轻质高熵合金的研究进展

目前以一种或两种金属元素为主元的传统轻质合金在工业应用上有诸多局限性,如铝合金室温强度低、镁合金室温塑性和耐腐蚀性差且不易加工等。2004年叶均蔚首次正式提出高熵合金概念。高熵合金概念的提出为轻质合金的发展提供了新方向。区别于传统轻质合金,轻质高熵合金具有多种主元元素且混合熵较高,往往倾向于生成简单固溶体相。且轻质高熵合金表现出四大显著效应,即热力学上的高熵效应、动力学上的缓慢扩散效应、结构上的晶格畸变效应及性能上的"鸡尾酒"效应。独特的晶体结构和特性,使得轻质高熵合金具有传统轻质合金无法比拟的优点,如高强度、高硬度、优良的高温抗氧化性和耐腐蚀性能等。综述了轻质高熵合金的研究现状,阐述了轻质高熵合金的组元设计、制备方法、微观结构及合金性能,分析了轻质高熵合金现存的问题,并对轻质高熵合金未来的发展趋势进行了展望。     

高熵非晶材料及其增材制造技术研究进展

高熵非晶合金具有独特的物理、化学和力学性能以及更好的热稳定性,因而其制备技术成为国内外重要的研究热点之一. 然而利用传统技术制备高熵非晶材料时会产生晶粒粗大及材料浪费等缺点,难以满足工艺生产需要. 而增材制造技术的精准制造和快速冷却等特点可以解决这一问题,制备出各项性能优越的高熵非晶合金. 简要介绍了高熵非晶材料的研究体系和常用制造方法,着重阐述了高熵非晶材料的断裂强度、耐腐蚀性和热稳定性的研究,对增材制造技术的工艺特征和优势,以及利用增材制造技术制备高熵非晶合金的科学难点作出了总结. 结果表明,利用增材制造技术有利于获得致密均匀的高熵非晶材料,但对于非晶相形成的解释仅限于高熵合金4大效应.最后阐述了近年来利用常用的两种增材制造手段制造高熵非晶合金的研究,并对增材制造技术制备高熵非晶材料的发展趋势提出了展望.     

高熵合金的发展及工业应用展望

高熵合金是近十几年来出现的一类新型金属材料,通常由5种或5种以上的元素以等原子比或近等原子比构成,形成以固溶体相为主的组织结构。高熵合金概念的提出,突破了传统合金的设计理念,极大拓展了合金设计的空间。由于具有大晶格畸变、高混合熵、原子缓慢扩散和"鸡尾酒"效应等多重效应,高熵合金显示出高强度、高韧性、高硬度、异常优异的低温韧性、优异的耐腐蚀和抗辐照等独特性能。通过对高熵合金目前研究现状的系统总结,探讨了高熵合金作为一种新型结构材料在核能和石油工业等多个领域极端服役条件下的应用前景,着重分析了高熵合金在钻杆接头耐磨带、抗腐蚀套管和高性能隔水管等油气开发关键构件应用的可行性。     

轻质高熵合金的研究进展

高熵合金是由多种元素以等摩尔或近等摩尔的比例混合形成的一种新型合金,较大的密度极大地限制了其应用。为了降低高熵合金的密度,出现了由Al、Li、Mg、Ti等轻质合金元素组成的轻质高熵合金,其在交通运输、航空航天领域潜在的应用前景引起了广泛关注。本文阐述了轻质高熵合金的研究现状,分析了轻质高熵合金的组元设计方法、相组成以及制备工艺,进而归纳总结了目前不同种类的轻质高熵合金的性能,包括高强度、高硬度、高温抗氧化性、耐蚀性能等。最后总结了轻质高熵合金目前存在的一些问题以及对轻质高熵合金未来的研究方向进行了展望。     

Design Fe-based Eutectic Medium-Entropy Alloys Fe_2NiCrNb_x

High-entropy alloys have attracted broad research interests due to their unique and intriguing mechanical properties. As a category of high-entropy alloys, eutectic high-entropy alloys combine the advantages of eutectic and high-entropy alloys, with excellent mechanical properties and casting properties. Some eutectic high-entropy alloys have been developed and shown exciting properties. In this paper, based on the physical metallurgy of eutectic high-entropy alloy, medium-entropy alloy Fe_2NiCrNb_x was designed. The as-cast alloy is composed of FCC and Laves phases, Nb element promotes the formation of primary Laves phase, and the hardness of the alloy increases with the increase in Nb element. Among the four alloys, the eutectic chemical composition at eutectic point is Fe_2NiCrNb_(0.34); the alloy has a good strength and plastic balance. The ultimate comprehensive strength is 2267 MPa, and the fracture strain is 30.8%. The experiment data and analyses identified the eutectic points and the excellent mechanical behavior. Moreover, the expensive Co element was replaced by Fe element. This cheap medium-entropy alloy has promising prospect in the consideration of the cost performance ratio.     

