Wensheng Liu

Residual hydroxyl species and carbon inherited from sol-gel precursors affect the γ→α transformation of alumina, but their respective roles in transformation behavior and microstructure development remain unclear. In this study, the Al/acid ratio of aluminium carboxylate sols was varied to regulate the residual hydroxyl and carbon contents in alumina fibers. The resulting hydroxyl and carbon contents varied non-monotonically with precursor composition, with hydroxyl species remaining substantially more abundant than residual carbon after pre-sintering. An elevated hydroxyl content retarded α-Al2O3 formation: the high-hydroxyl fiber showed no detectable α-Al2O3 until approximately 1100 °C, whereas α-Al2O3 was already detected at 800 °C in the low-hydroxyl fiber. The radially organized α-Al2O3 domains developed only in carbon-containing fibers and were absent from the carbon-free sample under comparable thermal conditions. These findings indicate that residual hydroxyls hinder the local structural rearrangement required for the γ→α transformation, whereas carbon-related reactions above approximately 800 °C may facilitate dehydroxylation and local mass transport, thereby promoting spatially localized α-Al2O3 formation. Subsequent orientation-selective growth from these locally formed α nuclei provides a plausible origin for the radial organization. The results therefore reveal distinct but coupled roles of precursor-derived hydroxyls and carbon in controlling the onset and spatial evolution of the γ→α transformation in sol-gel alumina fibers.

Achieving a superior combination of ultra-high strength and satisfactory ductility remains an arduous challenge in aluminum alloy design. In this work, an Al-Zn-Mg-Cu alloy containing 0.1 wt.% Y is prepared by conventional casting and exhibits an ultimate tensile strength of 804 MPa together with a superior elongation of 8.0%. The results reveal that 0.1 wt.% Y addition refines the average as-cast grain size from 92 to 53 μm. Density-Functional-Theory calculations demonstrate the mutual substitution of Y and Zr on the minority sublattice is thermodynamically favorable, which promotes the transformation of Al3Zr to Al3(Zr,Y) dispersoids during homogenization process. The high diffusion coefficient of Y atom promotes the uniform and high-density precipitation of Al3(Zr,Y) dispersoids. These Al3(Zr,Y) dispersoids, characterized by a higher number density and smaller size, exert a stronger Zener pinning effect and reduce the recrystallization fraction of alloy from 18.9% to 7.6%. TEM and APT results show the trace addition of Y does not alter the precipitation kinetics or size distribution of η′ phase during aging process. But excessive Y will generate coarse insoluble secondary phases, which induce stress concentration and initiates cracking during deformation and thus reduce the alloy’s ductility.

Achieving a superior combination of ultra-high strength and satisfactory ductility remains an arduous challenge in aluminum alloy design. In this work, an Al-Zn-Mg-Cu alloy containing 0.1 wt.% Y is prepared by conventional casting and exhibits an ultimate tensile strength of 804 MPa together with a superior elongation of 8.0%. The results reveal that 0.1 wt.% Y addition refines the average as-cast grain size from 92 to 53 μm. Density-Functional-Theory calculations demonstrate the mutual substitution of Y and Zr on the minority sublattice is thermodynamically favorable, which promotes the transformation of Al3Zr to Al3(Zr,Y) dispersoids during homogenization process. The high diffusion coefficient of Y atom promotes the uniform and high-density precipitation of Al3(Zr,Y) dispersoids. These Al3(Zr,Y) dispersoids, characterized by a higher number density and smaller size, exert a stronger Zener pinning effect and reduce the recrystallization fraction of alloy from 18.9% to 7.6%. TEM and APT results show the trace addition of Y does not alter the precipitation kinetics or size distribution of η′ phase during aging process. But excessive Y will generate coarse insoluble secondary phases, which induce stress concentration and initiates cracking during deformation and thus reduce the alloy’s ductility.

