The solute segregation and its effects on the cohesion of the Fe/Y₂Ti₂O₇ interface in ferritic oxide dispersion strengthened (ODS) alloy have been investigated using first-principles calculations. The computational results indicate that W, Cr, Al, Nb, Zr, and Hf are prone to segregate to the Fe/Y₂Ti₂O₇ interface and enhance the cohesive strength of the Fe/Y₂Ti₂O₇ interface, improving its stability. He atoms exhibit a strong tendency to segregate at the Fe/Y₂Ti₂O₇ interface, leading to embrittlement of the interface. Moreover, in the case of co-existing of W, Cr, Al, Nb, Zr, and Hf with He atoms, it is found that W, Cr, and Al increase the segregation energy of He at the Fe/Y₂Ti₂O₇ interface. This promotes the diffusion of He from the Fe/Y₂Ti₂O₇ interface into the bulk of the Y₂Ti₂O₇, thereby reducing He-induced embrittlement at the Fe/Y₂Ti₂O₇ interface. Finally, the electronic structures of the Fe/Y₂Ti₂O₇ interfaces with and without solute elements, as well as the interaction between metallic solutes and He, have been discussed in detail to reveal the mechanisms of alloying reduction effect on He-segregated embrittlement at the Fe/Y₂Ti₂O₇ interface. The results obtained from this work suggest that adjusting the alloying components in ODS alloys can improve the radiation resistance of the alloy, providing theoretical guidance for the design and optimization of ferritic ODS alloys.

This study investigates the thermodynamic and mechanical properties of Y4Zr3O12 and Y2Ti2O7 oxides in ferritic alloys with and without Helium utilizing a systematic first-principles approach. Firstly, the atomic arrangement of Y and Zr atoms at cation 18f sites in δ-(Y–Zr–O) oxide is identified, while it is found that Y4Zr3O12 exhibits a more robust formation tendency than Y2Ti2O7. Furthermore, it is noted that both Y4Zr3O12 and Y2Ti2O7 oxides demonstrate a prior ability to trap Helium compared to the bcc-Fe matrix, which leads to a substantial enhancement on the stiffness of both oxides. The elastic moduli of both Y4Zr3O12 and Y2Ti2O7 oxide exhibit a gradual increase with the growing Helium concentration. As a result, the enhanced shear modulus of oxides and sustained shear modulus of the bcc-Fe matrix collectively contribute to the overall strength of ferritic alloys under Helium environments. The findings in this work propose valuable insights for guiding critical strategies in the design of high-performance oxide-dispersion-strengthened ferritic alloys, particularly for applications in Helium environments.

Statistical alloy theory based on the Master Equation approach with ab initio calculated interatomic interactions is employed to investigate the growth of precipitates at the early stages of solid solution decomposition, as well as the dissolution of small precipitates during the coarsening stage, upon simulated annealing of ternary Al–Sc–Zr alloys. We show, in agreement with previous studies, that the Zr alloying to Al–Sc alloys promotes the formation of core–shell nanoparticles whose structure is found to be very sensitive to the parameters characterizing the solute diffusion rates in the alloy. We demonstrate that the core–shell structure of precipitates slows down the dissolution of small particles, thus hampering the microstructure coarsening at elevated temperatures.

The critical role of Cr on nanoprecipitates and the mechanical property of Fe-Ni-Al-Mn ferritic steel were systematically studied in this research. The two types of nanoprecipitates in the Cr added alloy were characterized through a combination of aberration-corrected scanning transmission electron microscopy and atom probe tomography techniques. The atomic-scale structure and chemistry analysis reveal that fine globular-shaped precipitates have a B2-structure, while coarse elongated precipitates have B2+L2₁ composite structures. The first-principles calculations reveal that the segregation of Cr at the L2₁/bcc interface reduces the interface and strain energy for the nucleation of the L2₁-type phase. With the increasing precipitate size, the B2 structure is gradually transformed to L2₁ to reduce elastic strain, thereby promoting the formation of B2+L2₁ composite nanoprecipitate. The addition of 10 wt% Cr results in an increase of ∼275 MPa in yield strength without obvious loss of ductility. The effect of Cr on the strength mechanisms were quantitatively analyzed, revealing that the strength of the ferritic alloy mainly improved by the formation of B2+L2₁ composite nanoprecipitate, which is more effective than solid solution strengthening.

