Body-centered Cubic Structure Research Articles

Exceptional tensile ductility and strength of a BCC structure CLAM steel with lamellar grains at 77 kelvin

The low-temperature tensile brittleness of body-centered cubic (BCC) metals and alloys can seriously compromise their service applications. In this study, we prepared a BCC structured China low activation martensitic steel (CLAM) steel with lamellar grains by regulating the rolling and heat-treatment processes, successfully reversing the decreasing trend of ductility in the steel with decrease in temperature. Compared with current face-centered cubic (FCC) structural steels and high-entropy alloys, the lamellar grained CLAM steel exhibits an excellent synergy of strength and ductility at 77K, but with lower raw material costs. The superior low temperature ductility of the lamellar grained steel can be attributed to an increase in grain strength at low temperatures which promotes the propagation of layered tearing cracks; this in turn leads to a significant increase in the necking area of the steel, thereby compensating for the decrease in ductility. We conclude that our lamellar grain structures can be utilized to significantly enhance the low-temperature tensile ductility of BCC metals and alloys, thereby expanding their service range to cryogenic temperatures.

The effects of Nb on the microstructure and performance of laser-cladded Fe50-xMn30Co10Cr10Nbx high entropy alloy coatings

A laser cladding technique was employed to produce a Fe50-XMn30Co10Cr10NbX (X = 2.5, 5, 7.5, 10at%) high entropy alloy coating. This study delved into the influence of Nb concentration on the coating’s phase constitution, microstructural features, hardness, and wear resistance. The high entropy alloy coating exhibited a multifaceted structural composition, encompassing FCC (Face-Centered Cubic), HCP (Hexagonal Close-Packed), and BCC (Body-Centered Cubic) structures, along with the presence of Laves phase. Notably, the incorporation of Nb led to an augmentation in the Laves phase and modifications within the microstructure. The hardness of the cladding layer is higher than that of the substrate. With the increase of Nb content, the hardness of the cladding layer increases first and then decreases; the average hardness of the Fe42.5Mn30Co10Cr10Nb7.5 cladding layer is the highest, the maximum hardness is 429.8Hv, and the average hardness is 382.3Hv. The friction coefficient and weight loss of the cladding layer decreases first and then increases with the increase of Nb content. The friction coefficient and weight loss of the Fe42.5Mn30Co10Cr10Nb7.5 cladding layer are the smallest, which are 0.0132 g and 0.5974, showing the best wear resistance. The wear types of high entropy alloy cladding layer are both adhesive wear and abrasive wear. The addition of Nb into high entropy alloy will form the Laves phase, which can improve the mechanical properties of high entropy alloy.

Competitive relationship between the FCC + BCC dual phases in the wear mechanism of laser cladding FeCoCrNiAl0.5Ti0.5 HEAs coating

This work elaborated the microstructure and wear behavior of laser cladding (LC) FeCoCrNiAl0.5Ti0.5 high-entropy alloys (HEAs) coatings on AISI 1045 steel substrates. The microstructure of the HEAs coatings is mainly comprised of a body-centered-cubic (BCC) + face-centered-cubic (FCC) dual-phase structure. Besides, the coating exhibites high hardness. During the friction process, the FCC phase was more prone to deformation and peeling than BCC structure. As the alloying elements (such as Al, Ti, and Cr) tend to form oxide film at high temperatures during friction, the friction process of the LC FeCoCrNiAl0.5Ti0.5 coating was mainly controlled by oxidative wear and adhesive wear mechanisms. Friction test results showed that the coating owned excellent wear resistance and the wear rate of the HEAs coating was only 6.53 % of the wear rate of the steel substrate.

