Microstructure and Mechanical Properties of Al25 − xCr25 + 0.5xFe25Ni25 + 0.5x (x = 19, 17, 15 at%) Multi‐Component Alloys

A series of Al_{25 ? x}Cr_{25 + 0.5x}Fe₂₅Ni_{25 + 0.5x} (x = 19, 17, 15 at%) multi‐component alloys are prepared by arc‐melting and rapid solidification of copper molds. The technique of thermal‐mechanical processing is further applied to the master alloys to improve their mechanical properties. These alloys consist of face‐centered cubic (FCC) and body‐centered cubic (BCC) structure. The volume fraction of the BCC phase increases as Al content increase and Cr and Ni contents decrease, accompanied with a microstructural evolution from dendritic structure to lamella‐like structure. Due to the increase of volume fraction of BCC phase, the master alloys exhibit an increased strength and a declined ductility as Al content increases. The rapid solidified alloys have more BCC phase compared with the master alloys, which enhances the strength and decreases the ductility. After homogenization, hot‐rolling, and annealing at 1000 °C, the Al₈Cr_33.5Fe₂₅Ni_33.5 alloy displays excellent combination of strength (yield strength is ～635 MPa and fracture strength is ～1155 MPa) and ductility (tension strain is ～11%).

     

Strengthening Mechanisms in Bulk FeCoCrNiAl x (x=0, 0.5, 1.0) High-Entropy Alloys Fabricated by Laser Melting Deposition

Herein, FeCoCrNiAl _x (x = 0, 0.5, 1.0) high-entropy alloys (HEAs) are fabricated by the laser melting deposition (LMD) technique. With the increase of Al content, the LMD-ed microstructure transitions from a single face-centered cubic (FCC) phase to a dual-phase structure containing a small amount of body-centered cubic (BCC) phase (5.3%), and the proportion of the final BCC phase increases significantly to 98.2%. In addition to the compression tests, four strengthening models are used to evaluate the theoretical strength of the three alloys. The addition of Al element as grain refiner can improve the ultimate compressive strength of HEAs; however, the yield strength and plasticity do not improve, as theoretically expected. The FCC phase with more slip systems leads to higher plasticity in the LMD-ed FeCoCrNi HEA but results in lower yield strength. The LMD-ed FeCoCrNiAl_0.5 HEA exhibits the best combination of strength and plasticity. Therefore, to meet the required service requirements, the content of Al in the FeCoCrNiAl _x HEA should be carefully controlled under the premise of considering the actual working conditions.     

Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

The MoNbTaTiV refractory high-entropy alloy(RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying(MA) and spark plasma sintering(SPS).The microstructural evolutions,mechanical properties and strengthening mechanisms of the alloys were systematically investigated.The nanocrystalline mechanically alloyed powders with simple bodycentered cubic(BCC) phase were obtained after 40 h MA process.Afterward,the powders were sintered using SPS in the temperature range from 1500 ℃ to 1700 ℃.The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic(FCC) precipitation phases.The bulk alloy sintered at 1600℃ had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm,exhibiting outstanding micro-hardness of 542 HV,compressive yield strength of 2208 MPa,fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature.The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening.It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.     

Microstructure,thermodynamics and compressive properties of AlCrCuNiZrx (x = 0,1) high-entropy alloys

Two high-entropy alloys (HEAs), AlCrCuNiZr_x (x?=?0,1), were prepared by arc melting. The AlCrCuNi alloy consists of a face centered cubic (FCC) phase, a body centered cubic (BCC) phase and an eutectic phase, while the AlCrCuNiZr alloy contains a FCC phase, a BCC phase and an intermetallic phase. The traditional thermodynamic parameters of HEAs were converted into thermodynamic-parameter-functions of composition variable x, including ΔG_mix(x), ΔH_mix(x), ΔS_mix(x), Ω(x), δ(x),Δχ(x) and VEC(x). The thermodynamic-parameter-curves could be obtained through thermodynamic-parameter-functions via Matlab. The thermodynamics of the two alloys were analysed using the thermodynamic-parameter-curves of the AlCrCuNiZr_x (x∈[0 1]) alloys. The addition of Zr to AlCrCuNiZr favours the formation of intermetallic compound, enhances the yield strength, compressive strength and Vickers hardness, but degrades ultimate strain.     

