titanium addition.     

Evolution of microstructure,hardness, and corrosion properties of high-entropy Al0.5CoCrFeNi alloy

In this study, we investigate the microstructure, hardness, and corrosion properties of as-cast Al_0.5CoCrFeNi alloy as well as Al_0.5CoCrFeNi alloys aged at temperatures of 350 °C, 500 °C, 650 °C, 800 °C, and 950 °C for 24 h. The microstructures of the various specimens are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe X-ray microanalysis (EPMA). The results show that the microstructure of as-cast Al_0.5CoCrFeNi comprises an FCC solid solution matrix and droplet-shaped phases (Al–Ni rich phases). At aging temperatures of between 350 and 950 °C, the alloy microstructure comprises an FCC + BCC solid solution with a matrix, droplet-shaped phases (Al–Ni rich phase), wall-shaped phases, and needle-shaped phases (Al–(Ni, Co, Cr, Fe) phase). The aging process induces a spinodal decomposition reaction which reduces the amount of the Al–Ni rich phase in the aged microstructure and increases the amount of the Al–(Ni, Co, Cr, Fe) phase. The hardness of the Al_0.5CoCrFeNi alloy increases after aging. The optimal hardness is obtained at aging temperatures in the range 350–800 °C, and the hardening effect decreases at higher temperatures. Both the as-cast and aged specimens are considerably corroded when immersed in a 3.5% NaCl solution because of the segregation of the Al–Ni rich phase precipitate formed in the FCC matrix. Cl^? ions preferentially attack the Al–Ni rich phase, which is a sensitive zone exhibiting an appreciable potential difference, with consequent galvanic action.     

Effect of Cr on Microstructure and Properties of a Series of AlTiCr x FeCoNiCu High-Entropy Alloys

A series of AlTiCr _x FeCoNiCu (x: molar ratio, x = 0.5, 1.0, 1.5, 2.0, 2.5) high-entropy alloys (HEAs) were prepared by vacuum arc furnace. These alloys consist of α-phase, β-phase, and γ-phase. These phases are solid solutions. The structure of α-phase and γ-phase is face-centered cubic structure and that of β-phase is body-centered cubic (BCC) structure. There are four typical cast organizations in these alloys such as petal organization (α-phase), chrysanthemum organization (α-phase + β-phase), dendrite (β-phase), and inter-dendrite (γ-phase). The solidification mode of these alloys is affected by Chromium. If γ-phase is not considered, AlTiCr_0.5FeCoNiCu and AlTiCrFeCoNiCu belong to hypoeutectic alloys; AlTiCr_1.5FeCoNiCu, AlTiCr_2.0FeCoNiCu, and AlTiCr_2.5FeCoNiCu belong to hypereutectic alloys. The cast organizations of these alloys consist of pro-eutectic phase and eutectic structure (α + β). Compact eutectic structure and a certain amount of fine β-phase with uniform distribution are useful to improve the microhardness of the HEAs. More γ-phase and the microstructure with similar volume ratio values of α-phase and β-phase improve the compressive strength and toughness of these alloys. The compressive fracture of the series of AlTiCr _x FeCoNiCu HEAs shows brittle characteristics, suggesting that these HEAs are brittle materials.     

The effect of molybdenum on the corrosion behaviour of the high-entropy alloys Co1.5CrFeNi1.5Ti0.5Mox in aqueous environments

The purpose of this study is to investigate the electrochemical properties of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x high-entropy alloys in three aqueous environments which simulate acidic, marine, and basic environments at ambient temperature (∼25 °C). The potentiodynamic polarisation curves of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x alloys, obtained in aqueous solutions of H₂SO₄ and NaOH, clearly revealed that the corrosion resistance of the Mo-free alloy was superior to that of the Mo-containing alloys. On the other hand, the lack of hysteresis in cyclic polarisation tests and SEM micrographs confirmed that the Mo-containing alloys are not susceptible to pitting corrosion in NaCl solution.     

Microstructure and wear resistance of AlCrFeNiMo0.5Six high-entropy alloy coatings prepared by laser cladding

In recent years, the coating prepared by laser cladding has attracted much attention in the field of wear research. In this work, AlCrFeNiMo_0.5Si_x (x=0, 0.5, 1.0, 1.5, 2.0) high-entropy alloy coatings were designed and prepared on Q235 steel by laser cladding. The effect of Si content on microstructure, microhardness and wear resistance of the coatings was studied in detail. The results indicate that the AlCrFeNiMo_0.5Si_x high-entropy alloy coatings show an excellent bonding between substrate and the cladding layer. The AlCrFeNiMo_0.5Si_x coatings are composed of nano-precipitated phase with BCC structure and matrix with ordered B2 structure. With the addition of Si, the white phase (Cr, Mo)₃Si with cubic structure appears in the interdendritic, and the morphology of the coating (x=2.0) transforms into lamellar eutectic-like structures. The addition of Si enhances the microhardness and significantly improves the wear resistance of the coatings. As x increases from 0 to 2.0, the average hardness of the cladding zone increases from 632 HV to 835 HV, and the wear rate decreases from 1.64×10⁻⁵ mm³·(N·m)⁻¹ to 5.13×10⁻⁶ mm³·(N·m)⁻¹. When x≥1.5, the decreasing trend of the wear rate gradually slows down. The wear rates of Si1.5 and Si2.0 coatings are 5.85×10⁻⁶ mm³·(N·m)⁻¹ and 5.13×10⁻⁶ mm³·(N·m)⁻¹, respectively, which is an order of magnitude lower than that of Q235 steel.