Achieving a superior combination of ultra-high strength and satisfactory ductility remains an arduous challenge in aluminum alloy design. In this work, an Al-Zn-Mg-Cu alloy containing 0.1 wt.% Y is prepared via conventional casting, which achieves an ultimate tensile strength of 804 MPa and a superior elongation of 8.0%. The results reveal that 0.1 wt.% Y addition refines the average as-cast grain size from 92 to 53 μm. Density-Functional-Theory calculations demonstrate the mutual substitution of Y and Zr on the minority sublattice is thermodynamically favorable, which promotes the transformation of Al3Zr to Al3(Zr,Y) dispersoids during homogenization process. The high diffusion coefficient of Y atom promotes the uniform and high-density precipitation of Al3(Zr,Y) dispersoids. These Al3(Zr,Y) dispersoids, characterized by a higher number density and smaller size, exert a stronger Zener pinning effect and reduce the recrystallization fraction of alloy from 18.9% to 7.6%. TEM and APT results show the trace addition of Y does not alter the precipitation kinetics or size distribution of η′ phase during aging process. But excessive Y will generate coarse insoluble secondary phases, which induce stress concentration and initiates cracking during deformation and thus reduce the alloy’s ductility.

The mechanical response and failure behavior of structural materials, particularly dual‐phase alloys, over wide strain rate ranges are key determinants of their service performance. This study taken the typical BCC/FCC dual‐phase 90W–7Ni–3Fe (wt%) alloy as an example. Using universal testing machines (UTM), split Hopkinson tensile bars (SHTB), laser shock (LS) loading, molecular dynamics (MD) simulations, and advanced characterization techniques, it systematically investigated the influence of deformation mechanisms on mechanical response and failure behavior under strain rates spanning 10 ^–3 –10 ⁹ s ⁻¹ . At low/medium strain rates, deformation in both W particles and the γ phases was dominated by dislocation slip. At ultra‐high strain rates, W particles transitioned from dislocation slip to parallel {112} < 111 > nanotwins, while the γ phases shifted to parallel {111} < 112 > nanotwins, ultimately forming 70.52° rhombic intersecting nanotwins. The dual‐stage strength leap mechanism emerged, comprising dislocation density‐dominated continuous strengthening (10 ^–3 –10 ³ s ⁻¹ ) and twin‐dominated abrupt strengthening (≥ 10 ⁷ s ⁻¹ ). The fracture strength increased from 998.37 to 7466.51 MPa. The fracture mode underwent a transformation, with the formation of microcracks and the propagation of microcracks shifting from the W/γ interface to the interior of the W particles.

Traditional metal alloys require energy-intensive processes to manage atomic complexity for improved strength and toughness, with stringent control over impurities and processing conditions. High-/medium-entropy alloys (HEAs/MEAs) offer a sustainable alternative by introducing atomic complexity with fewer constraints, enabling unique phase transitions. Here, a Cu–Au–Ag MEA is fabricated using vacuum suspension melting followed by heat treatment. The alloy exhibits three distinct levels of heterogeneous structures: micron-scale phase separation, nano-ordered L1₂ phase, and chemical short-range order (CSRO). It demonstrates tensile and compressive strengths of 550 MPa and 1700 MPa for the micropillar sample, respectively, with 25% tensile elongation and over 50% compressive strain. The large-scale sample achieves a tensile strength and elongation of about 500 MPa and 40%, respectively. Compared to traditional gold, silver, and copper alloys, both the strength and plasticity are enhanced. The microstructural characteristics and corresponding mechanical properties are found to match the experimental structure through high-temperature ternary alloy phase diagrams and simulations. This work introduces a alloy design approach that leverages atomic affinity manipulation to regulate multilayer heterogeneous structures, which offers an efficient pathway for designing MEAs suitable for demanding high-performance electronic packaging applications.

The effects of (Zn + Mg) total content (9.6–11.7 wt.%) combined with multi-directional forging (MDF) on the microstructure and properties of high-strength Al–Zn–Mg–Cu alloys were systematically investigated. Our results demonstrate that the alloy obtains significant grain refinement, which is attributed to the dynamic recrystallization in the MDF process. Specifically, Al-8.6Zn-1.55Mg-1.9Cu-0.11Zr (Zn + Mg = 10.15 wt.%) obtains the maximum recrystallization ratio (51.8%) and the weakest texture strength, and also forms the mortise and tenon nested grain structure. Increasing the total (Zn + Mg) content can achieve significant performance enhancement, which is attributed to the refinement of the η′ phase; however, a higher total (Zn + Mg) content will lead to the continuous distribution of coarse η-MgZn₂ phases formed along the grain boundary, accompanied by the broadening of precipitate-free precipitation zones (PFZs). Compared with other alloys, Al-8.6Zn-1.55Mg-1.9Cu-0.11Zr (Zn + Mg = 10.15 wt.%) maintains high strength while ensuring desirable plasticity due to its mortise and tenon nested grain structure. In addition, its desirable grain boundary precipitation behavior makes it exhibit the best corrosion resistance. These findings indicate that maintaining the total (Zn + Mg) content around 10 wt.% achieves a balance between strength and corrosion resistance, offering a theoretical foundation for the design of high-strength and corrosion-resistant Al–Zn–Mg–Cu alloys.