Development of novel CoCu0.5FeNiVTix (x = 0, 0.5, 1, 1.5, 2) high-entropy alloys

CoCu_0.5FeNiVTi_x (x?=?0, 0.5, 1, 1.5, 2) high-entropy alloys (HEAs) were prepared using vacuum arc melting. The microstructures, crystal structures, hardness, compressive properties and wear resistances of the alloys were studied. The alloys always contained face-centred cubic (FCC) and body-centred cubic (BCC) solid solution regardless of the increase in Ti content. The microstructure of alloys exhibited typical dendritic characteristics, which were more and more unapparent with the increase in the Ti content. The alloys with a high content of Ti had a high compressive strength and low ductility. Owing to the formation of nano-precipitates and BCC as the major phase, the CoCu_0.5FeNiVTi₁ alloy exhibited the highest compressive strength of 2747?MPa and a plastic strain limit of 7.4%. As the content of Ti was increased, the wear resistance of CoCu_0.5FeNiVTi_x alloys displayed a rapid increase and reached the highest value when x?=?1, and finally decreased. Because of the large volume fraction of BCC, the CoCu_0.5FeNiVTi₁ alloy exhibited high hardness so exhibiting the best wear resistance. Adhesive wear and abrasive wear dominated the wear behaviour of CoCu_0.5FeNiVTi_x alloys during sliding against SUJ2 steel.     

Composition and phase structure dependence of mechanical and magnetic properties for AlCoCuFeNix high entropy alloys

In this study, the effects of composition and phase constitution on the mechanical properties and magnetic performance of AlCoCuFeNi_x (x = 0.5, 0.8, 1.0, 1.5, 2.0, 3.0 in molar ratio) high entropy alloys (HEAs) were investigated. The results show that Ni element could lead to the evolution from face centered cubic (FCC), body centered cubic (BCC) and ordered BCC coexisting phase structure to a single FCC phase. The change of phase constitution enhances the plasticity but reduces the hardness and strength. One of the interesting points is the excellent soft magnetic properties of AlCoCuFeNi_x HEAs. Soft magnetic performance is dependent on composition and phase transition. AlCoCuFeNi_1.5 alloy, achieving a better balance of mechanical and magnetic properties, could be applied as structure materials and soft magnetic materials (SMMs). High Curie temperature (>900 K) and strong phase stability below 1350 K of AlCoCuFeNi_0.5 alloy confirm its practicability in a high-temperature environment. Atomic size difference (δ) is utilized as the critical parameter to explain the lattice strain and phase transformation induced by Ni addition.     

Influence of Y on the phase composition and mechanical properties of as-extruded Mg–Zn–Y–Zr magnesium alloys

The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg–6Zn–xY–0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg₃YZn₆), face-centred cubic structure W-phase (Mg₃Y₂Zn₃) and a long period stacking ordered (LPSO) X-phase (Mg₁₂YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg–Zn–Y–Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg–Zn–Y phases have different strengthening and toughening effects on the Mg–Zn–Y–Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn₂.     

Effect of vanadium addition on the microstructure and properties of AlCoCrFeNi high entropy alloy

The purpose of this study is to investigate the effects of vanadium addition on the microstructure and mechanical properties of AlCoCrFeNiV_x (x values in molar ratio, x = 0, 0.2, 0.5, 0.8, 1.0) alloys. All the alloys were found to display a crystalline structure of simple body centered cubic (BCC). For AlCoCrFeNi and AlCoCrFeNiV_0.2 alloys, Cr and Fe elements segregated to the center of grain while Al and Ni elements segregated to the rest areas. With the increase of V content exceeding to x = 0.5, the homogenized polycrystalline grain can be obtained. For AlCoCrFeNiV_0.2 alloy, the compressive strength and plastic strain were as high as 3297.8 MPa and 26.8%, respectively, which were rare in high entropy alloys to date. The fine nanoscale spinodal decomposition microstructure was a key factor for the high fracture strength of AlCoCrFeNiV_0.2 alloy. The values of Vickers hardness increased from HV534 to HV648.8 with the increase of V content. The solid-solution strengthening of the body centered cubic matrix was found as the main factor that strengthened the alloys. With the increase of V contents from x = 0 to x = 1.0, the transformation of ferromagnetic behavior to paramagnetic behavior takes place.     