Ductility deterioration induced by L21-Ni2AlTi precipitates in the aged ferritic alloys was examined systematically by using a combination of scanning transmission electron microscope (STEM), mechanical tests and first-principles thermodynamic calculations. The experimental studies revealed that the strength and hardness of the aged Fe–10Cr–5Ni–1Al–1Ti ferritic alloy containing B2–NiAl and L21-Ni2AlTi precipitates were higher than that of the aged Fe–10Cr–5Ni–1Al ferritic alloy containing NiAl precipitates, whereas the elongation-to-failure decreased dramatically from 9.3% to 0.3% indicating an obvious ductility deterioration due to the formation of L21-Ni2AlTi precipitates. This was also confirmed by the observation of fracture transition mode from dimpled failure to cleavage failure. The first-principles calculations, concerning the precipitate/matrix interface, were carried out to provide a theoretical analysis for the ductile–brittle transition by means of empirical ductility criteria ratios G/B and (C12–C44)/B as well as cleavage energy. The cleavage energy results indicated an intrinsic brittleness of the L21-Ni2AlTi phase and the L21-Ni2AlTi/BCC-Fe interface. Our analysis revealed that the intrinsic brittleness of L21-Ni2AlTi phase and L21-Ni2AlTi/BCC-Fe interface plays a vital role in determining the deformation behavior of the aged Fe–10Cr–5Ni–1Al–1Ti alloy.

The distribution of solutes and their interactions play a crucial role in determining the mechanical properties of the γ/γ′ interface in Ni-based single-crystal alloys. In this study, atomic interactions between Re and W and their alloying effects on the inter-phase cohesion of the γ/γ′ interface are investigated by first-principles calculations. Our results show that W atom exhibits a preference for partitioning into the γ phase, while the stability of the γ/γ′ interface can be enhanced due to the partitioning of W to the γ′ phase. Moreover, our results reveal that partitioned W atoms in the γ′ phase contribute to the strengthening of the γ/γ′ interface. Conversely, the dissolution of W atoms in the γ phase weakens the inter-phase cohesion. However, this detrimental effect can be mitigated by introducing of Re into the γ/γ′ interface. Partitioning of Re and W into separate phases yields minimal alterations in interaction energies, resulting in a notable enhancement of inter-phase cohesion when compared to the partitioning of Re and W within γ phase of the γ/γ′ interface. Additionally, the partitioning of solute atoms at the γ/γ′ interface leads to local lattice distortion and interfacial energy reduction, which contribute to the enhancement of inter-phase cohesion of the γ/γ′ interface. As a result, a model is proposed for interpretation of crack propagation at the γ/γ′ interface at the threshold region with the presence of tensile stress in Ni-based single-crystal alloys.

Atomic interactions and phase stability in Ni-rich Ni-W alloys have been investigated by using first-principles methods and statistical thermodynamic simulations. First-principles methods have been employed to explore lattice expansion, enthalpies of formation, atomic interactions, and ordering energies of ordered as well as random structures in Ni-rich Ni-W alloys with consideration of the corresponding temperature-dependent magnetic states. It is found that atomic interactions in Ni-rich Ni-W alloys depend on alloy composition, atomic volume, and magnetic state. Nevertheless, the magnetic state of Ni greatly affects the formation enthalpies, which leads to a diverse phase separation behavior at finite temperature in Ni-rich Ni-W alloys. By using atomic interactions that reproduce the ordering energies obtained in the direct total energy calculations, our statistical thermodynamic simulations of chemical short-range order results show that fcc-based ordered D1a, D022, and Pt2Mo phases can be observed in Ni-20 at.% W, Ni-25 at.% W, and Ni-33 at.% W alloys, respectively. Moreover, the short-range order diffuse intensity and atomic stacking for aforementioned ordered phases have been analyzed, the order–disorder transition behaviors have been also investigated in detail for the Ni-rich Ni-W alloys up to 35 at.% W with comparison of current experimental results. Both magnetic state and alloy composition have the potential to induce the formation of distinct ordered phases, offering promising avenues for designing Ni-based alloys. The methodologies we used in this study can be applied to investigate the atomic interactions as well as phase stability in other alloy systems.

Ni and its alloys are susceptible to hydrogen embrittlement. In this study, we investigate the phenomenon of hydrogen-enhanced decohesion at inter-phase interfaces in precipitation-hardened Ni-based alloys using a systematic first-principles approach. We demonstrate that hydrogen atoms primarily prefer to localize at the Ni3Al phase in the Ni/Ni3Al interface, while they tend to be trapped by Ni in the Ni/Ni3Nb interface. Our findings reveal that hydrogen induces inter-phase embrittlement in both the Ni/Ni3Al and Ni/Ni3Nb interfaces. Moreover, we show that the hydrogen-enhanced decohesion at these interfaces is influenced by various factors such as hydrogen pressure, hydrogen content, temperature, and strain. Finally, we discuss in detail the hydrogen-enhanced decohesion mechanisms at the Ni/Ni3Al and Ni/Ni3Nb interfaces, including their electronic structures, energy landscape of hydrogen at trapping sites, and schematics of crack propagation.