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high-entropy, medium-entropy alloys, magnesium and aluminum

Time:2020/06/16 丨 source:未知 丨 visit count:

Professor Liu Jinchuan, Lv Jian, Lv Zhaoping, Hu Liangbing, Ritchie N/S review in the field of high-entropy, medium-entropy alloys, magnesium and aluminum alloys
 
Aluminum alloy is an alloy based on aluminum with a certain amount of other alloying elements, and is one of light metal materials. Aluminum alloy has the characteristics of low density, good mechanical properties, good processing performance, non-toxic, easy to recycle, conductivity, heat transfer and corrosion resistance. It is used in the marine industry, chemical industry, aerospace, metal packaging, transportation, etc. Widely used in the field. Magnesium alloy is an alloy composed of magnesium added with other elements. Small density, high strength, large elastic modulus, good heat dissipation, good shock absorption, greater impact load capacity than aluminum alloy, good resistance to organic and alkali corrosion. Magnesium alloys are widely used in portable equipment and the automotive industry to achieve the purpose of lightweighting. In traditional metal alloys, atoms with a small content tend to be randomly distributed below their solubility limit, and a second phase is formed above the solubility limit. The concept of multi-element alloys has recently expanded this view because these materials are single-phase solid solutions in which atoms such as metal elements are mixed. Such materials have received extensive attention because of their outstanding mechanical properties. Ternary systems are often called medium-entropy alloys, and quaternary or quaternary systems are called high-entropy alloys, implying their high configuration entropy. As an emerging structural material, medium and high entropy alloys have good comprehensive mechanical properties in structural applications. Next, we will review the research progress of Liu Jinchuan, Lv Jian, Lv Zhaoping, Hu Liangbing, Ritchie and other Daniels in the fields of high-entropy, medium-entropy alloys, magnesium, and aluminum alloys.
 
  1. Science: excellent mechanical behavior of multi-component intermetallic nanoparticles and complex alloys
 

 
The team of academician Liu Jinchuan of the City University of Hong Kong cannot overcome this difficult problem in the alloy design based on the single principal alloy system (the ability to further optimize the alloy chemistry and microstructure is limited). The metallurgical design of the multi-element alloy system recently proposed by the team is to ease These questions provide a promising path. In this study, the team developed an innovative design strategy to eliminate the ductility loss of gigapascal strength alloys. The design concept is to controllably manufacture coherently strengthened ductile multi-component intermetallic nanoparticles (MCINPs) used in the fcc-type HEA system. By controlling the order-disorder phase transition and element distribution, the nanoscale of MCINPs is achieved. The in situ extension of the precipitation. This conceptual design can not only give full play to the strengthening effect of intermetallic nanoparticles, but also maintain a high work hardening rate and plastic deformation stability. Therefore, MCINP strengthened alloy (MCINPS) has an excellent strength-ductility combination without encountering the common problems of early local necking and limited uniform ductility. This MCINP strengthened alloy has an excellent strength of 1.5 gigapascals and up to 50% ductility at ambient temperature.
 
Literature link:
http://science.sciencemag.org/content/362/6417/933
 
  1. Nature: the two-phase nanostructure casts the strongest magnesium alloy in history
 

 
The team of academician Lu Jian from the City University of Hong Kong has developed a dual-phase nanocrystalline magnesium alloy material. The MgCu2 grains with a diameter of about 6 nm are evenly embedded in a magnesium-rich amorphous shell with a thickness of about 2 nm by magnetron sputtering , Production of magnesium-based super-nano-sized dual-phase glass crystals with amorphous/nanocrystalline dual-phase structure (SNDP-GC). The dual-phase material combines and strengthens the advantages of nanocrystalline materials and amorphous nanomaterials, exhibits near ideal strength at room temperature, and solves the problem of sample size effect. The magnesium alloy system made by the research team is composed of nanocrystalline cores buried in an amorphous glass shell. The strength of the resulting dual-phase material is almost ideal 3.3 GPa, which is by far the strongest magnesium alloy film. At the same time, the researchers proposed a strength enhancement mechanism composed of a constitutive model. During the preparation of the material, a crystalline phase composed of grains with a diameter of about 6 nm and almost no dislocations was formed. When the strain occurs, the crystal The phase prevents the movement and propagation of the local shear band. In any shear band that has occurred, the embedded grains split and rotate, which is also beneficial to the material strengthening and resistance to the softening effect of the shear band.
 
Literature link:
https://www.nature.com/articles/nature21691
 
  1. Nature: 3D printing realizes high-strength aluminum alloy

 
The team of Professor John H. Martin of the University of California reported that the introduction of controlled solidification nanoparticle nucleating agents in the additive manufacturing process solved the unbearable microstructure with large columnar grains and periodic cracks caused by melting and solidification dynamics. After the nucleating agent is used, high-strength aluminum alloys that are incompatible with additive manufacturing can be successfully processed using selective laser melting, without cracks and equiaxes, achieving a fine-grain microstructure and achieving material strength equivalent to that of forged materials. This additive manufacturing method is applicable to various alloys and can be implemented using a series of 3D printers, providing a foundation for a wide range of industrial applications.
 