Solid state synthesis of amorphous and/or nanocrystalline Al40Zr40Si20 alloy by mechanical alloying

Mechanical alloying of Al₄₀Zr₄₀Si₂₀ powder blend has been carried out in a high-energy shaker ball mill up to 50 h. Microstructural evolution at different stages of milling has been characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). During milling, elemental Zr seems to undergo a HCP→FCC polymorphic transformation that is closely related to grain refinement and plastic strain. On the other hand, nanocrystallization and mutual dissolution of the elemental blend lead to partial solid state amorphization and development of a composite microstructure comprising of varying proportion of an amorphous phase and nanocrystalline FCC-Zr based solid solution by appropriate hours of milling. In general, the present results compare well with that from our earlier studies on mechanical alloying of Al₄₀Nb₄₀Si₂₀ and mechanical milling of elemental Zr, respectively.     

Comparison of the structure and properties of equiatomic and non-equiatomic multicomponent alloys

A series of equiatomic and non-equiatomic Fex(NiCrCo)_100?x (at.-%, x?=?25, 45, 55, 65, 75 and 85) multicomponent alloys were prepared and studied. With the increase in x, the phase structure of the alloys evolves from a single FCC phase (x?=?25, 45 and 55), to a mixture of FCC and BCC phases (x?=?55) and finally to a single BCC phase (x?=?65 and 75). As a result, the BCC-structured alloys have much higher strength and hardness than the FCC-structured alloys. The existing VEC criteria are unable to predict the FCC-BCC phase transition in these alloys.     

Mechanical alloying and spark plasma sintering of CoCrFeNiMnAl high-entropy alloy

An equiatomic CoCrFeNiMnAl high-entropy alloy was synthesized by mechanical alloying, and alloying behaviors, microstructure and annealing behaviors were investigated. It was found that a solid solution with refined microstructure of 20 nm in grain size could be obtained after 30 h milling. As-milled powder transformed into a face-centered cubic phase above 500 °C. The as-milled powder was subsequently consolidated by spark plasma sintering at 800 °C, BCC phase and FCC phase coexisted in the consolidated HEA, which had excellent properties in Vickers hardness of 662 HV and compressive strength of 2142 MPa.     

Microstructure,phase stability and properties of CoCr0.5CuxFeyMoNi compositionally complex alloys

Liquid-phase separation occurred in CoCrCu_xFeMoNi (x?≥?0.5) alloys when the mixing entropies are positive in our previous work. So in this work, CoCr_0.5Cu_xFe_yMoNi alloys are designed to investigate the microstructure, component phases and properties. FCC and BCC were detected in CoCr_0.5Cu_xFe_yMoNi alloys, accompanied with a topologically close-packed μ phase. A parameter, V_R, was defined, where V_R is the ratio of the volume fraction of BCC plus μ phases and that of FCC phase. The maximum strength and the ductility were obtained at the minimum V_R of the alloys, whereas the hardness increased with the increasing V_R. It can be presumed that the strange balance between strength, ductility and hardness is an indirect result of the degree of brittle failure.     