     

New TiC/Co1.5CrFeNi1.5Ti0.5 Cermet with Slow TiC Coarsening During Sintering

New TiC/Co_1.5CrFeNi_1.5Ti_0.5 cermet was developed by exploiting the advantages of the high-entropy alloy (HEA) binder. A much finer grain structure and thus improved hardness–toughness combination were obtained as compared with two traditional binders, Ni and Ni₁₃Mo₇. From the coarsening behavior of TiC grains, the coarsening process of TiC in these three binders is diffusion-controlled. The activation energy of TiC + 20%Co_1.5CrFeNi_1.5Ti_0.5 is the highest and that of TiC + 20%Ni is the lowest. The high activation energy of the Co_1.5CrFeNi_1.5Ti_0.5 binder was attributable to its high content of carbon-strong-binding elements, Cr and Ti, and cooperative diffusion and higher packing density of multiple different-sized atoms. Low diffusion coefficient, low surface energy of TiC grains, and low solubility of Ti in the HEA liquid explain the slow coarsening of TiC grains. This study demonstrates that Co_1.5CrFeNi_1.5Ti_0.5 is an excellent HEA binder for TiC cermets.     

Effect of 0.3% Sc on microstructure,phase composition and hardening of Al-Ca-Si eutectic alloys

The phase composition, microstructure and hardening of aluminum-based experimental alloys containing 0.3% Sc, 0–14% Si and 0–10% Ca (mass fraction) were studied. The experimental study (electron microscopy, thermal analysis and hardness measurements) was combined with Thermo-Calc software simulation for the optimization of the alloy composition. It was determined that the maximum hardening corresponded to the annealing at 300–350 °C, which was due to the precipitation of Al₃Sc nanoparticles with their further coarsening. The alloys falling into the phase region (Al)+Al₄Ca+Al₂Si₂Ca have demonstrated a significant hardening effect. The ternary eutectic (Al)+Al₄Ca+Al₂Si₂Ca had a much finer microstructure as compared to the Al–Si eutectic, which suggests a possibility of reaching higher mechanical properties as compared to commercial alloys of the A356 type. Unlike commercial alloys of the A356 type, the model alloy does not require quenching, as hardening particles are formed in the course of annealing of castings.     

Microstructure and creep behavior of directionally solidified TiAl-base alloys

Tensile creep tests were conducted on directionally solidified TiAl alloys to discern the effect of alloying and lamellar orientation. A seeding technique was used to align the TiAl/Ti₃Al lamellar structure parallel to the growth direction for alloys of Ti–47Al, Ti–46Al–0.5Si–0.5X (X=Re, W, Mo, and Cr), and Ti–46Al–1.5Mo–0.2C (at.%). Tensile creep tests were performed at 750 °C using applied stresses of 210 and 240 MPa. Aligning the lamellar microstructure greatly enhances the creep resistance which can further be improved by additional alloying.     

固溶态和挤压态Mg-xLi-3Al-2Zn-0.5Y(x=4,8,12)合金的显微组织和腐蚀行为

研究固溶态和挤压态Mg-xLi-3Al-2Zn-0.5Y(x=4,8,12,质量分数,%)合金的显微组织和腐蚀行为。结果表明,当锂含量从4%增加到12%,合金基体由α-Mg单相转变为α-Mg+β-Li双相,再转变为β-Li单相。Mg-4Li-3Al-2Zn-0.5Y和Mg-12Li-3Al-2Zn-0.5Y合金具有晶间腐蚀和点蚀的混合腐蚀特征,前者与沿晶界析出的AlLi相有关,后者与第二相与基体之间的高电位差有关。挤压态合金的耐蚀性优于固溶态合金。挤压态Mg-8Li-3Al-2Zn-0.5Y合金具有最低腐蚀速率(P_W=(0.63±0.26)mm/a),主要归因于该合金的第二相分布更均匀、通过牺牲β-Li相形成的保护性α-Mg相和相对完整的更均匀分布的氧化膜。     

Influence of Si and Ti contents on the microstructure, microhardness and performance of TiAlSi intermetallics in Al-Si-Ti alloys

In this study, the influence of Si and Ti contents on the microstructure, microhardness and morphology of TiAlSi intermetallics in ternary Al-Si-Ti alloys was investigated. The increase of Si addition in Al-xSi-2Ti alloys leads to an increase of Si content in TiAlSi phase as well as an increase of microhardness. A phase evolution from Ti(Al_1−xSi_x)₃ to Ti₇Al₅Si₁₂ at about 14 wt.% Si was detected, while all the TiAlSi intermetallics exhibit flake-like. The increase of Ti content promotes the morphological transformation of TiAlSi from flake-like to block-like and primary Si particles are replaced by blocky TiAlSi particles in hypereutectic Al-Si alloy. The high-temperature strengthening effect of TiAlSi particles in a piston alloy was investigated and the strength is increased by 11.9% in this article, while the elongation and yield strength are increased by 17.6% and 10.1%, respectively.