Literature link:
https://www.nature.com/articles/nature23894
 
  1. Science: Precipitation strengthening effect of aluminum alloy at room temperature cyclic plasticity
 

 
The team of Professor Christopher Hutchinson of Monash University in Australia reported the use of a completely new means of strengthening, namely cyclic strengthening (CS). The researchers found that controlled room temperature cyclic deformation is sufficient to continuously inject vacancies into the material and mediate the dynamic precipitation of ultrafine solute clusters to achieve the purpose of strengthening. Compared with traditional heat treatment, not only the processing time is much shorter, but also this treatment can obtain high strength and high plasticity aluminum alloy materials. The microstructure obtained using this method is also more uniform than that of traditional heat treatment, and does not show no precipitation zone. Therefore, using this method to obtain an aluminum alloy may have a stronger resistance to damage.
 
Literature link:
http://science.sciencemag.org/content/363/6430/972
 
  1. Nature: Improve the strength and ductility of high-entropy alloys through ordered oxygen complexes
 

 
Professor Lv Zhaoping's team at the University of Science and Technology Beijing reported that a new type of oxygen was found in the alloy. The team used TiZrHfNb high-entropy alloy (HEAs) as a model material, doped it with limited oxygen, and found that oxygen formed a new type of ordered oxygen complex. The state of the composite is between oxide particles and conventional random interstitials. Conventional interstitials only contribute to the strength of the alloy. However, this new composite can not only significantly increase the strength, but also ensure the ductility of the material. Further mechanical tests showed that the tensile strength of TiZrHfNb high-entropy alloy with new ordered oxygen composites increased by approximately 48.5% compared to undoped oxygen alloys, while the ductility was also greatly enhanced by 95.2%. This result breaks the law that the strength and ductility of metal materials cannot be improved at the same time, and provides new ideas for the design of high-strength-high ductility metal materials.
Literature link:
https://www.nature.com/articles/s41586-018-0685-y
 
  1. Science: a high-entropy alloy that synthesizes eight elements
 

 
The team of Professor Hu Liangbing of the University of Maryland and researchers from the University of Illinois at Chicago, Johns Hopkins University, and Massachusetts Institute of Technology introduced a mixture of precursor metal salts on a carbon carrier by thermal shock. Alloyed into single-phase solid solution nanoparticles (commonly referred to as high-entropy alloy nanoparticles (HEA-NP). The researchers synthesized by controlling carbon thermal excitation (CTS) parameters (substrate, temperature, impact duration, and heating/cooling rate) A wide range of multi-component nanoparticles with the desired chemistry (composition), size and phase (solid solution, phase separation).
 
Literature link:
https://science.sciencemag.org/content/359/6383/1489.full
 
  1. Nature: adjust the element distribution, structure and performance in high-entropy alloys through composition
 

 
The team of Professor Robert Ritchie of the University of California, Berkeley, Professor Yu Qian of Zhejiang University, and Ting Zhu of the Georgia Institute of Technology in the United States revealed the elemental distribution of several typical and new high-entropy alloys by using atomic resolution chemical mapping. The researchers first studied the CrMnFeCoNi Cantor alloy with a face-centered cubic structure. In this alloy, the distribution of the five constituent elements is relatively random and uniform. In contrast, in the new CrFeCoNiPd alloy, the palladium atoms have very different atomic sizes and electronegativity, which makes the uniformity of the alloy significantly weaker, and the five elements tend to aggregate more. In-situ TEM analysis showed that during the strain experiment, the alloy exhibited a large number of relatively early plastic deformation dislocation cross-slip, resulting in a very strong dislocation interaction. Due to the obvious fluctuation of the component distribution, this type of deformation mechanism is particularly enhanced in the new CrFeCoNiPd alloy, and directly leads to a higher yield strength of this alloy. The study believes that the method of mapping atomic scale element distribution provides new possibilities for in-depth understanding of the chemical structure of the material, and provides a basis for achieving excellent mechanical properties by adjusting the material composition.
 
Literature link:
https://www.nature.com/articles/s41586-019-1617-1
  1. Nature: short-range ordered structure and its effect on the entropy alloy in CrCoNi
 

 
The team of Professor Andrew M. Minor of the University of California, Berkeley successfully observed the short-range ordered structure in the entropy alloy of CrCoNi using energy filtering transmission electron microscopy, and found that with the increase of the short-range ordered structure, stacking faults Energy and material hardness are also increasing. These findings indicate that thermomechanical processing can change the local order state at the nanometer scale. This study provides new ideas for regulating the mechanical properties of medium-entropy/high-entropy alloys.
 
Literature link:
https://doi.org/10.1038/s41586-020-2275-z



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