Body-centered Cubic Structure Research Articles

Work-hardening ability enhancement of lightweight high entropy alloys via adding yttrium

Lightweight high-entropy alloys (LHEAs) with body-centered-cubic (BCC) structure have attracted wide attention due to their considerable strength-ductility synergy. However, the lack of work hardening ability is a key weakness, limiting the engineering application. In this study, appropriate contents of rare-earth element yttrium (Y) were added to the as-cast Ti-Zr-V-Nb-Al LHEAs with single BCC structure, and the microstructure and work hardening behavior of these LHEAs were investigated. Benefiting from the addition of Y, these LHEAs generated slight of Y-rich and Y-O-rich phases both in the grains and on the grain boundaries. During plastic deformation, these precipitates can effectively prevent dislocation slip and promote the dislocation intersections and reactions, which can improve the work-hardening ability. Moreover, adding Y can promote the large constitutional supercooling of the LHEAs and refine the grain size of the LHEAs, which also improve the work-hardening ability. Finally, the work hardening of as-cast Ti-Zr-V-Nb-Al LHEAs were successfully turned from negative to positive with 0.2 at% Y addition, with only few ductility loss. Our work provides an effective means of optimizing the mechanical properties, especially the work hardening ability, of as-cast BCC LHEAs.

Vibration characteristics of additive manufactured IWP-type TPMS lattice structures

Several research has been done on the conventional strut-based lattice structures, which have the problem of stress concentration in the application. In recent years, a new lattice structure, the triply periodic minimal surface (TPMS) lattice structure is increasingly gaining attention, but its vibrational properties have been less studied. In this study, the IWP-type TPMS lattice structures and ordinary body-centered cubic (BCC) counterparts with similar topology were prepared by selective laser melting (SLM) additive manufacturing (AM) technique. The compression behavior of the structures and the energy absorption capacity were determined by uniaxial compression tests. The frequency response and the damping ratio of the structure were calculated by dynamic vibration transfer rate tests. The results show that the stiffness and inherent frequency of the lattice structure are proportional to the volume fraction and inversely proportional to the cell size. Decreasing the volume fraction and increasing the cell size can be more beneficial to achieve low-frequency vibration isolation. Moreover, the IWP-type triply periodic minimal surface lattice structures have better mechanical properties than BCC structures and have good vibration isolation properties. Insights from this paper provide a reference for improving the load-carrying and vibration isolation performance of lightweight lattice structures.

Novel candidate of metal-based thermal barrier coatings: High-entropy alloy

To obtain compatible properties of low thermal conductivity and high thermal stability, Al0.6CoCrFeNiTi high-entropy alloy was designed as a novel candidate of metal-based thermal barrier coatings (MBTBCs). The corresponding high-entropy alloy coatings were fabricated by both high-velocity oxygen-fuel spraying (HVOF) and atmospheric plasma spraying (APS), and then the dependence of thermal insulation properties on microstructure was investigated. The both coatings exhibit a simple body-centered cubic (BCC) structure, but present obvious difference in microstructure and defect characters which relates to the evolution of in-flight particles. Benefit from the extremely low thermal conductivity, the APS-deposited coating can increase 13.24 °C of the surface temperature of piston crown and yield a temperature reduction of 19.00 °C along the thickness direction, which mean a positivity on enhancing the power efficiency of vehicle engines without sacrificing the strength of aluminum alloy components. In virtue of a decoupling method, the crucial effect of microstructure on thermal conductivity is disclosed, thus interpreting the excellent thermal insulation property of APS-deposited coating dominated by grain refinement and disordered BCC structure. The present results demonstrate a great potential of high-entropy alloy coatings as thermal barrier application and provide an inspiration for future works aiming to design these coatings to meet specific engineering needs.