Design of metamaterial thermoelectric generators for efficient energy harvesting

Thermoelectric generators (TEGs) are widely recognized as clean energy solutions that can convert low-grade waste heat into electricity through a temperature gradient. Despite their significant potential, challenges such as low conversion efficiency and high costs have limited their practical applications. In this paper, we present an innovative metamaterial design concept for TEGs with significantly improved efficiency. A Finite Element Model is validated using Bi0.5Sb1.5Te3 bulk samples fabricated via the drop-cast method. This model can predict open-circuit voltage and output power as a function of an arbitrary metamaterial design using the commercial software ANSYS®. Four different metastructure designs, including 2D Triangular Honeycomb, Re-entrant, body-centered cubic (BCC), and triply periodic minimal surface (TPMS) structures, are systematically investigated. Through experiments and numerical analysis, the effects of annealing temperature, porosity, and unit cell numbers (UCNs) on the performance of TE legs are explored. It is found that 2D Triangular Honeycomb and BCC structures outperform other configurations due to their capacity to maintain a higher thermal gradient. Optimizing their porosity and UCNs can further enhance the output power. Compared to the traditional designs with bulk TE legs, implementing a 2D metastructure design with 30 % porosity and UCNs of 4 × 4 × 4 can lead to approximately a 100 % increase in power output.

Effect of Al content on microstructure and mechanical properties of the (FeCoNiV)100-xAlx high-entropy alloys

It is well known that face-centered cubic (FCC) high-entropy alloys (HEAs) typically have excellent ductility at room temperature but relatively low strength, which greatly limits their structural applications. To address the strength-ductility trade-off, researchers synthesized a series of (FeCoNiV)100-xAlx (x = 0–20 at. %) HEAs, investigated the effect of alloying Al on microstructure and tensile properties, then analyzed the strengthening mechanism. It was found that the crystalline structure changed from an initial single FCC structure to a duplex FCC plus body-centered cubic (BCC) structure and then to a single BCC structure with increasing Al concentration. After homogenization process, the FCC and BCC phases can be transformed to ordered L12 and B2 phases, respectively. These HEAs with duplex FCC/L12 plus BCC/B2 structure exhibit the potential for excellent mechanical properties, and their properties can be modulated by Al content and heat treatment. The properties can be tuned by both Al content and heat treatment, as the Al content can modulate the BCC phase content and the heat treatment can change the ordered structure. A careful analysis reveals that the solid solubility of Al element in this system was only 3.6 at. %, which has a limited effect on the strength. FCC/L12 bears the main plastic strain and the high tensile strength of the alloy is achieved thanks to the contribution of the BCC/B2 phase to the work-hardening rate of the alloy during the early stages of deformation and the unique work-hardening ability of the L12 phase.

Effects of Ti substitution by Zr, on the microstructure and hydrogen storage properties OF Ti2-xZrxCrV (x = 0.5, 1, 1.5, 2) alloys

The effect of the substitution of Ti by Zr on the crystal structure, microstructure, and first hydrogenation behavior of Ti2-xZrxCrV where X = 0.5, 1.0, 1.5, and 2.0 have been investigated. The samples were synthesized by arc-melting and characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The hydrogenation capacity was measured using a home-made Sieverts apparatus. Pure-Ti2CrV crystallizes in a body-centered cubic structure (BCC). Substitution of Ti by Zr leads to the appearance of a secondary phase, namely a C15 Laves phase for the Ti-containing samples, and C15 Laves phase plus a Zr-rich phase for the X = 2.0 sample. The substitution of Ti by Zr increased the lattice parameters in both phases for all samples. Increasing Zr content made the first hydrogenation faster but reduced the hydrogen capacity.

Experiment and numerical investigation on beetle elytra inspired lattice structure: Enhanced mechanical properties and customizable responses

