Microstructure and Mechanical Properties of CoCrFeMnNiSnx High-Entropy Alloys

Metals and Materials International - The objective of this study is to investigate the effect of Sn content on the microstructure and mechanical properties of the CoCrFeMnNiSnx high entropy alloys....     

Alloy Design and Properties Optimization of High-Entropy Alloys

This article reviews the recent work on the high-entropy alloys (HEAs) in our group and others. HEAs usually contain five or more elements, and thus, the phase diagram of HEAs is often not available to be used to design the alloys. We have proposed that the parameters of ?? and ?? can be used to predict the phase formation of HEAs, namely ??????1.1 and ??????6.6%, which are required to form solid-solution phases. To test this criterion, alloys of TiZrNbMoV _x and CoCrFeNiAlNb _x were prepared. Their microstructures mainly consist of simple body-centered cubic solid solutions at low Nb contents. TiZrNbMoV _x alloys possess excellent mechanical properties. Bridgman solidification was also used to control the microstructure of the CoCrFeNiAl alloy, and its plasticity was improved to be about 30%. To our surprise, the CoCrFeNiAl HEAs exhibit no apparent ductile-to-brittle transition even when the temperatures are lowered from 298?K to 77?K.     

Microstructure and Properties of Aluminum-Containing Refractory High-Entropy Alloys

A new metallurgical strategy, high-entropy alloying (HEA), was used to explore new composition and phase spaces in the development of new refractory alloys with reduced densities and improved properties. Combining Mo, Ta, and Hf with “low-density” refractory elements (Nb, V, and Zr) and with Ti and Al produced six new refractory HEAs with densities ranging from 6.9 g/cm³ to 9.1 g/cm³. Three alloys have single-phase disordered body-centered cubic (bcc) crystal structures and three other alloys contain two bcc nanophases with very close lattice parameters. The alloys have high hardness, in the range from H _v = 4.0 GPa to 5.8 GPa, and compression yield strength, σ _0.2 = 1280 MPa to 2035 MPa, depending on the composition. Some of these refractory HEAs show considerably improved high temperature strengths relative to advanced Ni-based superalloys. Compressive ductility of all the alloys is limited at room temperature, but it improves significantly at 800°C and 1000°C.     

The Role of Compositional Tuning of the Distributed Exchange on Magnetocaloric Properties of High-Entropy Alloys

This paper explores the FeCoNiCuMn high-entropy alloy system, where small departures from equiatomic composition have yielded technologically interesting 300-K Curie temperatures (\(T_{\mathrm{c}}\)), making them promising for magnetocaloric applications. We also demonstrate that the small deviations from equiatomic compositions do not affect the structural stability of our single-phase fcc-based solid solutions. Room-temperature Mössbauer spectroscopy measurements provide evidence for the distributed exchange interactions (\(J_{\mathrm{ex}}\)) occurring between the magnetic elements, which contribute to a broadened magnetocaloric effect observed for these alloys. The average hyperfine field observed in the Mössbauer spectra decreases as the \(T_{\mathrm{c}}\) of the alloys decrease, confirming direct current magnetic measurements. Multiple peaks in the hyperfine field distribution are interpreted considering pairwise ferromagnetic or antiferromagnetic \(J_{\mathrm{ex}}\) between all elements except the Cu diluent as contributing to overall magnetic exchange in the alloy.     

AlxFeCoNiCrTi系高熵合金的组织结构及电化学性能研究

研究了不同Al含量的AkFeCoNiCrTi (x:摩尔比;x=0.5,1,1.5,2)多主元高熵合金的组织结构及其在0.5MH2SO4溶液和1 MNaCl溶液中的电化学性能,并与市售304不锈钢以及AIFeCuCoNiCrTix高熵合金进行对比.结果表明,随Al的添加,合金组织结构逐渐由FCC相和BCC相组成变为单一的BCC相.极化曲线测试结果表明,在0.5MH2SO4溶液以及1 MNaC1溶液中,该系合金耐腐蚀性要明显优于市售304不锈钢及AlFeCuCONiCrTix高熵合金,而其中AlFeCoNiCrTi合金具有最优越的综合耐腐蚀性能.     

