Search Results (47)

Dual-beam circularly polarized antenna arrays are widely demanded in high-capacity wireless and satellite communication systems. However, conventional designs typically suffer from complex feeding networks, large profile, and high insertion loss, which limit their integration level and efficiency. To address these issues, this paper proposes a low-loss, highly integrated dual-beam circularly polarized antenna array based on a substrate-integrated waveguide equivalent ENZ feeding network. A new physical phenomenon is revealed that the tangential electric field in the slots exhibits an equal-amplitude and anti-phase distribution due to the combined effect of the uniform field distribution in the ENZ medium and the boundary conditions of the slotted perfect electric conductor. Using this inherent mechanism, the antenna achieves symmetric dual-beam radiation at approximately ±27° in the E-plane. A polarization conversion meta surface layer is loaded to convert linear polarization into circular polarization. A prototype is fabricated and measured. At 8.3 GHz, the measured peak gain is 9.1 dBi, the minimum axial ratio is better than 1.5 dB, and the radiation efficiency is higher than 85%. The proposed array features simple structure, low loss, and high integration. Compared with conventional feeding structures, it eliminates the need for additional phase shifters or power dividers, effectively reducing insertion loss and structural complexity. It exhibits good application potential in compact base stations and satellite communication terminals. Full article

Nickel ferrite (NiFe₂O₄) is one of the most studied inverse-spinel ferrites because it combines moderate saturation magnetization, comparatively high electrical resistivity, chemical stability, and broad synthesis flexibility. Yet the literature shows that the measured structure and magnetism of NiFe₂O₄ are not intrinsic constants; they evolve strongly with dimensionality, size, thickness, strain state, cation distribution, surface spin disorder, and synthesis pathway. This review develops a unified theoretical and literature-based interpretation of how dimensionality reshapes the structural and magnetic behavior of NiFe₂O₄ across bulk ceramics, nanoparticles, one-dimensional nanostructures, polycrystalline thin films, and ultrathin epitaxial films. The review is anchored in the two uploaded nickel ferrite attachments and expanded using internet-sourced journal literature on spinel inversion, surface effects, mechanochemical synthesis, sputtered and pulsed laser deposited thin films, and epitaxial ultrathin-film anomalies. The central novelty of this article is the formulation of a dimensionality-dependent framework in which the observed magnetic response is governed by a competition among three coupled factors: (i) the cation-distribution function, which controls the A–B superexchange balance and therefore the net ferrimagnetic moment; (ii) the microstructural coherence function, which measures how crystallinity, strain, defects, and anti-phase boundaries preserve or degrade exchange continuity; and (iii) the surface/interface spin-order parameter, which quantifies the loss or reconfiguration of magnetic order at free surfaces and buried interfaces. Within this framework, bulk NiFe₂O₄ behaves as a near-equilibrium inverse spinel with relatively stable magnetization, whereas nanoscale NiFe₂O₄ experiences strong spin canting and finite-size suppression due to the growing fraction of disordered surface spins. Thin films introduce a distinct regime in which strain, texture, anti-phase boundaries, substrate mismatch, and growth kinetics determine both anisotropy and magnetization. In ultrathin epitaxial films, off-equilibrium cation redistribution and interface-controlled electronic reconstruction may even generate magnetization values far above bulk expectations. The review also compares major synthesis routes—solid-state reaction, sol–gel, co-precipitation, hydrothermal growth, reactive milling, combustion, pulsed laser deposition, and radio-frequency sputtering—and explains why each route biases the final dimensionality-dependent properties differently. A set of word-style equations is provided to formalize spinel inversion, finite-size suppression, anisotropy scaling, coercivity trends, and superparamagnetic crossover. Beyond summarizing the field, the review proposes a regime map linking dimensionality to characteristic structural defects and magnetic signatures, and it identifies unresolved questions concerning the true origin of enhanced magnetization in ultrathin NiFe₂O₄, the interplay between anti-phase boundaries and strain, and the distinction between intrinsic inversion changes and extrinsic substrate artifacts. The resulting article offers a submission-ready, originality-focused review that positions dimensionality as the master variable governing structure–magnetism correlations in nickel ferrite. Full article