Development and Property Tuning of Refractory High-Entropy Alloys: A Review

In the past decade, multi-principal element high-entropy alloys (referred to as high-entropy alloys, HEAs) are an emerging alloy material, which has been developed rapidly and has become a research hotspot in the fi eld of metal materials. It breaks the alloy design concept of one or two principal elements in traditional alloys. It is composed of fi ve or more principal elements, and the atomic percentage (at.%) of each element is greater than 5%but not more than 35%. The high-entropy eff ect ca...     

AlCrCuFeNbxNiTi高熵合金组织与性能研究

采用电弧熔炼制备了AlCrCuFeNb_xNiTi (x = 0, 0.25, 0.5, 1.0)高熵合金,研究不同Nb含量对AlCrCuFeNb_xNiTi高熵合金显微组织和力学性能的影响。研究表明：AlCrCuFeNb_xNiTi (x = 0, 0.25, 0.5, 1.0)高熵合金物相主要包含有序FCC的L2₁相和Laves相,还有少量的BCC(A2)和FCC相;Nb元素的添加能促进Laves相的生成且对Cu元素的偏析具有一定的抑制效果;通过相判据参数计算找到了适合AlCrCuFeNb_xNiTi高熵合金的相形成判据;添加适量的Nb元素能够改善AlCrCuFeNiTi六元高熵合金的力学性能;AlCrCuFeNb_0.5NiTi 高熵合金具有较好的综合力学性能,抗压强度达到1587.4 MPa,硬度达到568.8 HV;Nb元素含量过高时会形成过多的Laves相使合金表现出过早脆化现象。     

多主元高熵合金的研究进展

多主元高熵合金突破了以1种或2种金属元素为主的传统合金的设计理念,是一种有5种以上主元且每种主元原子百分数不超过35％的新型合金。高熵合金显现出许多不同于传统合金的组织和性能特点,是一个具有学术研究价值和工业应用潜力的材料领域。本文重点介绍了高熵合金的定义、组织和性能特点与研究状况。     

Formation condition of solid solution type high-entropy alloy

Formation condition of high-entropy alloys with solid solution structure was investigated. Seventeen kinds of the high-entropy alloys with different components were prepared, the influencing factors (the comprehensive atomic radius difference δ, the mixing enthalpy ΔH and the mixing entropy ΔS) of phase composition of the alloys were calculated, and the microstructure and phase compositions of alloys were analyzed by using SEM and XRD. The result shows that only the systems with δ≤2.77 and ΔH≥?8.8 kJ/mol will form high entropy alloy with simple solid solution. Otherwise, intermetallic compounds will exist in the alloys. So, selection of the type of element has important effects on microstructure and properties of high entropy alloys.     

Thermodynamic approach to quantitative assessment of propensity of metallic melts to amorphization

On thermodynamic grounds, it was found that key properties that control the capacity of molten metallic alloys for transition into an amorphous state are the excess (configurational) entropy and heat capacity of the liquid. Chemical short-range order in liquids exhibiting various ten-dencies to glass formation was analyzed on the basis of the associated solution theory and the results of detailed thermodynamic research on a wide set of alloys. An interrelation was established between the association, characteristics of molten alloys (viscosity η, activation energies of viscous flow, and crystallization) that determine the possibility of amorphization and characteristics of glassy state stability (glass transition point, Gibbs energy, and enthalpy of crystallization). It was demonstrated that the magnitude of the key functions is completely determined by the covalent constituent of chemical interaction between components and depends mainly on the entropy terms of association reactions. The prospects for developing the quantitative criteria of amorphization on the basis of the entropy of association was discussed. It was also shown that the suggested approach based on taking into accoun the specificity of chemical interaction between components can be useful for prediction of physical, chemical, and mechanical properties of solid amorphous metallic materials.     