Effect of Aluminum Addition on the Microstructure, Magnetic, and Mechanical Properties of FeCrCoNiMn High-Entropy Alloy

High-entropy FeCoCrNiMn (C1) and FeCoCrNiMn10Al10 (C2) alloys (HEAs) were mechanically alloyed for 24 h and heated to 900 °C (C1_900 °C and C2_900 °C). The powders were also compacted into pellets (C1_pellet and C2_pellet) and sintered at 500 °C for 1 h. Crystal structure, microstructure, magnetic, and mechanical properties were investigated by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, and microindentation. During the milling process, a mixture of body-centered-cubic (BCC) and face-centered-cubic (FCC) phases with a crystallite size in the range of 9–13 nm was formed in the C1 HEA alloy. The dual FCC + BCC solid solutions remain for the C1_pellet and transform to a single FCC for the C1_900 °C powders. Al addition stabilizes the BCC structure in the FeCoCrNiMn10Al10 HEA alloy, as revealed by the structural refinement. The structure exhibits a mixture of BCC + FCC solid solutions for the C2 powders and BCC + FCC + CrCo sigma phase for the C2_pellet and C2_900 °C powders. The crystallite sizes are in the range of 6-93 nm for all the samples. The saturation magnetization (Ms), coercivity (Hc), and squareness ratio (Mr/Ms) are estimated to be 24.2 emu/g, 153.62 Oe, and 0.165, respectively, for C1 and 28.45 emu/g, 188.48 Oe, and 0.172 for C2. The C1_900 °C and C2_900 °C powders exhibit, respectively, paramagnetic and soft magnetic behaviors and an exchange bias at room temperature. The C1_pellet and C2_pellet HEAs show high hardness values of 584.85 Hv and 522.52 Hv, respectively.

Preparation, characterization, and phase evolution of nanocrystalline Cu/Ti doped MoNbTa-based multi-principal element alloys

As multi-principal element alloys (MPEAs) continue to draw attention from researchers, there is a growing demand for MPEAs with a combination of body-centered cubic (BCC) and face-centered cubic (FCC) phases because of their intriguing properties. In the present study, we prepared MPEAs with BCC and FCC phases using composition optimization, mechanical alloying (MA), and powder sintering. Two alloys Mo25Nb25Ta25Cu25 and Mo28Nb28Ta28Cu8Ti8 (in at.%) were prepared from elemental powders. The phase evolution and composition were investigated from the powder processing stage to the annealing stage, using X-ray diffractometry and electron microscopy. As the milling times increase, the crystallite sizes were significantly refined. For the as-sintered Mo25Nb25Ta25Cu25, two different BCC structures were observed along with an FCC phase enriched in Cu. In contrast, the sintered Mo28Nb28Ta28Cu8Ti8 also exhibited the same dual-phase BCC structures but contained Ti-rich microprecipitates. The sintered Mo28Nb28Ta28Cu8Ti8 had a better balance of mechanical strength (1302 MPa) and plasticity (20%) compared to Mo25Nb25Ta25Cu25 alloy. Gibbs free energy calculations showed that the dual-phase BCC + FCC structure arose because of the miscibility gap between Cu and the refractory elements.

Design and experimental investigation of the high-entropy alloys AlCrFeNiCu and AlCrFeNbMo

