Relationship between the unique microstructures and behaviors of high-entropy alloys

High-entropy alloys(HEAs),which were introduced as a pioneering concept in 2004,have captured the keen interest of nu-merous researchers.Entropy,in this context,can be perceived as representing disorder and randomness.By contrast,elemental composi-tions within alloy systems occupy specific structural sites in space,a concept referred to as structure.In accordance with Shannon entropy,structure is analogous to information.Generally,the arrangement of atoms within a material,termed its structure,plays a pivotal role in dictating its properties.In addition to expanding the array of options for alloy composites,HEAs afford ample opportunities for diverse structural designs.The profound influence of distinct structural features on the exceptional behaviors of alloys is underscored by numer-ous examples.These features include remarkably high fracture strength with excellent ductility,antiballistic capability,exceptional radi-ation resistance,and corrosion resistance.In this paper,we delve into various unique material structures and properties while elucidating the intricate relationship between structure and performance.

Data driving design of high-entropy alloys for lightweight and dynamic applications

The topic of high-entropy alloys is one of the focus for both physics and materials research.High-entropy alloys were usually defined as solid solution alloys,while the solid solution is different from the traditional terminal solid solution,because the solid solution without solvent element is the dominant one.The discovery of high-entropy alloys greatly extended the composition space and the possibility of creating unique micro-and nano-level structures,which can meet the demands of lightweight and dynamic applications.The relationship between the phases and the parameters for the high-entropy alloys is rather complex.The data driving design can screen the specific high-entropy alloys.The correlation between the composition and properties of highentropy alloys can be discovered by material genetic engineering and data science.

Fe-15Mn-5Si-14Cr-0.2C非晶钢微观组织与腐蚀行为

采用水冷铜坩埚磁悬浮熔炼-铜模负压吸铸法制备了Fe-15Mn-5Si-14Cr-0.2C非晶复合材料棒状试样,通过XRD和EBSD对合金的微观组织进行表征,并研究试样室温压缩力学性能;采用电化学工作站三电极体系测试试样在人工海水中的腐蚀行为,并利用SEM和EDS观察和分析电化学腐蚀后的形貌及腐蚀产物。结果表明,Fe-15Mn-5Si-14Cr-0.2C非晶复合材料试样组织由非晶相+晶体相(CFe15.1过冷奥氏体相和Fe-Cr铁素体相)组成,试样在室温环境下的综合力学性能优异,屈服强度、断裂强度和塑性应变分别为978 MPa、2645 MPa和35.8%。试样在人工海水中表现出良好的耐蚀性,与304不锈钢相比,Fe-15Mn-5Si-14Cr-0.2C非晶复合材料自腐蚀电位大,自腐蚀电流密度低,极化电阻高,容抗弧半径大且只有一个高频容抗弧,只受电极电位的影响,腐蚀的动力学速率低,钝化膜稳定致密,具有成为新一代海洋工程耐蚀材料的潜力。

Microstructures and mechanical behavior of the bimetallic additively-manufactured structure(BAMS)of austenitic stainless steel and Inconel 625

Bimetallic additively manufactured structures(BAMSs)can replace traditionally-fabricated functionallygraded-components through fusion welding processes and can eliminate locally-deteriorated mechanical properties arising from post-processing.The present work fabricates a BAMS by sequentially depositing the austenitic stainless-steel and Inconel625 using a gas-metal-arc-welding(GMAW)-based wire+arc additive manufacturing(WAAM)system.Elemental mapping shows a smooth compositional transition at the interface without any segregation.Both materials being the face-center-cubic(FCC)austenite,the electron backscattered diffraction(EBSD)analysis of the interface shows the smooth and cross-interfacecrystallographic growth of long-elongated grains in the<001>direction.The hardness values were within the range of 220-240 HV for both materials without a large deviation at the interface.Due to the controlled thermal history,mechanical testing yielded a consistent result with the ultimate tensile strength and elongation of 600 MPa and 40%,respectively,with the failure location on the stainless-steel side.This study demonstrates that WAAM has the potential to fabricate BAMS with controlled properties.

Ti-Zr-Hf-Nb-Ta-Sn high-entropy alloys with good properties as potential biomaterials

(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(100-x)Sn_(x)(x=3,5,and 7;at%)high-entropy alloys(HEAs)with good mechanical properties,corrosion resistance,and biocompatibility were developed as potential biomaterials.The effects of Sn additions on the microstructure and properties of the HEAs were investigated.The(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(100-x)Sn_(x) with x=3 at%exhibited the single body-centered-cubic(BCC)structure.The HEAs with the further increased Sn contents of x=5 at%and 7 at%were composed of a BCC phase and a hexagonal-close-packed(HCP)-(Sn,Zr)ordered phase.The addition of Sn improved the compres-sive yield strengths and hardness of the HEAs to 1068-1259 MPa and HV 315-HV 390,respectively.These HEAs also possessed relatively low Young's moduli of 80-91 GPa.Among the present Ti-Zr-Hf-Nb-Ta-Sn HEAs,the(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))97Sn3 HEA exhibited the good combination of high yield strength of~1068 MPa,relatively low Young's modulus of 80 GPa,and good plasticity(~45%).The HEAs also possess good bio-corrosion resistance and biocompatibility,parallel to the Ti-6Al-4V alloy.The Ti-Zr-Hf-Nb-Ta-Sn HEAs with the integration of the high yield strength,relatively low Young's modulus,and good corrosion resistance and bio-compatibility are promising for biomedical applications.