Microstructure and microhardness of high entropy alloys with Zn addition: AlCoFeNiZn and AlCoFeNiMoTiZn

High entropy alloys were designed from equiatomic multicomponent systems using powder metallurgy including mechanical alloying and sintering. The structure and morphology of the resulting alloys were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy techniques and their hardness values were also determined in the Vickers scale. The results indicate under the milling conditions used, the AlCoFeNiZn, AlCoFeNiMoTi and AlCoFeNiMoTiZn alloys crystallized forming BCC structures whereas the AlCoFeNi alloy presented two different phases, one with FCC structure and the other one with BCC. The synthesis method resulted in alloys with grain sizes in the nano scale having values between 4.1 and 9.4 nm on the powder form up to 40.1 nm after sintering phenomenon which lead to phase transformations which were more evident in the Mo-containing alloys. In addition, the AlCoFeNiZn and AlCoFeNiMoTiZn alloys did not show Zn traces after sintering as it was suggested by chemical analyses using energy dispersive spectroscopy, suggesting it is lost by evaporation during sintering process. Mo-containing systems exhibited the highest microhardness in both milled and sintered conditions.     

Microstructural phase evaluation of high-nitrogen Fe–Cr–Mn alloy powders synthesized by the mechanical alloying process

In this study, the formation of Fe18Cr8MnxN alloys by mechanical alloying (MA) of the elemental powder mixtures was investigated by running the milling process under nitrogen and argon gas atmospheres. The effect of the milling atmosphere on the microstructure and phase contents of the as-milled powders was evaluated by X-ray diffraction and transmission electron microscopy. The thermal behavior of the alloyed powders was also studied by differential scanning calorimetry. The results revealed that in the samples milled under nitrogen, three different phases, namely ferrite (α), austenite (γ), and a considerable amount of amorphous phase are present in the microstructure. In contrast, in the samples milled under argon, the structure contains the dominant crystalline ferrite phase. By progression of MA under the nitrogen atmosphere, the ferrite-to-austenite phase transformation occurs; meanwhile, the quantity and stability of the amorphous phase increase, becoming the dominant phase after 72 h and approaching 83.7 wt% within 144 h. The quantitative results also showed that by increasing the milling time, grain refinement occurs more significantly under the nitrogen atmosphere. It was realized that the infused nitrogen atoms enhance the grain refinement phenomenon and act as the main cause of the amorphization and α-to-γ phase transformation during MA. It was also found out that the dissolved nitrogen atoms suppress the crystallization of the amorphous phase during the heating cycle, thereby improving the thermal stability of the amorphous phase.     

元素Cu对Cu_xAlFeNiCrTi(x=0,0.5,1.0)高熵合金组织性能的影响

高熵合金具有许多优异性能,目前对其研究还不够深入。利用真空电弧熔炼炉制备了Cu_xAlFeNiCrTi(x=0,0.5,1.0)高熵合金,并通过X射线衍射仪(XRD)、扫描电镜(SEM)、显微硬度计和磨损试验对该高熵合金的微观组织及其性能进行了一系列测试,探究不同含量的Cu元素对合金性能的影响。结果表明:合金组织为树枝晶,主要是由体心立方(BCC)相和面心立方(FCC)相组成;随着Cu元素含量的增加,FCC相含量也在增加,合金的硬度降低;随Cu元素含量的增加,合金的摩擦系数减小,磨损失重和磨损体积增大,即合金耐磨性降低。     

A study of the microstructure, phase composition, and mechanical properties of extruded Mg–9Er–6Y–xZn–0.6Zr magnesium alloys

The microstructure, phase composition, and mechanical properties of Mg–9Er–6Y–xZn–0.6Zr (x = 1, 3, 5 wt%; nominal chemical composition) series alloys were investigated through optical microscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, and tensile tests. Numerous granular Mg₂₄(Er, Y, Zn)₅ phases were distributed in a discontinuous network mainly along the grain boundaries in the alloy with 1 wt% Zn. With increasing Zn content, the Mg₂₄(Er, Y, Zn)₅ phases in the alloys gradually disappeared, the amount of block Mg₁₂Zn(Y, Er) phases increased, and the block size became larger. In addition, a few lamellar phases grew parallel with one another from the grain boundaries to the grain interior in the alloys. The crystallographic structures of the Mg₁₂Zn(Y, Er) and Mg₂₄(Er, Y, Zn)₅ phases were confirmed as 18R-type long-period stacking ordered structures and body-centered cubic structures, respectively. The Mg₁₂Zn(Y, Er) phases with long-period stacking ordered structures increased the strength and toughness of the alloys more than the Mg₂₄(Er, Y, Zn)₅ phases with body-centered cubic structures.     