The crystal structure, texture, martensitic transformation, and magnetic properties of magnetic shape-memory Heusler alloys of Ni_51−xMn_33.4In_15.6V_x (x = 0; 0.1; 0.3; 0.5; 1) were investigated. Experimental studies of the magnetic properties and meta-magnetostructural transition (martensitic transition—MT) confirm the main sensitivity of the martensitic transition temperature to vanadium doping and to an applied magnetic field. This makes this family of shape-memory alloys promising for use in numerous applications, such as magnetocaloric cooling and MEMS technology. Diffuse electron scattering was analyzed, and the structures of the austenite and martensite were determined, including the use of TEM in situ experiments during heating and cooling for an alloy with a 0.3 at.% concentration of V. In the austenitic state, the alloys are characterized by a high-temperature-ordered phase of the L2₁ type. The images show nanodomain structures in the form of tweed contrast and contrast from antiphase domains and antiphase boundaries. The alloy microstructure in the temperature range from the martensitic finish to 113 K consists of a six-layer modulated martensite, with 10 M and 14 M modulation observed in local zones. The morphology of the double structure of the modulated martensite structure inherits the morphology of the nanodomain structure in the parent phase. This suggests that it is possible to control the structure of the high-temperature austenite phase and the temperature of the martensitic transition by alloying and/or rapidly quenching from the high-temperature phase. In addition, attention is paid to maintaining fine interface structures. High-resolution transmission electron microscopy showed good coherence along the austenite–martensite boundary. Full article

Aero-engine turbine vanes made from directionally solidified nickel-based superalloys often fail with crack formation from the external wall of cooling channels. Therefore, this study simulates the compressive load on the external wall of the vane and conducts a sequence of creep–fatigue evaluations at 980 °C to investigate the creep–fatigue damage mechanisms of a directionally solidified superalloy and to assess its life. It is found that at low strain ranges, creep damage is dominant, with creep cavities forming inside the specimen and fatigue sources mostly distributed in the specimen interior. As the strain range increases, the damage mechanism transitions from creep-dominated to creep–fatigue coupled damage, with cracks nucleating preferentially on the surface and exhibiting a characteristic of multiple fatigue sources. In the longitudinal (L) specimen, dislocations in multiple orientations of the {111}<110> slip system are activated simultaneously, interacting within the γ channels to form dislocation networks, and dislocations shear through the γ′ phase via antiphase boundary (APB) pairs. In the transverse (T) specimen, stacking intrinsic stacking faults (SISFs) accumulate within the limited {111}<112> slip systems, subsequently forming a dislocation slip band. The modified creep–fatigue life prediction model, incorporating strain energy dissipation and stress relaxation mechanisms, demonstrates an accurate fatigue life prediction under creep–fatigue coupling, with a prediction accuracy within an error band of 1.86 times. Full article

Directionally solidified (DS) superalloys have become a primary material choice for turbine blade applications. Due to the complex shape of the blades, certain regions inevitably experience stress axes oriented orthogonally to the crystal growth direction. Therefore, this study explores the creep characteristics of a DS superalloy in different orientations (transverse (T) versus longitudinal (L) with respect to grain growth direction) under intermediate and high temperatures (980 °C and 1070 °C), while simultaneously analyzing their respective deformation mechanisms and microstructural transformation behaviors. Experimental findings reveal pronounced orientation-dependent variations in creep performance, deformation modes, and microstructural development. Notably, the T specimen exhibits higher creep resistance at 980 °C, which can provide a basis for the design of some components that require high creep resistance and maintain small deformation. At 980 °C, L specimens primarily undergo γ′ phase shearing via antiphase boundaries (APBs) pairs, whereas T specimen exhibits APB pairs and superlattice intrinsic stacking faults (SISFs) shearing mechanisms. At 1070 °C, the L specimen exhibits dislocation shearing of γ′ alongside dislocation bypassing of tertiary γ′, while the T specimen demonstrates dislocation climbing within the γ channels. Additionally, the L specimen exhibits significant N-type rafting, while the T specimen shows significant Ostwald ripening characteristics, with an Ostwald ripening rate constant of 1.04 × 10⁻²⁰ m³/h. Full article