To improve the service safety of accident-tolerant fuels in nuclear power plants, the high-entropy alloys (HEAs) AlCrFeNiCu and AlCrFeNbMo were designed and prepared through mechanical alloying (MA) and spark plasma sintering (SPS) processes in this work. The phase structures of AlCrFeNiCu and AlCrFeNbMo were predicted and verified. The microstructure, phase structure, and properties of alloy powders and sintered alloy were investigated under various ball-milling conditions. Results show that the phase formation rule of HEA is an empirical criterion that still needs experimental verification. The HEA powder was refined and had good fluidity after MA. Body-centered cubic (BCC) AlCrFeNbMo powder can be prepared at high milling speeds and long milling times, while the structure of AlCrFeNiCu powder was a BCC plus face-centered cubic (FCC) duplex phase structure. The spark plasma-sintered alloy had fine grains (＜1 μm) and a multiphase structure. AlCrFeNiCu was mainly composed of FCC, B2, and a trace of σ phase, while AlCrFeNbMo was composed of BCC, FCC, and σ phase. The density, hardness, compressive strength, yield strength and strain of AlCrFeNiCu and AlCrFeNbMo alloys were 6.54 g cm−3, 447.57 HV, 1727 MPa, 1642 MPa and 15% and 6.32 g cm−3,1188.82 HV, 2183 MPa, 1943 MPa, and 19%, respectively, which are higher than reported for most HEAs that were prepared by SPS. The fracture mechanism is the typical brittle fracture. Because of solution strengthening and precipitation strengthening, AlCrFeNiCu and AlCrFeNbMo have excellent mechanical properties.

Mechanical and corrosion properties of biomedical (TiZr)90-xNbxTa5Mo5 medium entropy alloys

High- or medium-entropy alloys with single phase body centered cubic (BCC) structure have attracted significant scientific interests recently, due to their great potentials for biomedical applications. However, BCC high entropy alloys generally do not have good tensile ductility at room temperature. Herein, we utilize the valence electron concentration (VEC) theory to design three (TiZr)90-xNbxTa5Mo5 (x = 5,10,15) biomedical medium entropy alloys (BioMEAs). The BioMEAs showed a single phase BCC structure, a low elastic modulus of 79.2 ± 1.6–82.9 ± 1.2 GPa, a good tensile ductility of 24.4%, and a high specific yield strength of 141.2–137.4 10−3 MPa∙m3/kg. The good tensile ductility of the alloys was found attributed to the cross-slip of mixed dislocations and the formation of kink bands, avoiding the excessive entanglement of dislocations and relieving stress concentration. The increase of Nb content (5–15 at.% Nb) contributed little to the yield strength of the BioMEAs. In addition, the (TiZr)90-xNbxTa5Mo5 alloys showed excellent corrosive resistance in modified Fusayama saliva (MFS) solution, in which passive films composed of a variety of oxides spontaneously developed on the exposed surfaces. Our work has cast new light to develop lightweight and economical BioMEAs with excellent comprehensive properties.

Design and Development of High-Entropy Alloys with a Tailored Composition and Phase Structure Based on Thermodynamic Parameters and Film Thickness Using a Novel Combinatorial Target.

This study presents a novel synthesis route for high-entropy alloys (HEAs) and high-entropy metallic glass (HEMG) using radio frequency (RF) magnetron sputtering and controlling the HEA phase selection according to atomic size difference (δ) and film thickness. The preparation of HEAs using sputtering requires either multitargets or the preparation of a target containing at least five distinct elements. In developing HEA-preparation techniques, the emergence of a novel sputtering target system is promising to prepare a wide range of HEAs. A new HEA-preparation technique is developed to avoid multitargets and configure the target elements with the required components in a single target system. Because of a customizable target facility, initially, a TiZrNbMoTaCr target emerged with an amorphous phase owing to a high δ value of 7.6, which was followed by a solid solution (SS) by lowering the δ value to 5 (≤6.6). Thus, this system was tested for the first time to prepare TiZrNbMoTa HEA and TiZrNbMoTa HEMG via RF magnetron sputtering. Both films were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, field emission scanning electron microscopy cross-sectional thickness, and atomic force microscopy (AFM). Furthermore, HEMG showed higher hardness 10.3 (±0.17) GPa, modulus 186 (±7) GPa, elastic deformation (0.055) and plastic deformation (0.032 GPa), smooth surface, lower corrosion current density (Icorr), and robust cell viability compared to CP-Ti and HEA. XRD analysis of the film showed SS with a body-centered cubic (BCC) structure with (110) as the preferred orientation. The valence electron concentration [VEC = 4.8 (<6.87)] also confirmed the BCC structure. Furthermore, the morphology of the thin film was analyzed through AFM, revealing a smooth surface for HEMG. Inclusively, the concept of configurational entropy (ΔSmix) is applied and the crystalline phase is achieved at room temperature, optimizing the processing by avoiding further furnace usage.

