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Directed energy deposition (DED) provides the possibility of high-throughput synthesis by controlling the multi-channel powder feeders. However, the compositional accuracy of the targeted alloy is of concern due to the difficulty of adjusting the proportions. In this work, we present a method to improve the adjustment accuracy of the high-throughput DED technology by replacing the elemental powder with pre-alloyed powder, and binary Al–Mn alloys with different compositions were synthesized with a composition step of 1 wt.%. The effect of Mn content on the microstructure and mechanical properties of the alloys was characterized and analyzed, and the relationship between the Al6Mn phase and the yield strength was established. The results showed that the microstructures of DED-ed Al–Mn alloys are composed of Al and Al6Mn phases with Mn contents in the range of 2–10 wt.%. The Al–Mn alloy reaches a tensile strength of 165 MPa and maintains an elongation of 9% at Mn content of 4 wt.%. The improved controlling accuracy of composition step to 1 wt.% by pre-alloyed powder in this work provides a paradigm for high-throughput discovery of high-performance alloys. [ABSTRACT FROM AUTHOR]

The preparation of transmission electron microscopy (TEM) samples is a critical step in the characterization of materials, and the focused ion beam (FIB) technique is a commonly used method. However, a significant limitation of this technique is the FIB-induced damages on the foil surfaces, which can obscure the real features of interest, particularly in radiation effects studies. To overcome this limitation, this study presents a detailed description of the flash electropolishing technique, which can be used to remove the FIB damage from samples. The flash electropolishing technique has been successfully applied to a range of materials, including Fe, Fe-based model alloys, commercial Fe-Cr alloys, and advanced Fe-Cr alloys, both in their as-received and ion-irradiated states. Furthermore, the parameters used for Fe-Cr model alloys can be adjusted for commercial and advanced alloys with minimal modifications. The study also examined the effects of electropolishing variables, such as perchloric acid concentration, electropolishing temperature, Cr concentration, and voltage. Qualitatively, a general trend and scoping test strategy is explored in our experiments. Overall, the flash electropolishing technique offers a promising solution to the challenges posed by FIB-induced damages in the preparation of TEM samples. STEM-BF of Fe-8Cr irradiated at 10−4 dpa/s and 450 °C to 0.35 dpa. The irradiation-induced small dots in the right micrograph are revealed after flash electropolishing, which are fully masked by the FIB damages in the left micrograph. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Thirteen alloys including high- and low-strength nickel-base alloys, austenitic stainless steels, and ferritic alloys were irradiated using 2 MeV protons to a damage level of 2.5 dpa at 360 °C and assessed for their susceptibility to irradiation assisted stress corrosion cracking (IASCC) in both BWR normal water chemistry (NWC) and PWR primary water. Cracking susceptibility was highest for high strength nickel-base alloys, followed by the low strength nickel-base alloys and then the low strength iron-base alloys. Cracking in the nickel-based alloys was worst in normal water chemistry, which was reversed for the iron-based alloys. In general, cracking correlated with the degree of microstructure changes, though no single feature could be linked to cracking. IGSCC occurred in both the unirradiated and irradiated conditions in high strength nickel-base alloys with susceptibility being considerably higher following irradiation. In all cases, slip was planar, and the degree of slip localization correlated with the probability of IG crack initiation. Low strength nickel-base alloys showed the same dependence on environment as high strength alloys but were considerably less susceptible to IASCC initiation. Among the low strength iron-base alloys, alloy 800 was most susceptible to IASCC initiation in both BWR NWC and PWR primary water, which also correlated with grain boundary chromium depletion and silicon segregation. Across all alloys, cracking correlated with both the degree of localized deformation and the hardness in the irradiated condition. The agreement is expected as increased hardening also correlates with localized deformation, which is likely a necessary, though insufficient condition for cracking. [ABSTRACT FROM AUTHOR]