Optimizing the design of low-tungsten-content alloys represents an effective approach to address the insufficient strength and toughness of conventional tungsten alloys. This study focuses on the design and fabrication of low-tungsten-content alloys, specifically investigating the effects of Nb addition on the low-temperature sintering microstructure and mechanical properties of 50W–Ni–Fe alloy. The results demonstrate that Nb significantly lowers the liquid phase formation temperature, shifting the densification mechanism from solid phase sintering to liquid phase sintering. Nb primarily dissolves in the γ-(Ni,Fe) matrix phase and forms nanoscale γ″-Ni₃Nb precipitates. These γ″-Ni₃Nb precipitates maintain coherent interfaces with the γ-(Ni,Fe) matrix phase, exhibiting excellent interfacial bonding, which markedly enhances the hardness and modulus of the matrix phase. Through the strengthening effects of solid solution strengthening and precipitation strengthening, the tensile strength of the alloy increases to 1259 MPa while maintaining a total elongation of 23.1%. The fracture mode of the 50W-Ni-Fe-Nb alloy transitions to a mixed mechanism involving cleavage fracture of W and ductile rupture of the matrix phase.

The existing Al-Ce heat-resistant alloys are not extensively utilized in high-temperature applications due to their poor room-temperature mechanical properties. In this study, the Al-10Ce-3Mg-5Zn alloy was enhanced using hot extrusion and heat treatment. The as-extruded alloy exhibited bimodal intermetallic compounds and grain structures. Additionally, high-density microcracks and twins were observed in the micron-sized intermetallic compounds. Compared with the as-cast state, the as-extruded alloy demonstrated a higher ultimate tensile strength (UTS) of 317 MPa and better elongation of 11.0%. Numerous nano-sized T phases precipitated in the α-Al matrix after the heat treatment, contributing to a further rise in UTS (365 MPa). The high strength of the alloy is primarily due to its strong strain hardening capacity, fine grain strengthening, and precipitation strengthening effect. The change in elongation mainly results from the expansion of pre-existing microcracks, twin deformation, and microstructural refinement. The heat-treated alloys exhibited superior strength retention ratios at elevated temperatures (64% at 200 °C) compared to conventional heat-resistant aluminum alloys. The results of this paper indicate that hot extrusion and heat treatment are effective for developing heat-resistant Al-Ce alloys with high room-temperature strength, offering a simple process suitable for industrial production.

This study systematically investigated the effects of the addition of the rare earth element yttrium (Y) on the microstructural evolution, mechanical properties, and corrosion behavior of as-extruded Al-5.6Zn-2.5Mg-1.6Cu-0.20Cr (wt.%) alloy through comprehensive characterization techniques, including X-ray diffraction (XRD), tensile testing, corrosion analysis, and electron microscopy. Microstructural characterization demonstrated that the incorporation of yttrium resulted in significant refinement of secondary phase particles within the as-extruded alloy matrix. Moreover, quantitative analysis revealed a substantial increase in low-angle grain boundary (LAGB) density, dislocation density, and the formation of subgrain structures. Notably, the volume fraction of η′ strengthening precipitates showed a marked increase, accompanied by a corresponding reduction in the width of precipitate-free zones (PFZs) along grain boundaries. Following the T74 aging treatment, the alloy with 0.1 wt.% yttrium addition exhibited a remarkable improvement in intergranular corrosion resistance, with the maximum corrosion depth reduced to 107.8 μm. However, it should be noted that the exfoliation corrosion resistance exhibited an inverse correlation with increasing yttrium content, suggesting a concentration-dependent behavior in corrosion performance.