The creep properties of directionally solidified superalloys are largely influenced by the degradation rate of the γ/γ’ microstructure and the dislocation motion, which exhibit distinct mechanisms under varying temperature and stress conditions. In this study, the creep deformation mechanisms and microstructural evolution of a directionally solidified nickel-based superalloy in the longitudinal (L) and transverse (T) orientations at 850 °C are comprehensively investigated. Creep testing and characterization of the dislocation structure revealed superior creep properties in the L direction compared to the T direction. The creep mechanism in the L direction involves the activation of multiple {111}<110> slip systems, shearing the γ’ precipitates through antiphase boundaries (APBs). Conversely, the creep mechanism in the T direction involves the activation of {111}<112> slip systems, shearing the γ’ precipitates through a superlattice intrinsic stacking fault (SISF) and forming slip bands inclined to the stress axis. Aluminum was identified as the controlling element for the γ’ rafting. The longitudinal specimens exhibited P-type rafting due to the activation of multiple slip systems and sufficient plastic strain flow from the dislocation motion. In contrast, the transverse specimens show little rafting due to limited slip system activation. These findings can serve as a reference for better understanding the anisotropy of directionally solidified superalloys and provide a basis for their broader application. Full article

Materials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromising their safety during cryogenic temperature service. This study investigates the quasi-static mechanical properties of a CoCr₀.₄NiSi₀.₃ medium-entropy alloy (MEA) at room temperature, −75 °C, and −150 °C. The deformation behavior and mechanisms responsible for strengthening and toughening at reduced cryogenic temperatures are analyzed, revealing that decreasing cryogenic temperature enhances the strength of the as-cast MEA. Specifically, both the yield strength (YS) and ultimate tensile strength (UTS) of the MEA increase significantly with decreasing temperature during cryogenic tensile testing. Under tensile testing at −150 °C, the YS reaches 617.5 MPa, the UTS is 1055.0 MPa, and the elongation to fracture remains approximately 21.0% at both −150 °C and −75 °C. After cryogenic temperature tensile deformation, the matrix exhibits a dispersed distribution of nanoscaled tetragonal and orthorhombic phases, a coherent hexagonal close-packed phase, L1₂ phase and layered long-period stacking ordered (LPSO) structures, which are rarely observed in the cryogenic deformation of metals and alloys. The metastable phase evolution path of this MEA at cryogenic temperatures is closely associated with the decomposition of perfect dislocations into a/6<112> Shockley partial dislocations and their subsequent evolution at reduced cryogenic temperatures. At −75 °C, the a/6<112> Shockley partial dislocation interacts with the L1₂ phase to form antiphase boundaries (APBs) approximately 3 nm thick. At −150 °C, two phase transition paths from stacking faults (SFs) to nanotwins and LPSO occur, leading to the formation of layered LPSO structures and deformation-induced nanotwins. The dispersion of these coherent nanophases and nanotwins induced by the reduced stacking fault energy under cryogenic temperatures is the key factor contributing to the excellent balance of strength and plasticity in the as-cast MEA, providing an important basis for research on the cryogenic mechanical properties of CoCrNi-based MEAs. Full article