Phase Stability of Low-Density,Multiprincipal Component Alloys Containing Aluminum,Magnesium, and Lithium

A series of low-density, multiprincipal component alloys containing high concentrations of Al, Mg, Li, Zn, Cu and/or Sn was designed using a strategy based on high-entropy alloys (HEAs). The alloys were prepared by induction melting under high-purity argon atmosphere, and the resulting microstructures were characterized in the as-cast condition. The resulting microstructures are multiphase and complex and contain significant volume fractions of disordered solutions and intermetallic compounds. By analyzing the atomic size difference, enthalpy of mixing, entropy of mixing, electronegativity difference, and valence electron concentration among the constituent elements, modified phase formation rules are developed for low-density multiprincipal component alloys that are more restrictive than previously established limits based on more frequently studied HEAs comprising mostly transition metals. It is concluded that disordered solid solution phases are generally less stable than competing ordered compounds when formulated from low-density elements including Al, Mg, and Li.     

激光熔化沉积CrMnFeCoNi高熵合金组织和低温力学性能

采用激光熔化沉积和铸造技术分别制备了CrMnFeCoNi高熵合金。通过X射线衍射(XRD)、金相腐蚀、扫描电镜(SEM)和力学拉伸实验等分析手段对不同方法制备的CrMnFeCoNi高熵合金相组成、微观组织及力学性能进行了对比研究。结果表明:通过激光熔化沉积和铸造技术制备的CrMnFeCoNi高熵合金均为面心立方(FCC)单相固溶体结构;采用激光熔化沉积技术制备的CrMnFeCoNi高熵合金具有更为均匀的元素分布;随着温度从293 K降低到77 K,激光熔化沉积技术制备的CrMnFeCoNi高熵合金的拉伸强度与塑性分别从518 MPa、55%提升到878 MPa、95%,表现出优异的低温力学性能。     

CoCrFeNiNbx高熵合金的研究进展

近十几年来,作为一种研究热门的新型合金,高熵合金已获得了材料界广泛的关注.其中,以等原子比CoCrFeNiMn合金为原型,已报道大量力学性能优异的fcc结构的高熵合金.近几年,由于其优异的铸造成形性能与综合力学性能,共晶高熵合金也逐渐得到科研人员的重视.本工作选取CoCrFeNiNbx合金体系,以析出强化型高熵合金和共...     

A Novel,Amorphous, Non-equiatomic FeCrAlCuNiSi High-Entropy Alloy with Exceptional Corrosion Resistance and Mechanical Properties

The exceptional corrosion resistance and mechanical properties of high-entropy metallic glasses(HE-MGs) are highly desirable for diverse critical applications.However,a long-standing problem of these alloys is that their alloy design approaches are based on limited equiatomic or near-equiatomic ratios.In this study,a novel senary alloy(non-equiatomic Fe_3 Cr_2 Al_2 CuNi_4 Si_5) with amorphous structure was prepared.This alloy exhibited exceptional corrosion resistance and Vickers hardness as high as～1 150 Hv at room temperature.The processing route involved amorphous powder molding via a mechanical alloying and ultrahigh pressure consolidation technique,resulting in an optimal microstructure of amorphous structure with nanoparticles uniformly distributed in the matrix alloy.This approach can effectively inhibit the crystallization of amorphous structure,thus providing a general pathway for manufacturing next-generation non-equiatomic HE-MGs with both exceptional corrosion resistance and strength.     

高熵合金薄膜研究现状与展望

高熵合金是一种由五种或者五种以上的元素以(近)等原子比组成的新型多主元合金材料,拥有众多优异的力学、物理和电学方面的性能,引起了科技工作者的极大关注.高熵合金薄膜是一种低维度形态(微米级)的高熵合金材料,不仅展现出与块体高熵合金相似的优异性能,而且在某些性能(如硬度)上甚至优于块体高熵合金,在诸多领域里展现出良好的应用...     

Role of Various Parameters in the Formation of the Physicomechanical Properties of High-Entropy Alloys with BCC Lattices

An analysis of simple structures of the solid-solution non-ordered high-entropy alloys (HEAs) with a bcc crystal lattice has allowed us to determine the effect of various parameters on their physicomechanical properties. It was found that, as the hardness increases, the size mismatch results in a decrease in the modulus of elasticity; however, the normalized hardness characteristic increases. It has been found that, when the enthalpy of mixing of the bcc high-entropy alloys shifts to negative values, its effect on the hardness and modulus of elasticity is nonmonotonic. A formula for calculating the modulus of elasticity of high-entropy alloys with a bcc structure has been suggested that is based on the alloy composition and role of the most refractory metallic component.     