Microstructures and Mechanical Properties of NiTiFeAlCu High-Entropy Alloys with Exceptional Nano-precipitates

Three novel NiTiFeAlCu high-entropy alloys, which consist of nano-precipitates with face-centered cubic structure and matrix with body-centered cubic structure, were fabricated to investigate microstructures and mechanical properties. With the increase in Ni and Ti contents, the strength of NiTiFeAlCu alloy is enhanced, while the plasticity of NiTiFeAlCu alloy is lowered. Plenty of dislocations can be observed in the Ni₃₂Ti₃₂Fe₁₂Al₁₂Cu₁₂ high-entropy alloy. The size of nano-precipitates decreases with the increase in Ni and Ti contents, while lattice distortion becomes more and more severe with the increase in Ni and Ti contents. The existence of nano-precipitates, dislocations and lattice distortion is responsible for the increase in the strength of NiTiFeAlCu alloy, but it has an adverse influence on the plasticity of NiTiFeAlCu alloy. Ni₂₀Ti₂₀Fe₂₀Al₂₀Cu₂₀ alloy exhibits the substantial ability of plastic deformation and a characteristic of steady flow at 850 and 1000 °C. This phenomenon is attributed to a competition between the increase in the dislocation density induced by plastic strain and the decrease in the dislocation density due to the dynamic recrystallization.     

Microstructure and Electrochemical Properties of CoCrCuFeNiNb High-Entropy Alloys Coatings

The CoCrCuFeNiNb high-entropy alloys coatings were prepared by using plasma-transferred arc cladding process. The microstructure and electrochemical behaviors of the coating were investigated in detail. The experimental results indicated that the coating consists of a simple fcc solid solution phase and an order（Co Cr）Nb-type Laves phase. The polarization curves, obtained in 1 and 6 mol/L hydrochloric acid solutions, clearly indicated that the general corrosion resistance of the coating at ambient temperature was better than that of 304 stainless steel. The coating displayed a lower corrosion current and lower corrosion rate. Electrochemical impedance spectroscopy demonstrated that the impedance of the coating was significantly higher than that of the 304 stainless steel.     

Optimizing Mechanical Properties of AlCoCrFeNiTi_x High-Entropy Alloys by Tailoring Microstructures

The effects of Ti addtions and the heat treatment on the mechanical properties of AlCoCrFeNiTix (x = 0, 0.2, 0.3, 0.4 and 0.5) high-entropy alloys (HEAs) were studied. The results show that the dendrite phase with a body-centered-cubic (bcc) structure transforms into the interdendrite phase with a new bcc structure. With the increase of the Ti contents and heat-treatment temperature, the average hardness and yield strengths are greatly improved, and the highest hardness and yielding strength are 583 HV and 2.07 GPa, respectively in the investigated HEA system. The as-cast and annealed HEAs exhibit excellent mechanical properties, combining with high yielding strength and plasticity. The solid solution strengthening mechanism of Ti additions is responsible for the strengthening effect of AlCoCrFeNiTix HEAs.     

Role of Fractal Mesostructure in the Formation of Mechanical Properties of Metals and Alloys

Metal Science and Heat Treatment -     

Effect of Aluminum Content on Microstructure and Mechanical Properties of High-Entropy AlxCoCuNiTi Alloys

Metal Science and Heat Treatment - Five-component high-entropy AlxCoCuNiTi alloys at x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 melted in a vacuum arc furnace have been studied. The effect of the aluminum...     

Kinetic Parameters of the Process of Pearlite Formation in Iron-Carbon Alloys

A physical model of formation of pearlite in eutectoid γ → α transformation, which reflects the main laws in the kinetics of the process in iron-carbon alloys, is suggested. The kinetic parameters of the process are refined. An accurate solution of the diffusion problem of formation of lamellar pearlite in iron-carbon alloys is obtained. A theoretical dependence of the rate of formation of pearlite and of the lamella-to-lamella distance on the supercooling ΔT below the eutectic temperature is suggested. The obtained dependences explain known experimental results.     

Thermal Expansion,Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory

The effects of V, Cr, and Mn on the magnetic, elastic, and thermal properties of FeCoNiCu high-entropy alloy are studied by using the exact muffin-tin orbitals method in combination with the coherent potential approximation. The calculated lattice parameters and Curie temperatures in the face-centered-cubic structure are in line with the available experimental and theoretical data. A significant change in the magnetic behavior is revealed when adding equimolar V, Cr, and Mn to the host composition. The three independent single-crystal elastic constants are computed using a finite strain technique, and the polycrystalline elasticity parameters including shear modulus, Young’s modulus, Pugh ratio, Poisson’s ratio, and elastic anisotropy are derived and discussed. The effects of temperature on the structural parameters are determined by making use of the Debye–Grüneisen model. It is found that FeCoNiCuCr possesses a slightly larger thermal expansion coefficient than do the other alloys considered here.     

