Intermetallics最新文献

A complex concentrated alloy (CCA) with a nominal composition of Al_0.35CoCrFeNi (mol.%) was prepared by vacuum induction melting and tilt casting. The microstructure of the alloy in the as-cast state consists of columnar dendritic grains. The ingots were solution annealed, rotary swaged, and heat treated to obtain a uniform fine-grain structure. To study the behavior of recrystallization and grain growth, heat treatment was carried out at temperatures from 1150 °C to 1300 °C and holding times up to 480 min. The resulting microstructures were analyzed by LM, SEM, TEM, EBSD, and XRD methods followed by a comparison with the results of hardness measurements. The alloy has a thermally stable single-phase face-centered cubic (FCC) structure in the studied temperature range. The grain growth kinetics were analyzed using classical models, and the activation energy was estimated to be ∼458 kJ mol⁻¹ using an Arrhenius-type equation. The greatest resistance to grain growth was observed at a temperature of 1150 °C. Hardness tests demonstrated an almost double increase in hardness after swaging and a sharp drop during the following heat treatment due to the onset of recrystallization. The Hall-Petch hardening coefficient was calculated to be ∼277.5 HV μm^−1/2.

Ti₂AlNb alloy, as a highly promising superalloy in the aerospace field, is limited by inferior workability due to centimeter-grade coarse grains formed through casting. An in-depth understanding of the relationship between deformation heterogeneities and recrystallization kinetics of the matrix B2 phase is critical to refine and optimize its microstructure. Plane strain compression followed by heat treatment, microstructure characterizations, and full-field crystal plasticity simulations were conducted. The research found that uniform primary-slips existed in most regions of the alloy. These regions exhibited negligible deformation stored energy and misorientation, and therefore, recrystallization cannot occur after heating. The observed slip transfer at grain boundaries with good geometric alignment also indicates the difficulty in dislocation pileup as the potential recrystallization site. Three typical band-like structures, i.e., transition band, slip-interlacing band, and shear band, formed by intersection and localization of slips, possessed high deformation stored energy. Cell-like substructures readily developed in the first two regions with intersecting slips, rather than in the shear band with parallel slips. As a result, many subgrains and unclosed boundaries were formed in the first two types of bands within grains after heating due to the significant recovery effect. These multilevel deformation heterogeneities were found to be strongly associated with the dislocation structure of the alloy. TEM observations found the dissociation of dislocations with narrow widths, which enhances dislocation mobility. Consequently, the primary-slip characteristic can be maintained at a relatively large deformation, and slip transfer can occur at grain boundaries where a good geometric alignment exists.

In this study, Al₂O₃/TiAl composites were synthesized via powder metallurgy by incorporating TiO₂ nanoparticles and nanofibers as oxygen sources into Ti-45Al-8Nb pre-alloy powders, followed by vacuum hot-pressing sintering to form in-situ Al₂O₃ particles as reinforcements. The addition of TiO₂ nanofibers results in a better grain refinement effect and a more uniform distribution of Al₂O₃ particles within the composites. High-temperature tensile testing revealed that the composites prepared using TiO₂ nanofibers exhibited slightly higher strengths and significantly improved ductility compared to those synthesized with TiO₂ nanoparticles. This work not only introduces a novel additive for fabricating high-performance in-situ Al₂O₃/TiAl composites but also demonstrates a unique application of TiO₂ nanofibers.

The article describes how substitution of chromium by copper affects phase equilibria in Fe–Ni–Co–Cr high-entropy alloy. The alloys with copper content ranging from 0 to 20 % (at.) of Cu were prepared. The alloys were equilibrated at 900, 800, 700, and 650 °C. The samples were investigated by electron microscopy, EDX spectroscopy, and EBSD method. The face-centred cubic phases have only occurred in equilibrated alloys: austenite matrix, copper-rich FCC(Cu) phase, and regions containing these phases. The compositions of equilibrated samples at annealing temperatures are given. Fine microstructures including a semicoherent FCC phase rich in Cu and an FCC phase including the main magnetic elements (Fe, Co, Ni) were formed. The experimental results were compared with the calculated phase equilibria obtained by the CALPHAD method.