Twelve commercial-grade austenitic alloys based on the Ni-Cr-Mo-Fe quaternary system were irradiated using 2 MeV protons at 360 °C to a damage level of 2.5 displacements per atom (dpa). Long-range ordered (Pt 2 Mo-type) precipitation under proton irradiation was observed, for the first time, in alloys C22, 625, 625P, 625D, 725, and 690. No relevant short-range ordering was observed. These irradiation-enhanced long-range ordered precipitates are coherent with the matrix despite their irregular shape. Of the potential influences on long-range ordering (Ni:Cr, and Ni:(Cr + Mo) ratios, Mo, and iron concentration), Fe content was the strongest by far. The volume fraction of LRO decreases with increasing Fe content by virtue of its role as a stabilizer of the disordered FCC phase, thus reducing the energy savings from ordering. The observed effects of Fe on long-range ordering show qualitative agreement with predictions from thermodynamic modeling. Although solid state diffusion kinetics dominate long-range ordering under purely thermal conditions, ordering under irradiation here (∼ 2.5dpa) is controlled by the thermodynamic driving force. Proton irradiation thus offers a unique approach for studying the low temperature phase transformation in a thermodynamically favored, but kinetically constrained condition. [ABSTRACT FROM AUTHOR]

The intergranular attack near both stagnant and active stress corrosion crack (SCC) tips of solution annealed alloy 690 were characterized after constant extension rate tensile tests in simulated pressurized water reactor (PWR) primary water containing 18 cc H 2 /kg H 2 O. In both cracks, an intergranular oxide, composed of NiO and Cr 2 O 3 , was observed beyond the crack tip with an adjacent Cr depleted grain boundary migration zone. The stagnant crack has a compact Cr 2 O 3 covering the crack tip and the adjacent grain boundary migration zone is deep and free of oxidation, while the active crack has porous penetrative oxide extending into the migration zone. The ability to form a compact Cr 2 O 3 film at the crack tip is important to the IGSCC resistance and may be dictated by the efficiency of Cr diffusion up the migrated grain boundary. When a compact Cr 2 O 3 film does not form at the crack tip, the Cr depleted grain boundary migration zone is subject to penetrative oxidation via the inward diffusion of oxygen, making the zone susceptible to crack propagation. Thus, even a high Cr content cannot guarantee the immunity of a Ni base alloy to SCC during dynamic straining. [ABSTRACT FROM AUTHOR]

The oxide film formed on alloy 690 in simulated pressurized water reactor primary water is decorated with NiFe 2 O 4 particles which remain epitaxial with matrix. The penetrative inner oxides on both surface and crack wall are composed of Cr-rich (Fe,Cr,Ni) 3 O 4 and Cr 2 O 3 which were formed by solid state reactions of substrate with inwards diffusing oxygen and have orientation relationships with the substrate. Cr 2 O 3 forms first along the widely spaced planes of substrate. Compact Cr 2 O 3 layer cannot develop as there is no long-range outward diffusion of Cr in substrate with low defect density at low temperature. [ABSTRACT FROM AUTHOR]

A uranium-10 wt% molybdenum (U10Mo) alloy is one of the primary candidates for metallic fuels that would use low-enriched uranium in place of highly enriched uranium, to support nuclear nonproliferation efforts. Optimal performance of a U-based metallic nuclear fuel can be achieved by retaining the high-temperature, body-centered cubic (bcc) allotrope (γ-U) at room temperature, which can be accomplished in the U10Mo alloy. However, presence of minor alloying elements can influence the final constitution of room-temperature phases in the U10Mo alloy, specifically, formation of α-U phase which results in anisotropic behavior of the fuel in reactor. Through a detailed transmission electron microscopy analysis, the present study reports the constituent phases that are present in a U10Mo alloy containing ~0.1 wt% Si after it is subjected to homogenization heat treatment and thermomechanical processing. For comparison, results from an undoped U10Mo alloy are also included. The experimental results reveal that γ-UMo solid solution is the major phase in a hot-rolled, Si-doped U10Mo alloy metallic fuel foil, along with U 2 MoSi 2 C, UC, and U 2 Mo, after isothermal annealing at 460 °C for 10 h. In contrast, after the same heat treatment, the undoped U10Mo alloy metallic fuel had formed a noticeable amount of α-U along prior γ-UMo grain boundaries through discontinuous precipitation (DP, area fraction: ~27.9 %) with characteristic lamellar morphology, together with γ-UMo, UC, and U 2 Mo. This result indicates that doping with Si could mitigate the DP reaction in U10Mo alloy and prevent formation of undesirable α-U. This work sheds light on optimizing Si-doping–dominated microstructure in U10Mo fuels and facilitates designing and tuning of microstructures of U10Mo alloys for tailoring the final designed performance of the fuel under irradiation. • Major phases in Si-doped homogenized U-10Mo sample include γ-UMo, U 2 Mo, UC, and U 2 MoSi 2 C. • After hot rolling, U 2 Mo, UC, and U 2 MoSi 2 C are there with a few α-U and UO 2 nanoparticles detected at GBs. • The area fraction of DP zones in undoped, hot-rolled U-10Mo is ~30%. Major phases after DP in hot-rolled undoped U-10Mo are γ-UMo, α-U, UC, and U 2 Mo. • Si preferentially segregates at the α-U lamellae/γ-UMo interfaces rather than at the γ΄-U 2 Mo/γ-UMo interface, and retards DP-based eutectoid transformation. [ABSTRACT FROM AUTHOR]