The anomalous flow behavior of the γ′-Ni₃Al phase at high temperature is closely related to a cross-slip of $1/2⟨110⟩\left\{111\right\}$ super-partial dislocations. The acceleration of cross-slips induced by the addition of rhenium (Re) is known as Re-effects. In this work, by means of a series of lattice transitions, a hybrid model including a preexisting anti-phase boundary $\mathrm{APB}\left(111\right)$ was constructed to assess the difficulty of cross-slips of $1/2⟨110⟩\left\{111\right\}$ super-partial dislocations from $\left\{111\right\}$ planes to $\left\{001\right\}$ planes in the γ′-Ni₃Al phases, and the impact of the addition of Re on these dislocation mediated creep resistances was reinvestigated by first-principles calculations. The results showed that the addition of Re at preferential Al sublattice sites was indeed beneficial for the cross-slip of the first leading $1/2⟨110⟩\left\{111\right\}$ super-partial dislocations, and the existence of $\mathrm{APB}\left(111\right)$ could promote cross-slip of second leading $1/2⟨110⟩\left\{111\right\}$ super-partial dislocations. A detailed calculation of stacking fault energies demonstrated that an obvious Suzuki segregation of Re existed at $\mathrm{APB}\left(111\right)$ and $\mathrm{APB}\left(001\right)$, and Re preferentially occupied Ni sublattice sites. It is found Re-segregations at $\mathrm{APB}\left(111\right)$ were disadvantageous for the cross-slip of new $1/2⟨110⟩\left\{111\right\}$ super-partial dislocations, but the formation of more Kear-Wilsdorf dislocation locks could benefit from Re-segregations at $\mathrm{APB}\left(001\right)$. Full article

Scapolite forms solid solutions between the end members marialite, Na₄[Al₃Si₉O₂₄]Cl = Me₀, and meionite, Ca₄[Al₆Si₆O₂₄]CO₃ = Me₁₀₀. Al-Si order and chemical composition models are proposed for the scapolite solid solutions. These models predict the chemical composition, Al-Si order, and average <T–O> distances between Me₀–Me₁₀₀. These models are based on the observed order of clusters and on two solid solutions that meet at Me₇₅ coupled with predicted chemical compositions and <T–O> distances. The [Na₄·Cl]³⁺ and [NaCa₃·CO₃]⁵⁺ clusters are ordered between Me₀–Me₇₅, whereas the clusters [NaCa₃·CO₃]⁵⁺ and [Ca₄·CO₃]⁶⁺ are disordered from Me₇₅–Me₁₀₀. To confirm the structural model, the crystal structure of 27 scapolite samples between Me₆–Me₉₃ has been obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. The structure was refined in space group P4₂/n for all the samples. The <T–O> distances indicate that the T1 (=Si), T2 (=Al), and T3 (=Si) sites are completely ordered at Me_37.5, where the 1:1 ratio of [Na₄·Cl]³⁺:[NaCa₃·CO₃]⁵⁺ clusters are ordered and gives rise to antiphase domain boundaries (APBs) based on Cl-CO₃ order instead of Al-Si order. The presence of APBs based on Cl-CO₃ order and cluster order indicate that neither space group P4₂/n nor I4/m are correct for the structure of scapolite, but the lower symmetry space group P4₂/n is a good approximation for modeling the average structure of scapolite. The complete Al-Si order at Me_37.5 changes in a regular and predictable manner toward the end members: Me₀, Me₇₅, and Me₁₀₀. The observed unit cell and several structural parameters show a discontinuity at Me₇₅, where the series is divided into two. There is no structural evidence to support any phase transition in the scapolite series. The T1 site contains only Si from Me₀–Me_37.5; from Me_37.5–Me₁₀₀, Al atoms enter the T1 site and the <T1–O> distance increases linearly to Me₁₀₀. Full article

Changing film thickness to manipulate microstructural properties has been considered as a potential method in practical application. Here, we report that atomic-scale structural properties are regulated by film thickness in an NiC_O2O₄(NCO)/CuFe₂O₄(CFO) bilayer heterostructure prepared on (001)-MgAl₂O₄ (MAO) substrate by means of aberration-corrected scanning transmission electron microscopy (STEM). The misfit dislocations at the NCO/CFO interface and antiphase boundaries (APBs) bound to dislocations within the films are both found in NCO (40 nm)/CFO (40 nm)/MAO heterostructures, contributing to the relaxation of mismatch lattice strain. In addition, the non-overlapping a/4[101]-APB is found and the structural transformation of this kind of APB is resolved at the atomic scale. In contrast, only the interfacial dislocations form at the interface without the formation of APBs within the films in NCO (10 nm)/CFO (40 nm)/MAO heterostructures. Our results provide evidence that the formation of microstructural defects can be regulated by changing film thickness to tune the magnetic properties of epitaxial bilayer spinel oxide films. Full article