Chemical-element-distribution-mediated deformation partitioning and its control mechanical behavior in high-entropy alloys

The chemical element distributions always strongly affect the deformation mechanisms and mechanical properties of alloying materials.However,the detailed atomic origin still remains unknown in highentropy alloys(HEAs)with a stable random solid solution.Here,considering the effect of elemental fluctuation distribution,the deformation behavior and mechanical response of the widely-studied equimolar random Co Cr Fe Mn Ni HEA are investigated by atomic simulations combined with machine learning and micro-pillar compression experiments.The elemental anisotropy factor is proposed,and then used to evaluate the chemical element distribution.The experimental and simulation results show that the local variations of chemical compositions exist and play a critical role in the deformation partitioning and mechanical properties.The high strength and good plasticity of HEAs are obtained via tuning the chemical element distributions,and the optimal elemental anisotropy factor ranges from 2.9 to 3 using machine learning.This trend can be attributed to the cooperative mechanisms depending on the local variational composition:massive partial dislocation multiplication at an initial stage of plastic deformation,and the inhibition of localized shear banding via the nucleation of deformation twinning at a later stage.Using the new insights gained here,it would be possible to create new metallic alloys with superior properties through thermal-mechanical treatment to tailoring the chemical element distribution.

Entropy versus enthalpy in hexagonal-close-packed highentropy alloys

The addition of hexagonal-close-packed(hcp)non-rare-earth elements Zr,Ti and Co,to the 10-component hep rare-earth-based high-entropy alloys(HEAs)with a composition of ScYLaNdGdTbDyHoErLuX(X=Zr,Co and Ti)was investigated.The enthalpy of mixing between elements was found to have a significant effect on the formation of phases.The addition of Co combines with elements that had a strong chemical affinity to form intermetallic compounds by the effect of enthalpy.Ti was added with all elements with poor chemical affinity and exhibited rejection to form a phase alone.These were the two terminal manifestations of the role of enthalpy over entropy.Part of Zr was soluble in the matrix under the action of entropy,while the other part had a greater affinity for Sc than the other elements to form a precipitate under the action of enthalpy.This was the result of the local balance between the effect of enthalpy and entropy.The solid solution of the elements had different degrees of strengthening effect,among which Zr had the most excellent strengthening effect from 185 to 355 MPa,so the solid solution strengthening model and precipitation strengthening model were proposed to predict the strength of the alloy with the addition of Zr effectively.

Stress-controlled fatigue of HfNbTaTiZr high-entropy alloy and associated deformation and fracture mechanisms

The stress-controlled fatigue tests are carried out at a stress ratio of 0.1 and a frequency of 10 Hz,and span both low-cycle and high-cycle regimes by varying the applied stress amplitudes.The high-cycle fa-tigue regime gives a fatigue strength of 497 MPa and a fatigue ratio of 0.44.At equivalent conditions,the alloy’s fatigue strength is greater than all other high-entropy alloys(HEAs)with reported high-cycle fatigue data,dilute body-centered cubic alloys,and many structural alloys such as steels,titanium al-loys,and aluminum alloys.Through in-depth analyses of crack-propagation trajectories,fracture-surface morphologies and deformation plasticity by means of various microstructural analysis techniques and theoretical frameworks,the alloy’s remarkable fatigue resistance is attributed to delayed crack initiation in the high-cycle regime,which is achieved by retarding the formation of localized persistent slip bands,and its good resistance to crack propagation in the low-cycle regime,which is accomplished by intrin-sic toughening backed up by extrinsic toughening.Moreover,the stochastic nature of the fatigue data is neatly captured with a 2-parameter Weibull model.

Effect of Magnetic Field Configuration on Stray-Crystal Formation with Different Platform Sizes during Directional Solidification of Single-Crystal Superalloy

The magnetic field is an effective means to control the solidification structure and the defects of metal and semiconductor crystals.This work investigates the effects of Cusp magnetic field(CMF)and longitudinal magnetic field(LMF)on the stray-crystal formation in the platform regions during the directional solidification of single-crystal superalloy with the different cross section sizes.The application of CMF reduces the formation of platform stray-crystal,while LMF increases its generation.As the platform size increases,the stray-crystal ratio increases regardless of whether the magnetic fields are applied or not,the effectiveness of CMF increases,while that of LMF decreases.The reason that the effects of CMF and LMF on the platform stray-crystal formation could be attributed to the change of flow structure from the distribution characteristics of the thermoelectric magnetic force and the magnetic damping force near the liquid-solid interface.