As cast (CrCoNi)₉₆V₄ medium entropy alloy（MEA）was prepared by vacuum arc melting. The MEA is deformed by rolling at room temperature with a total deformation of 67 %, The yield strength and tensile strength of the deformed MEA are 1297 MPa and 1410 MPa respectively, the elongation of the alloy is only 8 %.Then the deformed MEA was annealed for 30min at 700 °C, 800 °C and 900 °C respectively. The results show that the strength and ductility of the MEA after annealing were well balanced. The yield strength and tensile strength of the MEA after annealing at 900 °C/30 min are 678 MPa and 1024 MPa, and the elongation is maintained at 26 %. After annealing, a large number of annealing twins were formed in the MEA, which makes the strength and ductility of the MEA significantly improved. At the same time, Cr-rich particles were found in the MEA, which had positive effect on the improvement of the strength and ductility of the alloy.

Aiming at serious oxidation problem of 254SMO super-austenitic stainless steel during hot working, the influence of B and Ce composite microalloying on its oxidation behavior was comparatively investigated at 1050 and 1100 °C. The results demonstrated that the combination of B and Ce can significantly alter the composition of the oxide film in 254SMO. Particularly, B and Ce composite microalloying can effectively promote the diffusion of Cr to the surface, and form a dense Cr₂O₃ oxide film at a faster rate in the initial stage, which is more conducive to inhibiting the Mo volatilization and thus improving the oxidation resistance of 254SMO steels. Additionally, compared to the 0.005 wt% B (50B) and 0.005 wt% B together with 0.002 wt% Ce (50B + 20Ce) samples, the addition of 0.005 wt% B together with 0.005 wt% Ce (50B + 50Ce) had a more significant effect on improving high-temperature oxidation resistance of 254SMO. This research provides a valuable scholarly reference for improving the oxidation resistance of super-austenite stainless steels.

Traditional powder consolidation methods for fabricating metallic matrix composites often require high temperatures, high pressures, and substantial energy consumption. Therefore, developing new processing technologies that can manufacture composites rapidly, efficiently, and economically is crucial. This study introduces ultrasonic powder consolidation process as a novel strategy for fabricating and tuning metallic glass (MG) and aluminum alloy composites. By optimizing the mass ratios of Zr₅₅Cu₃₀Ni₅Al₁₀ (at.%) MG to Al-6061 powders, a diverse range of composites with tailored compressive strength and plasticity was achieved. Mechanical testing showed that increasing the aluminum content improved plasticity while maintaining significant strength. Notably, the composite with a 5:5 mass ratio exhibited the best balance of mechanical properties. Morphological characterizations demonstrated excellent densification and uniformity in the composites, with no visible defects and relative densities ranging from approximately 92 %–99 %. Detailed microstructural analysis revealed the formation of a well-bonded interface with a diffusion layer, confirming the metallurgical bonding was facilitated by ultrasonic vibration. Furthermore, the ultrasonic consolidation process enabled the successful fabrication of complex shapes, such as star and gear components, demonstrating the method's potential for advanced manufacturing. These results show that the ultrasonic powder consolidation process is a viable and efficient approach for producing high-quality MG/Al-6061 composites with enhanced mechanical performance and application versatility.

Although low levels of vanadium-doping can enhance the friction stress and strength of L1₂-nanoparticles strengthened medium-entropy alloys (MEA), how high concentrations of vanadium affect the weldability, microstructure, mechanical properties, and fracture behavior remains unknown. In this work, we designed a vanadium-doped, L1₂-nanoparticle-strengthened MEA Ni_41.4Co_23.3Cr_23.3Al₃Ti₃V₆ (at.%), which showed a high fracture toughness of 238 MPa × m^1/2, a high friction stress of 410 MPa, and a Hall-Petch strengthening coefficient of 782 MPa × μm^1/2. Pieces of the HEA were joined using electron-beam welding (EBW). Strong yet ductile defect-free joints were produced which had coarse columnar grains (88 μm) with a {110}<001> texture in the fusion zone, which was larger than the equiaxed grains in the heat-affected zones (14.9 μm) which had strong {110}<001> and relatively weak {110}<112> texture. In contrast, the base materials had fine grains (2.2 μm) with a strong {110}<111> and a relatively weak {110}<112> texture. The EBWed MEA showed a high yield strength of 599 MPa, a high ultimate tensile strength of 939 MPa, a good fracture strain of 20 %, and a fracture toughness of 198 MPa × m^1/2, which were 75 %, 83 %, 58 %, and 83 %, respectively, of the values of for the thermo-mechanically treated counterpart. The reduced strength arose from the coarse columnar grains, while the reduced fracture strain and fracture toughness could be ascribed to the reduced deformation twinning and the absence of annealing twins, which produced a poor strain hardening capability. The EBWed MEA exhibited abundant dislocation networks, indicating that a high concentration of vanadium inhibited the occurrence of stacking faults and nanoscale deformation twins.

