高熵合金的性能研究进展

Research Progress on Properties of High-Entropy Alloys

高熵合金(HEAs)是一种基于3至5种金属元素、各组元摩尔分数介于5%~35%的高合金化程度的新型材料。由于其多主元及化学无序的原子结构特点,该类合金具有优于传统合金的特殊性能,如高的强度和硬度、优异的抗腐蚀性能、良好的耐高温和抗氧化性能、优异的抗辐照及软磁性能等,在航空航天、生物制药、航海船舶等领域具有巨大的应用潜力。目前,高熵合金的研究主要以过渡族元素、轻质元素、难熔元素和稀土元素为主,研究方向集中在涂层、薄膜和制备技术等。而块体高熵合金因制备工艺受限、性能研究不完善等问题,其工程应用受到了极大的限制。本文从工程实际出发,介绍了高熵合金的定义及结构特征,主要讨论了影响块体高熵合金性能的因素如合金元素和制备工艺,综述了其高硬度和优异的耐磨性、耐腐蚀性能、热稳定性、抗辐照性能及低温性能的研究进展,并对高熵合金高温性能和抗辐照性能的研究提出了展望。

Multi-principal component high-entropy alloy(HEAs)are a new kind of material with high alloying degree.Traditonal alloys are based on long-range ordered structures,it can be toughened by introducing various disorderings or second phases,but it is still limited to select a kind of principal element.The breakthrough in HEAs is based on a traditional concept of one of the main elements,and the high entropy effect of mutil-principal component alloy is used to promote the formation of solid solution phase with simple structure,therefore HEAs show excellent performance.HEAs form crystals in most cases,and face-centered cubic(fcc)structure has good plasticity but insufficient strength,while body-centered cubic(bcc)structure has high strength and brittleness.Due to the slow diffusion of atoms in the dynamics of HEAs,amorphous phases or nanocrystals may also be formed.The design concept of HEAs meet the following three empirical criteria:5 to 5 metallic elements;the mole fraction of each element is between 5%and 35%;the mixing entropy of the HEAs is greater than 1.61R(R is the gas molar constant,which is 8.314 J·mol·K).As we get deeper into the idea of HEAs,the degree of confusion in atomic entropy is the dominant factor in defining its concept.Previous experiments found ternary and quaternary alloys tended to form simple solid solution structures which had equal or nearly equal molar ratios,and those alloys were also defined as HEAs because of their excellent comprehensive properties.The characteristics of HEAs have been summarized as four effects,which are high entropy effect,slow diffusion effect,lattice distortion effect and cocktail effect,reflected respectively in thermodynamics,dynamics,structure and performance.High entropy effect inhibites the formation of intermetallic compounds,and promotes the alloy to form simple solid solution phase.HEAs has no solute solvent discrimination and atoms occupy the lattice positions randomly,so the lattice distort and even collapse due to the difference in atomic radius,resulting in intense solid solution strengthening mechanisms.Lattice distortion accompanies the interaction between elements and limits the diffusion rate of atoms to lattice points,which is beneficial to obtain amorphous phase and nanocrystalline.Cocktail effect refers to the fact that the principal elements of a HEAs have different properties,and random combinations lead to unexpected results,so it widens the design range of HEAs components and provides more choice space.At present,HEAs are being developed rapidly in ultrahigh strength and have almost the same performance as martensitic aging steels.They are expected to replace the traditional metal structural materials,but their fracture toughness is still insufficient.In the field of high temperature,depending on the high entropy effect of thermodynamics and the hystersis diffusion effect of atoms on dynamics,HEAs are likely to break through the limit of traditional nickel-based alloy and realize the high specific strength and ductility merger at high temperature,which is expected to be used as an ideal material for engines in the field of aerospace.In addition,due to the characteristics of HEAs multi-principal component and chemical disordered atomic structure,this kind of alloy has better special properties than traditional alloys,such as high strength and hardness,excellent corrosion resistance,high temperature resistance and oxidation resistance,excellent resistance to radiation and soft magnetic properties,etc.HEAs have great application potential in aerospace,biological pharmacy,marine ships and other fields.In the early days,based on traditional group elements,people mostly studied blocky HEAs.However,its cost,density and casting size could not meet the increasing demand for production.With the rapid development of science and technology in China,the increasingly stringent working environment poses great challenges to the properties of materials,such as high temperature(>1100℃),low temperature(as low as liquid nitrogen temperature),and strong irradiation.In recent years,scholars have also studied a large number of light-weight HEAs and refractory HEAs.Despite the repulsive mixing enthalpy effect among various elements,the cocktail effect on the properties of HEAs provides more possibilities for combinations between different elements.Therefore,it is still a difficult problem to design alloy componets with high specific strength and extreme temperature resistance.At present,the research elements on HEAs are mainly focused on light elements,refractory elements and rare earth elements,so the research interests are concentrated upon coatings,thin films,and preparation technoloies.Based on engineering practice,the definition and structure characteristics of HEAs were intruduced in this paper,and the main factors affecting the properties of bulk HEAs were discussed such as alloy elements and preparation technology.The high hardness and excellent wear resistance,corrosion resistance,thermal stability,anti-irradiation performance and low temperature performance of HEAs were reviewed systematically.Finally,the research prospects of HEAs with high temperature performance and antiirradiation performance were presented.