Relative effects of enthalpy and entropy on the phase stability of equiatomic high-entropy alloys

High configurational entropies have been hypothesized to stabilize solid solutions in equiatomic, multi-element alloys which have attracted much attention recently as “high-entropy” alloys with potentially interesting properties. To evaluate the usefulness of configurational entropy as a predictor of single-phase (solid solution) stability, we prepared five new equiatomic, quinary alloys by replacing individual elements one at a time in a CoCrFeMnNi alloy that was previously shown to be single-phase [1]. An implicit assumption here is that, if any one element is replaced by another, while keeping the total number of elements constant, the configurational entropy of the alloy is unchanged; therefore, the new alloys should also be single-phase. Additionally, the substitute elements that we chose, Ti for Co, Mo or V for Cr, V for Fe, and Cu for Ni, had the same room temperature crystal structure and comparable size/electronegativity as the elements being replaced to maximize solid solubility consistent with the Hume–Rothery rules. For comparison, the base CoCrFeMnNi alloy was also prepared. After three-day anneals at elevated temperatures, multiple phases were observed in all but the base CoCrFeMnNi alloy, suggesting that, by itself, configurational entropy is generally not able to override the competing driving forces that also govern phase stability. Thermodynamic analyses were carried out for each of the constituent binaries in the investigated alloys (Co–Cr, Fe–Ni, Mo–Mn, etc.). Our experimental results combined with the thermodynamic analyses suggest that, in general, enthalpy and non-configurational entropy have greater influences on phase stability in equiatomic, multi-component alloys. Only when the alloy microstructure is a single-phase, approximately ideal solid solution does the contribution of configurational entropy to the total Gibbs free energy become dominant. Thus, high configurational entropy provides a way to rationalize, after the fact, why a solid solution forms (if it forms), but it is not a useful a priori predictor of which of the so-called high-entropy alloys will form thermodynamically stable single-phase solid solutions.     

锆基非晶合金的研究进展与应用

概括了锆基非晶系的各种体系，介绍了制备锆基非晶的各种方法，综述了锆基非晶的力学性能、物理性能及抗腐蚀性能。分析了锆基非晶在晶化过程中的热稳定性和动力学，以及晶化过程中的纳米晶、准晶与组织、结构的变化，并对锆基非晶合金的应用进行了评述。     

Alloy Design Strategies and Future Trends in High-Entropy Alloys

High-entropy alloys (HEAs) are newly emerging advanced materials. In contrast to conventional alloys, HEAs contain multiple principal elements, often five or more in equimolar or near-equimolar ratios. The basic principle behind HEAs is that solid-solution phases are relatively stabilized by their significantly high entropy of mixing compared to intermetallic compounds, especially at high temperatures. This makes them feasibly synthesized, processed, analyzed, and manipulated, and as well provides many opportunities for us. There are huge numbers of possible compositions and combinations of properties in the HEA field. Wise alloy design strategies for suitable compositions and processes to fit the requirements for either academic studies or industrial applications thus become especially important. In this article, four core effects were emphasized, several misconceptions on HEAs were clarified, and several routes for future HEA research and development were suggested.     

High-entropy alloys: Interrelations between electron concentration,phase composition,lattice parameter,and properties

An analysis of more than 200 high-entropy alloys (HEA) allowed us to find interrelations between the electron concentration, phase composition, lattice parameter, and properties of solid solutions with bcc and fcc crystal lattices. Main conditions for the appearance of high-entropy chemical compounds, such as Laves, σ, and μ phases were determined. The necessary condition for the formation of 100% high-entropy σ phase is the formation of σ phase in two-component alloys for different combinations of elements, which are components of the HEA, and the electron concentration should be 6.7–7.3 electrons per atom. To form a 100% high-entropy Laves phase, the following conditions should be fulfilled: the total negative enthalpy of mixing of alloy is about –7 kJ/mol and less; the difference between the atom sizes in a pair is more than 12%; the enthalpy of the mixing of two present elements is less than –30 kJ/mol; and the average electron concentration is 6–7 electrons per atom. It was shown that the ratios of lattice parameters of solid-solution HEA, which were experimentally determined, to the lattice parameter of the most refractory metal in the HEA determine the value of the modulus of elasticity.