Mechanically alloyed and spark plasma sintered WNbMoVTa refractory high entropy alloys: Effects of Cr and Al on the microstructural and mechanical properties

In this study, WNbMoVTa refractory high entropy alloys (RHEAs) with a body-centered cubic structure (BCC) were produced in the presence of Cr and Al additions using mechanical alloying (MA) and spark plasma sintering (SPS) methods. Firstly, MA was conducted on the WNbMoVTa powders at different durations (2, 4, 6, and 8 h), and a single BCC phase was observed after MA for 2 h. The average crystallite size, lattice strain, and particle size for the 6 h MA’ed powders were measured as ∼8.10 nm, ∼2.50%, and ∼400 nm, respectively. Based on the analyses of the WNbMoVTa powders, 6 h was chosen as the optimum MA time. Secondly, different amounts of Cr and Al elements were added into the WNbMoVTa powders, and they were converted into WNbMoVTaCrxAly (x, y = 0, 0.5, 1.0 wt%) powders. Lastly, they were MA’ed for 6 h and SPS’ed at 1500 ºC under 30 MPa for 10 min. Composition, microstructure, density, microhardness, wear resistance, and thermal behavior properties were examined for all the sintered samples. MA’ed and SPS’ed WNbMoVTa samples showed the lowest microhardness (10.82 ± 0.12 GPa) and the highest wear volume loss (1.25 ×10−4 mm3) values. After additions of Cr and Al elements into the WNbMoVTa, microhardness increased to a maximum value of 13.06 ± 0.18 GPa, and wear volume loss decreased to a minimum value of 0.16 × 10−4 mm3. Also, the weight gain of the WNbMoVTa sample in the air decreased by adding Al and Cr elements. Thus, the mechanical and thermal properties of the WNbVMoTa sample were enhanced with the incorporating of Al and Cr elements.

Microstructure and First Hydrogenation Properties of Ti16V60Cr24−xFex + 4 wt.% Zr Alloy for x = 0, 4, 8, 12, 16, 20, 24

In body-centered cubic (BCC) alloys of transition elements, elemental addition or substitution in the vanadium-based alloys can be beneficial for improving the hydrogen storage properties and for reducing the production cost. In this context, the current study focused on the effect of the substitution of Cr by Fe in Ti16V60Cr24−xFex + 4 wt.% Zr alloys where x = 0, 4, 8, 12, 16, 20, 24. The microstructure of each alloy was composed of a matrix having a chemical composition close to the nominal one and a Zr-rich region. From X-ray diffraction patterns, it was found that the matrix has a BCC structure, and the Zr-rich regions present the C14 Laves phase structure. The lattice parameter of BCC phases decreased linearly with x, in accordance with Vegard’s law. The measurement of the first hydrogenation at 298 K under 3 MPa of hydrogen revealed a decrease in the maximum hydrogen capacity: 3.8 wt.% for x = 0, 3.1 wt.% for x = 4 and around 2 wt.% for x = 8 to 24. The XRD patterns after hydrogenation showed a BCT phase for all alloys, with a C14 phase for x = 4, 8, 12 and with C14 and C15 for x = 16, 20 and 24.

