The development of high-entropy alloys (HEAs) has greatly stimulated alloy design strategies. By merging multiple principal elements into a simple solid solution, HEAs are caused to appear disordered at the atomic level. Studies have found that most of the special properties of HEAs are related to their disordered chemical structure, and disordered alloys, including HEAs, are generally less strong at high temperatures, which greatly limits their application. On the other hand, L12 type ordered intermetallic compounds have higher strength and are often used as reinforcing components of conventional superalloys. L12 reinforced superalloy exhibits excellent mechanical and chemical properties at high temperatures (above 750 °C) and has been widely used in gas turbines, supercritical power plants and diesel engines. Combining the advantages of HEAs and L12 ordered intermetallic compounds, L12 precipitation-enhanced HEAs has been developed and exhibits excellent strength-ductility synergies, making it a promising structural material for a variety of applications. In L12-reinforced HEAs, the reinforcement effect is strongly dependent on the deformation behavior of the phase composition and the precipitated phase. Due to the complex composition of the HEA matrix, the L12 precipitation phase introduced also exhibits a change in composition. The precipitation mechanism and deformation mechanism of the L12 intermetallic precipitation phase are still unclear, which limits the further development of L12 precipitation-enhanced HEAs.
Researchers at the City University of Hong Kong explored the location preference and deformation mechanism of L12-type multicomponent intermetallic compounds (MCIs). The paper was published in Acta Materialia under the title "Elemental partitions and deformation mechanisms of L12-type multicomponent intermetallics."
Thesis Link:
https://doi.org/10.1016/j.actamat.2021.117238
This article selects the (Ni, Co, Fe) 3 (Al, Ti, Fe) alloy as the model system. For such a system with a partially disordered structure, the key is to elucidate the role of each alloying element in the reinforcement and deformation mechanisms. Therefore, six compounds derived from (Ni, Co, Fe) 3 (Al, Ti, Fe) were also analyzed, including (Ni, Co) 3Al, (Ni, Fe) 3Al-Fe13, (Ni, Fe) 3Al-Fe7, Ni3 (Al,Ti), Ni3 (Al,Fe)-Fe13, Ni3 (Al,Fe)-Fe7.
The study found that Ti tends to occupy the Al sublattice, while the Co and Fe atoms are mainly distributed in the Ni sublattice. Construct special quasi-random structures based on established element allocation trends. The deformation mechanism of these MCIs is studied by DFT calculations, and the general plane layer fault energy is obtained, including gamma SPF and γUPF. Geometry and electronic structure analysis shows that TiAl plays an important role in improving the performance of planar faults, as TiAl reduces the adaptability of MCI to planar faults. In contrast, Co and Ni reduce the gamma SPF of MCIs by improving adaptability. The adaptability of FeNi and FeAl to planar faults has some changes, and has little effect on gamma SPF changes.
Fig. 1 Structural models of perfect L12 ordered Ni3Al (primitive), inverting boundary (APB), complex stratigraphic fault (CSF), and superlattice intrinsic fault (SISF).
Figure 2(a-e) relative energy, (f-j) 1NN, and (k-o) 2NN SRO parameters as a result of increasing DFT-MC steps
Figure 3 (a) Stable and unstable planar layer fault energy (γSF and γUPF) of APB, CSF and SISF in Ni3Al. (b) Atomic trajectories of APB, CSF and SISF general planar faults
Figure 4 considers the distribution of APB, CSF, and SISF energies (γSPF, upper row) and their means (lower rows) of MCIs
Figure 5 Trend of gamma SPF concentrations of different components in fault zones
Based on first-principles calculations, the elemental allocation and deformation mechanisms of multicomponent intermetallic compounds of the important reinforced components (Ni, Co, Fe) 3 (Al, Ti, Fe) in multicomponent HEAs were studied. To elucidate the role of each alloying element, (Ni, Co, Fe)3 (Al, Ti, Fe) and its derived six L12 subsystems were analyzed. The DFT-MC simulation results show that the geometric and electronic structural changes introduced by the APB and CSF layers are limited to the vicinity of the fault. The formation of SISF mitigates the geometry of the overall structure and the degree of redistribution of charge density. By determining the influence of different elements and different intermetallic compounds on the local geometry and electronic structure of MCIs, this paper clarifies the basic understanding of the deformation behavior of MCIs, paving the way for rational design and orderly precipitation of enhanced HEAs. (Text: Breaking the Wind)
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