The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, MgZn intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Introduces novel FeNi-based alloys strengthened with multicomponent L1 2 -type precipitates containing Palladium (Pd), significantly boosting strength while preserving ductility. • Achieved an eightfold yield strength increase in FeNi-based alloys with novel Pd-containing precipitates, maintaining over 10 % ductility. • Pd addition to L1 2 precipitates modifies thermodynamic stability, morphology, coherency, and strengthening effects, offering advanced alloy design pathways. • Discovered that Pd incorporation changes precipitate shapes from spherical to acicular, reducing interface mismatch and enhancing material performance. • Demonstrated the dual role of Pd in precipitate nucleation and shear modulus anisotropy elimination, informing new alloy designs. Precipitation strengthening stands as a paramount strategy for enhancing the mechanical properties of FeNi-based alloys. Conventional precipitates used for strengthening typically contain only two major constituent elements selected from Ni, Al, and Ti. However, knowledge about the intrinsic properties and strengthening mechanisms of multicomponent precipitates remains limited. Here, we propose introducing novel multicomponent L1 2 -type precipitates containing palladium (Pd) to strengthen FeNi-based alloys. The strengthened FeNi alloy achieves an eightfold increase in strength compared to the FeNi matrix while maintaining good ductility. Using meticulous micro-characterization and energy-dispersive X-ray spectroscopy (EDS) techniques, in conjunction with first-principles calculations, this study investigated the effects of Pd addition on the thermodynamic stability, morphology, coherency, and strengthening mechanisms of the precipitates. Results indicate that the addition of Pd induces the nucleation of L1 2 -type precipitates, increases their ductility, and eliminates anisotropy in the shear modulus of the precipitates. Excessive Pd content can alter the shape of precipitates from spherical to acicular due to increased interfacial mismatch between the precipitates and the FeNi matrix. These insights shed light on the impact of Pd addition on the intrinsic properties of L1 2 -type precipitates, offering a promising pathway for the design of advanced FeNi-based alloys with optimized mechanical performance. [ABSTRACT FROM AUTHOR]

High-strength aluminium alloys attract continuous research interest, owing to their wide use in aerospace and terrestrial transportation industries. The performance of the alloys is essentially determined by nanoscale precipitates, thus understanding the structure and formation mechanism of the precipitates during thermal processing is of great importance. Here, we reveal complementary domain structures in precipitates in a high-strength Al-Zn-Mg-Cu alloy using a combination of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. Through the transfer of fivefold symmetry polyhedra at domain boundaries, the intermediate precipitates develop two sets of highly ordered and structurally complementary nanoscale domains in their nucleation and growth. This new type of atom packing maintains the topologically close-packed structure inside the precipitates while reducing the lattice misfit with the Al matrix and the barrier of structural transformations on two interfaces, demonstrating good thermal stability. Our discoveries lead to insight into the precipitate evolution in the Al-Zn-Mg-Cu alloy system and can help understand other precipitation processes of complex structured phases. Furthermore, the evolution process demonstrates an advanced mode of building metastable architectures with nanoscale interlocking pieces in alloy matrixes, which may inspire strategies to obtain high-strength, lightweight and thermostable alloys. • Precipitates in a high-strength Al-Zn-Mg-Cu alloy show complementary domain structures. • Domain structures reduce lattice misfit and barrier of structural transformations. • Precipitates maintain topologically close-packed structure and thermal stability. [ABSTRACT FROM AUTHOR]