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.     

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.     

凝固过程中AlCoCrFeNiTi0.5高熵合金的组织结构演变

采用反重力真空吸铸技术,制备致密且组织演变明显的AlCoCrFeNiTi0.5高熵合金,研究凝固过程中高熵合金的组织结构转变规律。结果表明:从合金的边缘到中心,随着凝固的进行,合金的组织结构发生规律性转变;边缘区域为衍射峰强度相近的bcc1相和bcc2相,之后bcc2衍射峰强度降低,在中心区域合金析出σ相;从边缘到中心,组织由细小的晶粒转变为树枝晶组织,且晶粒尺寸一直呈长大趋势,在中心区域,树枝晶间析出细小的球状σ相;随着晶粒的长大,合金的硬度降低,但中心区域由于析出σ相,虽然晶粒尺寸最大,合金具有最高的硬度。     

MgNi非晶合金的制备及电极性能的研究

用机械合金化的方法研究了MgNi非晶相的形成效率、合成物相组成和相结构的演变以及电极性能与机械球磨工艺的依赖关系。模拟电池法测量Mg-Ni合成物的电极性能,发现放电容量的大小与非晶相的形成效率成正比,球磨50～60h的MgNi非晶具有最大的放电容量,继续延长球磨时间导致放电容量下降。基于MgNi非晶相形成过程的相组成和相结构,探讨了合成物电极性能的变化规律。     

难熔高熵合金在反应堆结构材料领域的机遇与挑战

传统反应堆结构材料性能已趋于极限,亟需开发新型材料。难熔高熵合金是以多种难熔元素作为主元的新型金属材料,具有独特的力学、物理和化学性质,尤其在高温力学、抗辐照等方面表现出优异的性能。难熔高熵合金在第4代核裂变反应堆包壳材料、核聚变堆面向第一壁材料等关键领域具有广阔的应用前景。本文结合具有代表性的文献,围绕难熔高熵合金的力学性能、抗辐照性能、抗氧化性能阐述了其强化机制与抗辐照机理,梳理了难熔高熵合金的发展脉络,在此基础上展望了难熔高熵合金在反应堆结构材料领域的应用前景。     

Relationship Between the Processing Parameters and the Properties of Semi-solid Processed Al Alloys

Relationship between the processing parameters and the properties of semi-solid processed Al alloys were studied and microstructure and mechanical properties of semi-solid processed Al parts for automobile application as a function of processing parameters were compared with those of die-cast parts and forged parts. In addition, the locations for the gate during the semi-solid processing were varied to elucidate the distribution of micro-porosities and resulting mechanical properties and the T6 heat treatment on the semi-solid processed part was performed so that the effect of heat treatment on the improvement of mechanical properties could be evaluated in terms of tensile strength, wear properties, etc. Microstructure of semi-solid processed Al part did not show any noticeable micro pores as compared to the microstructure of die-cast part. T6 heat treatment on A319 alloys has greatly improved the hardness as well as the wear resistance. Semi-solid processed A319 part showed slightly higher hardness val     

块体Fe-B-Si-Zr玻璃态合金的形成和软磁性能

添加Ｚｒ能够有效地提高某些铁基合金的玻璃态形成能力 ,因此 ,进一步研究了添加Ｚｒ的 (Ｆｅ0 75Ｂ0 1 5Ｓｉ0 1 ) 1 0 0 -ｘＺｒｘ 系块体玻璃态合金的形成能力、玻璃态合金的热稳定性和软磁性能。研究用的合金试样是采用纯金属铁、锆和晶体硼及高纯硅配成的混合料在氩气氛中电弧熔炼首先制得合金铸锭。合金锭重熔后用铜模铸造法制备成直径 1ｍｍ至 3ｍｍ的棒状试样 ,同时也用熔体旋淬法制备横截面为 0 0 2× 1 2ｍｍ2 的薄带试样。采用Ｘ射线衍射法和光学显微镜研究了试样的玻璃态组织结构 ;用差示扫描量热法研究试样与玻璃转…