Elastic modelling of lattice distortions in concentrated random alloys

Lattice distortions, i.e. small atomic displacements away from the average lattice, are linked to a number of functional and mechanical properties of concentrated metallic alloys, particularly their yield strength. Here we develop an elastic model of lattice distortions where every atom is modeled as an Eshelby inclusion in a homogeneous elastic matrix. Local environment effects are included by considering fluctuating anisotropic eigenstrain tensors associated to the inclusions. The model is tested on several concentrated alloys, face-centered cubic (FCC) AlMg and FeNiCr alloys, as well as a fictitious body-centered cubic (BCC) binary alloy to study systematically and independently the effects of a size and an elastic modulus mismatch between the constituents. The elastic model predicts lattice distortions well when the size and elastic modulus mismatches are typically less than 5% and 25%, respectively. Interestingly, we find that when the size mismatch is small, as in FeNiCr alloys, the lattice distortion is dominated by the fluctuations of the dilatational eigenstrains rather than their average value as often assumed in elastic models of concentrated alloys. Moreover, models usually assume homogeneous elastic constants, while the limit obtained here of 25% is often exceeded in concentrated alloys, particularly with a BCC structure.

Finite element analysis of lattice designed lumbar interbody cage based on the additive manufacturing.

Additive manufacturing (AM) methods, which facilitate the production of complex structures with different geometries, have been used in producing interbody cages in recent years. In this study, the effects of Ti6Al4V alloy interbody lattice designed fusion cages between the third and fourth lumbar vertebrae where degenerative disc diseases occur were investigated using the finite element method. Face centered cubic (FCC), body centered cubic (BCC), and diamond structures were selected as the lattice structure suitable for the interbody cage. A kidney shaped interbody lumbar cage was designed. The designated lattice structures were selected by adjusting the cell sizes suitable for the designed geometry, and the mesh configuration was made by the lumbar lattice structure. 400 N Axial force and 7.5 N.m moments were applied to the spine according to lateral bending, flexion, and torsion. 400 N axial force and 7.5 N.m flexion moment is shown high strain and total deformation then lateral bending and torsion on BCC FCC and diamond lattice structured interbody cages. In addition, the effects of lattice structures under high compression forces were investigated by applying 1000 N force to the lattice structures. When von Mises stresses were examined, lower von Mises stress and strains were observed in the BCC structure. However, a lower total deformation was observed in the FCC. Due to the design of the BCC and the diamond structure, it is assumed that bone implant adhesion will increase. In the finite element analysis (FEA), the best results were shown in BCC structures.

Enhancement of damping capacity by deformation-induced martensitic transformation in Mg–Sc alloy

The effects of different crystallographic orientations of the grains on damping capacity (tanδ) were investigated using nano-dynamic mechanical analysis in pure magnesium, hexagonal close packed structure (HCP) Mg–20Sc (at.%), and body centred cubic structure (BCC) Mg–20Sc (at.%) alloy. In comparison to HCP Mg–Sc, the grain orientation has a significant impact on the tanδ of pure Mg and BCC Mg–Sc. Furthermore, the tanδ value of pure Mg at any given frequency were higher than those of HCP and BCC Mg–Sc samples due to the absence of the solute atom Sc.

Investigation of the heat transfer enhancement and deterioration induced by vortex generators in low Prandtl number sodium-potassium alloy liquid

Liquid metals, being characterized by low molecular viscosity and high molecular thermal conductivity, appear to be a stupendous choice for heat transfer fluids in deep-space nuclear reactors. Nevertheless, because of space nuclear reactor weight and volume constraints, the heat transfer capability of the heat exchanger must be substantially improved for a deeper space exploration mission. In this study, the influence of the vortex generator applied to the liquid metal was investigated to further promote the heat transfer capability of the liquid metal. And the thermo-fluid behaviors of the sodium-potassium alloy (NaK-78) are compared among the channel with the Body-Centered Cubic (BCC) lattice array, the rectangular ring rib array, and the Kagome lattice array under identical porosity. The numerical results indicate that the heat transfer deterioration phenomena occurred in the case of rectangular ring rib channel, which is a relatively rare occurrence in conventional fluids with the local Nu number even being lower than that of the smooth channel at the same location. Therefore, the rectangular ring rib should be carefully considered and evaluated when it is applied to heat transfer enhancement in NaK alloy fluid. The Kagome structure and the BCC structure could effectively promote the heat transfer performance of the NaK alloy fluid by means of the induced composite vortex system. In comparison to the smooth channel, the average Nu of the cases with the Kagome array and the BCC array yield 17.26–37.32% and 51.98–78.85% higher, respectively.