Elemental effect on formation of solid solution phase in CoCrFeNiX and CoCuFeNiX (X = Ti,Zn, Si,Al) high entropy alloys

The paper aims to investigate the effect of elements addition, its enthalpy of mixing, crystal structure and atomic size difference on the formation of solid solution phase during the synthesis of high entropy alloy (HEA) by mechanical alloying. For this CoCrFeNiX and CoCuFeNiX (where X?=?Ti, Zn, Si, Al), alloys were prepared by mechanical alloying. The phases formed during mechanical alloying were characterised by X-ray diffraction analysis, transmission electron microscopy and differential scanning calorimetry. Titanium and Aluminium addition facilitate solid solution formation during mechanical alloying. Formation of a BCC and FCC solid solution phase was observed for CoCrFeNiX and CoCuFeNiX system (where X?=?Ti, Al), respectively. Single solid solution phase was not observed for CoCrFeNiZn, CoCrFeNiSi, CoCuFeNiZn and CoCuFeNiSi HEA up to 20?hours of milling.     

Structure and magnetic properties of nanocrystalline mechanically alloyed Fe–10% Ni and Fe–20% Ni

The mechanical alloying technique has been used to prepare nanocrystalline Fe–10 and Fe–20 wt.% Ni alloys from powder mixtures. The structure and magnetic properties were studied by using X-ray diffraction and hysteresis measurements, respectively. For both alloys studied, a disordered body centered cubic solid solution forms after 24 h milling time. The higher the milling time, the larger the lattice parameter. The steady-state grain size is ≈10 nm. The reduction of the grain size increases the saturation magnetization and decreases the coercivity. Nanocrystalline Fe–10 and Fe–20 wt.% Ni have been shown to exhibit a soft magnetic behavior.     

Microstructure,mechanical properties and yield asymmetry of Mg–4Al–2Sn–xY alloys

The effect of 0, 0.3, 0.6, 0.9?wt-% Y addition on the microstructure and mechanical properties of extruded Mg–4Al–2Sn alloys were investigated. The results show that α-Mg, Mg₁₇Al₁₂, Mg₂Sn and Al₂Y phases form in the extruded Y-containing alloys. Mg₁₇Al₁₂ phase, containing trace amounts of Y, tends to distribute on the grain boundaries in the form of needles. When the Y content is 0.6?wt-%, the alloy has the best combination mechanical properties. Its tensile yield strength, ultimate tensile strength and tensile elongation are 172?MPa, 270?MPa and 11.2%, respectively. As the Y content increases, the tensile and compressive asymmetries in the Mg–4Al–2Sn–xY alloy decrease, due to grain refinement and the weakening of texture.     

Tailoring mechanical and magnetic properties of AlCoCrFeNi high-entropy alloy via phase transformation

Phase constitutions,either changed by alloying or by phase transformation,are the key factors to determine the magnetic and mechanical performances of high-entropy alloys (HEAs).Using the AlCoCrFeNi HEA as a candidate alloy,this paper demonstrates the effect of phase transformation on both the mechanical and magnetic properties in the multi-phase system.With increasing heat treatment temperature,the sigma (σ) and face-centered-cubic (FCC) phases disappeared at 1000 ℃ and 1200 ℃,respectively.Such volume fraction changes ofσ,FCC and body-centered-cubic (BCC) phases have divergent effects on mechanical and magnetic properties.The excellent strength-ductility combination will be achieved as the disappearance of σ phase and formation of FCC phase.As for the magnetic properties,the volume fraction of BCC phase plays a major role in determining its saturation magnetization.When the volume fraction change of BCC phase is not evident,the higher volume fraction of FCC phase will influence its magnetization at 2 T.Our present work might provide insights into analyzing the evolution of both mechanical and magnetic properties of HEAs caused by complex phase transformation.