A novel CCA was designed by substituting Nb in (FCC + C14 Laves) CoCrFeNi_2.1(Nb)_0.2 CCA by (Hf + Nb + Ta). The (HfNbTa)_0.2 CCA was homogenized, heavily cold-rolled, and isothermally annealed at 800 °C and 1000 °C for different time intervals. The (HfNbTa)_0.2 alloy revealed the presence of a Hf and Ni enriched cubic C15 Laves phase. The considerations of site occupancy behavior, formation energy, and highly off-stoichiometric composition stabilized the (Hf, Ni) rich cubic C15 Laves phase. In contrast to the brittle hexagonal C14 Laves phase in (Nb)_0.2 CCA, the C15 Laves phase in (HfNbTa)_0.2 CCA showed exceptional deformability owing to the high propensity for nano-twin formation. Meanwhile, the FCC matrix developed a deformation-induced nano-lamellar structure with a spacing of ∼45 nm. Annealing resulted in ultrafine recrystallized FCC matrix and precipitation of DO₁₉ structured ε nano-precipitates. The isothermal grain growth kinetics revealed a high grain growth exponent (n) ∼7, which confirmed a Zener-drag mediated process due to the ε nano-precipitates. The Hall-Petch analysis of the hardness data showed relatively high friction stress originating from the dissolution of Hf, Nb, and Ta in the FCC matrix. A high Hall-Petch coefficient indicated increased shear stress for plastic flow across the boundaries, resulting from the elongated Laves phase at the boundaries. The highly deformable Laves phase, ultrafine grain size, and ε nano-precipitates resulted in high yield strength (∼975 MPa) and superior ductility (∼16 %) in the (HfNbTa)_0.2 CCA, even surpassing the (Nb)_0.2 CCA. It was envisaged that strong yet deformable Laves phases could pave the pathway for developing Laves phase-based CCAs for advanced structural applications.

The early oxidation behaviors of complex Al–Cr compositional gradient coatings on a novel Co–Al–W substrate prepared by multi-arc ion plating technology (MIPT) at 1000 °C for 20–60 min were rapidly characterized. The as-deposited coatings with compositions ranging from (55%–90%Al, 45%–10%Cr) exhibited the laminated structure α-Al + Al₈₀Cr₂₀+Al₈Cr₅+α-Cr. After annealing at 640 °C for 40 h, a two-layered coating composed of (Co(Al, Cr) + Al₈Co₁₈Cr₄) and IRL formed, and the thickness of the coating increased from the 14–18 μm of the as-deposited state to 25–35 μm. During oxidation at 1000 °C for 20–60 min, a three-layer structure consisting of an outer α-Al₂O₃+α-Cr₂O₃+CoCr₂O₄ layer, a central unoxidized Al–Cr layer, and an inner μ-Co₇(W_0.55Cr_0.45) ₆+B₂–CoAl layer formed on the substrate. The Al–Cr coatings with higher Cr content had a looser oxide layer due to the CoCr₂O₄ phase, which might degrade the intended protective effect of the Al–Cr coatings. Thus, the Al–Cr coatings with higher Al content were suitable for preventing oxidation behavior. This work proposes a high-throughput screening method for rapid characterization of the early oxidation mechanism of the complex Al–Cr compositional gradient coatings.