Design of a Ti–V–Nb–Cr alloy with room temperature hydrogen absorption/desorption reversibility

Computational thermodynamic tools are employed to design Ti–V–Nb–Cr alloys for hydrogen storage. Calculation of phase diagrams (CALPHAD) is employed to find compositions prone to form body centered cubic (BCC) alloys. A thermodynamic model to calculate pressure-composition-temperature (PCT) diagrams is used to select compositions with plateau pressure above 1 bar at room temperature. Three alloys are synthesized via arc melting and present predominantly BCC structures. The alloys show capacity to absorb hydrogen with fast kinetic without any activation treatment. PCT diagrams demonstrate reasonable values of plateau pressures and thermodynamic properties compared to calculated ones. Cycling experiments are measured to evaluate room-temperature reversibility in the Ti11V30Nb28Cr31 alloy. A continuous reduction in capacity is observed due to stabilization of the face centered cubic (FCC) hydride. The resistance to air exposure of the Ti11V30Nb28Cr31 alloy is investigated. The alloy demonstrated to be easily reactivated after air exposure by a heat treatment under dynamic vacuum.

Unveiling deformation twin nucleation and growth mechanisms in BCC transition metals and alloys

Twinning provides critical stress-relieving and flaw tolerance in body-centred cubic (BCC) transition metals (TMs) when dislocation plasticity is suppressed. Twin nucleation and growth mechanisms have been studied for over half a century without a consensus. Here, we use a reduced-constraint slip method to unveil the path to twin nucleation, growth and associated energy barriers in the entire BCC TM family. Twinning is surprisingly but essentially controlled by a normalized energy difference η between the hexagonal close-packed (HCP) and BCC structures in elemental TMs, and can be effectively tuned and quantitatively predicted by first-principles calculations in TM alloys. Fracture mechanics theory with η-based barriers enables predictions of critical solute concentrations to activate twinning and reverse ductile-to-brittle transitions in BCC TMs, as demonstrated in WRe alloys. The computational approach provides a unified and quantitative method to predict twinning and a practical tool for rapid screening of alloy compositions ensuring ductile behaviour.

Special hot working plastic deformation behavior and microstructure evolution mechanism of single-phase BCC structure AlFeCoNiMo0.2 high-entropy alloy

The single-phase body-centered cubic (BCC) structured high-entropy alloys are considered to be typically difficult-to-deform processing alloy because they can still crack during hot deformation at high temperatures and low strain rates. However, we found that the hot working formability of this type of alloy is very sensitive to temperature, and there is a unique microscopic transformation. In this paper, the as-cast single-phase BCC-structured AlFeCoNiMo0.2 high-entropy alloy was investigated with the single-pass hot-compression simulation experiment (deformation of 0.6), at temperatures and strain-rate ranges of 900 – 1150 ℃ and 0.001 – 0.1 s−1, respectively. The hot-deformation behavior and microstructure-evolution mechanisms were studied. The Arrhenius constitutive relation model was revised and established. The processing maps of Prasad, Gegel, Malas, and Murty with different instability criteria were constructed. The optimal thermal-processing parameters (temperatures of 1070 – 1150 ℃ and strain rates of 0.001 – 0.1 s−1) were provided. It was great to find that the alloy has a narrow temperature window effect of hot working with the Ruano-Wadsworth-Sherby (R-W-S) deformation-mechanism map established by incorporating the dislocation quantity. The deformation mechanisms of the alloy at 900 °C, 1000 °C, 1050 °C, and 1100 °C were predicted. The single-phase (BCC) structure of the alloy has strong stability during hot deformation. In a narrow range of hot-working temperatures, the microstructure has a necklace-like structure, and its substructure has a strong textured effect, impeding grain-boundary slip. In the optimized processing interval, discontinuous dynamic recrystallization (DDRX) occurs, and the necklace-like structure disappears. The recrystallization mechanism is related to grain-boundary sliding, caused by dislocation sliding.

