Lightweight, refractory high-entropy alloys with excellent mechanical properties through nano-precipitation and dislocation-induced deformation are obtained. At this stage, there is a wide range of application requirements for alloys with certain mechanical properties at high tem

obtains lightweight, refractory high-entropy alloy with excellent mechanical properties through nano-precipitation and dislocation-induced deformation and obtains lightweight, refractory, high-entropy alloys with excellent mechanical properties

At this stage, there is a wide range of application demands for alloys with certain mechanical properties at high temperatures. Metal materials required by new technologies must work under conditions with higher service temperatures than nickel-based alloys. Although nickel-based alloys have a unique combination of properties at higher temperatures, these alloys either have lower room temperature ductility (less than 10%) or have higher density (more than 8.5g/cm3), which greatly limits their practical application. Recently, a lightweight, refractory high entropy alloy (RHEAs) has been developed to solve these problems, and has received widespread attention due to their good high temperature strength. Some researchers have observed that RHEAs (such as NbMoTaW and AlMo0.5NbTa0.5TiZr) show higher high-temperature mechanical properties compared with typical nickel-based alloys (such as Inconel 718 and Mar-M247), and have broad prospects for high-temperature applications. To further improve the alloy, reducing quality and improving brittleness are the top priority.

A latest study from Shenzhen University explores to regulate density and improve mechanical behavior through RHEAs components, and designs a series of Al0.5Ti2Nb1Zr1WX (X: 0, 0.3, 0.5 and 0.7), and analyzes the microstructure of the alloy, strengthening toughening mechanism, mechanical properties at room temperature and high temperatures, and potential deformation mechanism . The relevant papers are published in Materials & Design with the title "A superb mechanical behavior of newly developed lightweight and ductile Al0.5Ti2Nb1Zr1Wx refractory high entropy alloy via nano precipitates and dislocations induced-deformation".

Paper link:

https://doi.org/10.1016/j.matdes.2022.111034

Study found that different deformation characteristics were observed in Al0.5Ti2Nb1Zr1W0.5RHEA. RHEA exhibited continuous strain hardening between 973 K and 1073 K, while RHEA compressed at 1273 K showed no strain hardening and flow softening after yield. A large number of dislocations are clustered near GBs, and the concentration of dislocations in these areas helps deform near GBs. The lack of dislocation migration and diffusion at 973 K means that the stress cannot be relieved or coordinated deformation. The resulting stress concentration accelerates the generation and diffusion of microcracks, which is not conducive to the material's deformation resistance. As the strain increases, the stress concentration at GBs promotes the formation of microcracks. Meanwhile, the substructures triggered by dislocation rearrangement lead to dynamic replies, and this type of deformation accelerates the transition from hardening to softening.

Figure 1 (a, b) DF-TEM micrograph of Al0.5Ti2Nb1Zr1W0.5RHEA, corresponding SAED graph shows B2 phase; (c) HR-TEM micrograph shows the boundary between BCC/B2; (d) Al0.5Ti2Nb1Zr1Wx (X: 0-0.7) XRD graph of RHEA

Figure 2 Al0.5Ti2Nb1Zr1Wx (X: 0-0.7) Compression performance of RHEAs (a, b) Engineering/True Stress-Strain Curve at Room Temperature and (c) High Temperature/True Stress-Strain Curve

Figure 3 Al0.5Ti2Nb1Zr1W0.5RHEA compressed 60% EBSD results at 298 K, 973 K and 1273 K

Figure 4 Al0.5Ti2Nb1Zr1W0.5RHEA compressed 60% EBSD results at 298 K, 973 K and 1273 K

Figure 4 Al0.5Ti2Nb1Zr1W0.5RHEA compressed 60% EBSD results at 298 K, 973 K and 1273 K

Figure 4 Al0.5Ti2Nb1Zr1W0.5RHEA compressed 60% EBSD results at 298 K, 973 K and 1273 K

Figure 4 Al0.5Ti2Nb1Zr1W0.5RHEA compressed 60% EBSD results at 298 K, 973 K and 1273 K

Figure 4 Al0.5Ti2Nb1Zr1W0.5RHEA compressed 60% EBSD results at 298 K, 973 K and 1273 K

Figure 5 Schematic diagram of deformation mechanism after compression of Al0.5Ti2Nb1Zr1W0.5RHEA after compression at different temperatures

The newly developed lightweight Al0.5Ti2Nb1Zr1W0.5RHEA exhibits outstanding yield strength (SYS) due to its body-center cubic structure and B2 nano precipitation phase. It has high SYS (σ0.2/ρ=187MPa g-1 cm3), uniform hardening and excellent plasticity (ε68%). After compression at 1073K, excellent SYS (σ0.2/ρ=94MPa g-1 cm3) was obtained, and the strain hardening ability was provided by dislocation-dominated deformation. In contrast, the expansion and dynamic recrystallization of microcracks (DRX) accelerates the transition from hardening to softening. Compared to 973 K and 1073 K deformation RHEA, the flow stress of the RHEA dropped rapidly during compression at 1273 K, which subsequently produced steady state flow. CDRX and dislocation annihilation effectively reduce stress concentration and avoid the spread of microcracks under GBs. The diffusion-controlled DRX is the main reason for the continuous strain softening after 1273 K compression.These results not only point out that the alloy has excellent deformability and excellent high-temperature properties, but also promotes the future development and application of such alloys. (Text: Breaking the Wind)

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This article comes from the WeChat public account "Material Science and Engineering". Please contact us for reprinting. Reprinting to other websites is prohibited without permission.