Nb alloy has become a promising material in aerospace due to high melting point, low density and excellent processing properties. Nevertheless, the mismatched mechanical properties and thermal stability of single-phase BCC-Nb made the aircraft unable to resist cyclic vibration loads under the action of heat/force/flow. Here, after solid solution, quenching and two-stage aging, an FCC/BCC dual-phase Nb alloy with a discontinuous grain boundary (GB) carbide network skeleton was formed. The results show that interstitial C atoms precipitate from BCC-Nb matrix resulting in volume shrinkage and form discontinuous carbide at GB, which stimulates the phase transition of BCC expansion to FCC near GB. Wherein, discontinuous GB carbides help pin the GB and dislocations, impede grain growth, and change the deformation from local to the entire network skeleton. Meanwhile, the gap provides a channel for the dislocation to pass through the GB. Additionally, the FCC provides the multi-slip system to transfer the dislocation. The results show that the yield strength, tensile strength, elongation, fracture toughness and elastic modulus of Nb alloy are increased by 79.99 %, 34.52 %, 164.22 %, 204.76 % and 1.27 %, respectively. This unique microstructure is expected to guide the design of the next generation of high-performance Nb alloys. [ABSTRACT FROM AUTHOR]

Designing dual-phase titanium (Ti) alloys with exceptional damage tolerance holds profound scientific and engineering significance. A comprehensive understanding of microstructure evolution around cracks under diverse loading conditions is pivotal in advancing this pursuit. Here, tensile and fatigue cracks were formed quasi in-situ in a dual-phase Ti alloy, and the microstructures around the cracks were systematically analyzed and compared using TEM. Our findings reveal that the deflection of tensile cracks is primarily influenced by the hindrance posed by the straight α/β heterointerfaces and is further facilitated by the β -to- α" martensite transformation within the β matrix. In contrast, fatigue cracks exhibit deflection within the β matrix, located far from the α lamellae. Furthermore, the presence of spindle-shaped short α lamellae holds promise for enhancing resistance to fatigue crack nucleation. These results contribute to fundamental comprehension of the crack nucleation and propagation in dual-phase Ti alloys and provide valuable guidance for materials design. [Display omitted] [ABSTRACT FROM AUTHOR]

The chemical short-range order (CSRO) in a face-centered cubic equiatomic NiCoFeCrMn high-entropy alloy was revealed directly from advanced transmission electron microscopy in this work. Further, instead of controlling CSRO by conventional heat treatment, we show a new possibility of tailoring CSRO by radiation. The multiple types of atoms in such high-entropy system are more prone to form CSRO under radiation compared to that only under thermodynamic equilibrium conditions, due to the rearrangement of the chemical ordering during the non-equilibrium thermal spike period and the radiation-enhanced diffusion mechanism. Our results show an increase in the fraction of CSRO area by ∼45% after high-temperature irradiation with a dose of 50 DPA. Accordingly, we demonstrated that enhanced CSRO can be achieved by controlling the irradiation dose and temperature, which provides a new route to explore the kinetic evolution and effect of CSRO in complex alloy systems. [Display omitted] [ABSTRACT FROM AUTHOR]

A large variety of mechanical properties have been achieved in a single-phase CoFeNi 2 V 0.5 Mo 0.2 high entropy alloy (HEA) with various thermo-mechanical treatments. The HEA always exhibits an excellent strength-ductility synergy after different annealing processes. In particular, the material with fully recrystallized microstructure displays a yield strength of 485 MPa and a high ductility of over 60%, superior to most conventional alloys and HEAs. Results of microstructural analysis indicate that the dislocation dominated deformation mechanism involving dislocation multiplication and interactions through successive planar slip and cross slip serves to enhance the strain hardening capacity, which delays the fracture of the alloy and contributes to the excellent strength and ductility combination. Image 1 • A vast variety of mechanical properties has been achieved in CoFeNi 2 V 0.5 Mo 0.2 HEA by thermo-mechanical processing. • The dislocation dominated deformation mechanism serves to increase the strain hardening capacity. • The alloy can perform well at room temperature and elevated temperatures, which enlarges the application range of the HEAs. • A larger Hall-Petch coefficient of 688 MPa·μm1/2 indicates a more effective hardening strategy by grain refinement. [ABSTRACT FROM AUTHOR]