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm³) have excellent compressive-specific yield strength (${\mathsf{\sigma }}_{\mathrm{YS}}$/$\mathsf{\rho }$) at 1023 K (~131 MPa·cm³/g) and 1123 K (~104.2 MPa·cm³/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](10$\stackrel{\_}{1}$) and [111](11$\stackrel{\_}{2}$) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K. Full article

The effect of the melt cooling rate on the atomic ordering of austenite and, as a consequence, on the martensitic transformation of a nonstoichiometric alloy of the Ni-Mn-In system has been studied. In situ TEM observations revealed differences in the mechanism of phase transformations of the alloy subjected to different cooling conditions. It is shown that during quenching a high density of antiphase boundaries (APB) is formed and the alloy is in the austenite–martensitic (10M and 14M) state up to a temperature of 120 K. In a slowly cooled alloy, a lower APB density is observed, and a two-stage transformation, L21/B2 → 10M → 14M, occurs in the range of 150–120 K. Full article

Precipitation behaviors of Ni-Cr-Co-based superalloys with different Ti/Al ratios aged at 750, 800, and 850 °C for up to 10,000 h were investigated using scanning and transmission electron microscopy. The Ti/Al ratio did not significantly affect the diameter of the γ′ phase. However, the volume fraction of the γ′ phase increased with increasing Ti/Al ratios. The η phase was not observed in alloys with a small Ti/Al ratio, whereas it was precipitated after aging at 850 °C for 1000 h in alloys with a Ti/Al ratio greater than 0.80. Higher aging temperatures and higher Ti/Al ratios led to faster η formation kinetics and accelerated the degradation of alloys. It is thought that the increase in hardness with an increase in the Ti/Al ratio is attributed to the effective inhibition of the γ′ phase on dislocation movement due to the increase in the volume fraction of the γ′ phase and an increase in the antiphase boundary (APB) energy. Full article

As the primary choice for aero-engine turbine blades, creep resistance is an important mechanical property for the developing third-generation single crystal Ni-based superalloys. The creep behavior of the superalloy in the [001] orientation was studied at 980 °C under a series of stress levels, accompanied with scanning electron microscope (SEM) and transmission electron microscope (TEM) observation to investigate the microstructure and deformation mechanism. The deformation mechanism of the alloy is found to be dislocation gliding, propagating and forming a dislocation network in the γ/γ′ interface. Dislocation networks could hinder the movement of dislocation and decrease the creep rate to a constant during the steady-creep stage. The formation of dislocation networks was analyzed due to the interaction of <110> {111} dislocations. Then dislocations cut into γ′ phases as individual <110> super-dislocations, anti-phase boundary dislocation pairs, and stacking faults. The <110> super-dislocation in the γ′ phase may cross-slip into the {001} plane from the {111} plane to form Kear–Wilsdorf locks, which could inhibit dislocations from gliding or cross-slipping and then enhance the creep resistance. Full article

Significant interest in the stoichiometric and off-stoichiometric Fe₂MnGa alloys is based on their complex phase transition behavior and potential application. In this study, temperature- and magnetic-field-induced phase transformations in the Fe_41.5Mn₂₈Ga_30.5 magnetic shape memory alloy were investigated by in situ synchrotron high-energy X-ray diffraction and in situ neutron diffraction techniques. It was found that incomplete phase transformation and phase coexistence behavior are always observed while applying and removing fields in Fe_41.5Mn₂₈Ga_30.5. Typically, even at 4 K and under 0 T, or increasing the magnetic field to 11 T at 250 K, it can be directly detected that the martensite and austenite are in competition, making the phase transition incomplete. TEM observations at 300 K and 150 K indicate that the anti-phase boundaries and B2 precipitates may lead to field-induced incomplete phase transformation behavior collectively. The present study may enrich the understanding of field-induced martensitic transformation in the Fe-Mn-Ga magnetic shape memory alloys. Full article