First-principles studies of behavior of hydrogen and mechanical properties of TiCrTaV high-entropy alloys

This study investigates the dissolution and diffusion of H atom in TiCrTaV of two body-centered cubic (BCC) high-entropy alloys and their effects on the mechanical properties and electronic structure of the alloys by first-principles calculations. Results show that the solution energy of H atom and local lattice distortion vary depending on the local environment. Meanwhile, the site occupancy of H atoms in tetrahedral interstitials are slightly advantageous in the two structures. Diffusion of H also presents a sluggish effect. The dramatic increases and decreases of diffusion barrier disrupted the periodicity and symmetry of H diffusion in the two BCC structures, thereby slowing down the H accumulation. After hydrogenation, TiCrTaV high-entropy alloys (HEAs) still maintain resistance to deformation, indicating that they are the potential candidate structural materials for fusion reactors. Our investigation indicates that this low-activation HEA may exhibit promising irradiation resistance due to its special H behavior.

Microstructure evolution and performance enhancement of NbTaTiV-(Cr, Zr, W) single-phase refractory high-entropy alloy coatings: Role of additional elements

Refractory high entropy alloys (RHEAs) with single-phase structure hold far great potential in the field of surface protection application under extreme environment such as high temperature, abrasion and corrosion. In this work, the effects of Cr, Zr and W on the microstructure evolution and properties of a single-phase body-centered-cubic (BCC) NbTaTiV RHEA coating have been investigated. Experimentally, in addition to a small amount of Laves phase introduced by Cr element, NbTaTiV-(Cr, Zr, W) RHEA coatings basically maintain the single BCC structure. The addition of different elements affects segregation degrees in dendrite microstructure, and Zr shows nanoscale chemical heterogeneity. Notably, grain refinement, elevated geometrically necessary dislocation density and high-density low angle grain boundaries lead to a dramatically increase of micro-hardness due to elements addition. The wear rate of NbTaTiVCr and NbTaTiVW RHEA coatings reduce by 74.98 % and 70.79 % compared with NbTaTiV coating. The wide passive passivation zones close to 1000 mV obtained by potentiodynamic polarization exhibit excellent corrosion resistance. In addition, the formation mechanism of oxide layers is studied by thermodynamic parameters and oxidation behavior of simple oxides. The current work provides theoretical support for the application of strengthening elements in a single-phase BCC RHEA coating.

Additively Manufactured Half-Gutman Lens Antenna for Mobile Satellite Communications

In this letter, we present an additively manufactured half-Gutman lens antenna operating at 30 GHz. The hemispherical lens allows for a compact beamformer while maintaining the wide scanning capabilities of Gutman lenses. This solution further enables to better integrate the feed system when compared to a more conventional half-Luneburg lens antenna design as the focal arc is moved inside the lens. The graded-index of the lens is implemented with a periodic structure arranged in a body-centred cubic (BCC) lattice. We demonstrate that the BCC structure provides attractive properties for the design of inhomogeneous dielectric lenses. Importantly, the BCC structure can be used to alleviate the manufacturing constrains compared to conventional periodic structures. The lens is fed by a dielectric-loaded square waveguide. The proposed antenna produces a directive beam with a simulated and measured peak gain of 26.2 and 25.3 dBi. The antenna can steer its beam in a 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> range in elevation with measured scan loss and sidelobe levels below 1 dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB, which agree with the simulated values. The measured cross polarization discrimination is better than 20 dB. The proposed antenna is intended for the ground segment of the emerging low-Earth-orbit satellite communication applications.