ENGINEERING TECHNOLOGY

Scientists have developed an ultra-high strength plastic tungsten high entropy alloy


Tungsten alloy has become an irreplaceable key material in the fields of national defense, aerospace, nuclear energy and other fields due to its high density, high strength and hard performance, and radiation resistance. With the rapid development of these high-tech fields and the complexity and extremism of the service environment, the toughness and plasticity of tungsten alloy are put forward more and more demanding requirements, breaking through the inherent strength-plastic mutual exclusion (trade-off) of materials, and developing ultra-high strength tungsten alloy with strength of 2GPa and good tensile plasticity is a challenging problem to be solved at present.

In the previous related research, Dai Lanhong’s research team of the Institute of Mechanics, Chinese Academy of Sciences, developed a tungsten high-entropy alloy with self-sharpening characteristics, which achieved a breakthrough in self-sharpening in cast tungsten alloy for the first time, and significantly improved the high-speed armor-piercing penetration ability (Acta Mater, 2020, 186: 257-266). Recently, Dai Lanhong’s research team of the Institute of Mechanics, together with the University of California, Berkeley, Beihang University, Hong Kong Polytechnic University and City University of Hong Kong, has made important progress in the research of ultra-high strength tungsten and high entropy alloy. The researchers proposed a new strategy for step-by-step controllable ordered nanoprecipitation strengthening and toughening, and successfully realized the controllable double co-lattice nanoprecipitation phase precipitation of nanosheet layered δ phase and nanoparticle γ” phase at high temperature (900°C) and medium temperature (650°C), so that the prepared tungsten high-entropy alloy material has an ultra-high room temperature strength of 2.15GPa and a tensile plasticity of 15% (Figure 3). At the same time, the tungsten high-entropy alloy can maintain a high yield strength above 1GPa at a high temperature environment of 800°C (Figure 4). Compared with the reported related tungsten alloy and refractory high-entropy alloy, the strong plasticity of the developed tungsten high-entropy alloy is at the optimal level in the world. The researchers systematically characterized and analyzed the microstructure of different tensile deformation stages, and revealed that the dislocation slip cut through the two colattice precipitation phases and maintained a perfect con-lattice structure, so as to realize the crystal structure of the material “cut through and continuous”, which is the main reason for the ultra-high plasticity of the alloy material. After the dislocation is cut δ precipitation of the sheets, the layers have significant local high strain, while maintaining the continuity of the crystal structure (Figure 5), effectively releasing the stress concentration caused by the accumulation of dislocations and avoiding the brittle damage induced by the early initiation of cracks. After the dislocation is cut through the precipitation of the colattice γ”, conlattice strengthening and ordered strengthening occur, further increasing the strength of the material (Figure 6). The synergistic strengthening and toughening of the two nanoprecipitated phases of different morphologies realizes the simultaneous improvement of the strength and plasticity of the alloy. The step-by-step controllable precipitation structure realizes the ultra-high plasticity of tungsten high-entropy alloy, which provides a new idea for the research and development of high-performance advanced alloy materials.

The research results were recently published in Nature Communications, 2023, 14, 3006 under the title “Ultra-strong tungsten refractory high entropy alloy via stepwise controllable coherent nanoprecipitations”, with doctoral student Tong Li as the first author of the paper. This research work was supported by the National Natural Science Foundation of China (NSFC) major project of “Plastic Flow and Toughening Mechanism of Disorganized Alloys”, the Basic Science Center Project of “Multiscale Problems of Nonlinear Mechanics”, and the Special Project of Class B Strategic Leading Science and Technology of the Chinese Academy of Sciences. (Source: Institute of Mechanics, Chinese Academy of Sciences)

Related paper information:https://www.nature.com/articles/s41467-023-38531-4

Figure 1. Step-by-step controllable precipitation structure evolution. a-c are schematic diagrams of structural evolution, d and c are EBSD structural representations at the corresponding stages, and f-i are the corresponding TEM structural representations.

Figure 2. Crystallographic relationship and elemental distribution of differential biphasic co-lattice precipitation and matrix. a and b are δ and γ” precipitated spherical aberration corrected TEM structural analysis, c and d are δ and γ” precipitated element distribution 3D atomic probe (3D-APT) analysis, and e and f are corresponding one-dimensional element distributions.

Figure 3. Quasi-static tensile properties at room temperature and comparison with other metals

Figure 4. High temperature quasi-static tensile properties and comparison with other metals

Figure 5. Characterization of lattice continuous TEM structure after dislocation cut δ sheets

Figure 6. Dislocation cut over γ” colattice precipitated TEM structure characterization

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