The elytra of the ironclad beetles possess very strong and toughness performance, to protect the body from catastrophic physical damage, owing to its unique curved geometry and layered microstructure. In this paper, inspired by the elytra of ironclad beetles, a novel configuration of lattice structure (IBCC) was developed. The digital light processing (DLP) with hard-tough resin was used to fabricate the lattice structures. The compression experiment and simulation were performed to investigate the mechanical response and deformation mechanism. The response surface model (RSM) was adopted to build a forward relationship between structure parameters and mechanical properties. A numerical method was developed to inversely design structure parameters of IBCC with “target” mechanical properties using genetic algorithm. The novel lattice structure exhibits superior stiffness and energy absorption than conventional BCC (body-centered cubic) and OCT (Octet) structures, under the same relative density. For example, IBCC shows a maximum 59% improvement (at ρ¯=9.60%) of stiffness, and a maximum 25% improvement (at ρ¯=7.40%) of SEA, with respect to OCT. Besides, the stress plateau of IBCC is more stable than OCT, even at relatively large compression strain. The superior mechanical response of the IBCC lattice structure is mainly ascribed to bio-inspired topological design and interaction effects of curved rods in the “V-shaped” region. Besides, the effectiveness of the proposed inverse design method is verified by three numerical cases. The proposed bio-inspired design strategy, mechanical enhancement mechanism, and customizable method will be helpful in expanding the prospects of lattice structures in future multifunctional application fields.

Experimental investigation on energy absorption capability of 3D-printed lattice structures: Effect of strut orientation

This experimental study aimed to investigate the effect of strut orientation in various lattice structures that were created using 3D printers on the energy absorption capabilities of the structures. The experiment involved producing three different lattice structures, namely a cube lattice with vertical and horizontal struts, an octet structure with horizontal and 45˚ angled struts, and a body-centered-cubic (BCC) lattice structure with horizontal, vertical, and 45˚ angled struts using the FDM method. Nylon filament mixed with chopped carbon fiber was utilized as filament, and each lattice structure was designed to contain three units in the x and y directions and one and three units in the z-direction. The study conducted axial crushing tests on single-layer and three-layer lattices to determine the energy absorption capabilities of the various lattice structures. The octet lattice demonstrated the highest energy absorption in both single-layer and three-layer samples, making it the most efficient sample. In single-layer lattice samples, the cube and octet structures absorbed 77% and 94% more energy than the BCC structure, which absorbed only 12.8 J. However, the cube structure demonstrated the lowest energy absorption in three-layer samples. This was attributed to the buckling behavior seen in the strut of the lattice structure under axial load. The octet structure had the highest specific energy absorption value in both layers, making it the most energy-efficient sample.

Effect of B2 nanoprecipitates on mechanical behavior of TiZrNbVAl lightweight high entropy alloys upon dynamic loading

The addition of B2 nanoprecipitates provides a new way to improve the mechanical properties of lightweight high entropy alloys (LHEAs) with body-centered-cubic (BCC) structure. However, the study of B2 nanoprecipitates on BCC-LHEAs is limited to quasi-static tension. In this work, TiZrNbVAl LHEAs with BCC structure was chosen as model alloys and the effect of B2 nanoprecipitates on dynamic mechanical properties of TiZrNbVAl LHEAs was studied. The results show that the introduction of B2 nanoprecipitates not only significantly improves the dynamic strength, but also increases the plasticity from 31 % to more than 46 %, with an increase of more than 48 %. Microstructure evolution proves that during the plastic deformation process, the B2 nanoprecipitates promoted a large number of “second-generation bands” of dislocation in the separation of the first-generation bands, which effectively extended the plastic deformation region to the entire sample and improved the uniform deformation ability of LHEAs. Our results provide a solution for improving the mechanical properties of LHEAs under dynamic/impact conditions.

Design and Development of Ti–Zr–Nb–Ta–Ag High Entropy Alloy for Bioimplant Applications

A new non‐equiatomic 35Ti–35Zr–20Nb–5Ta–5Ag at% high entropy alloy (HEA) is designed by combining the HEA concept with the properties required for bioimplants. Mechanical alloying is used to synthesize the HEA, which is then compacted at 550 and 700 MPa and sintered at 1300 °C. The phases, microstructure, and mechanical properties are investigated, and in vitro corrosion properties are studied in a simulated body fluid. After 20 h of mechanical alloying, a single body‐centered cubic (BCC) phase with a nanocrystalline size of 3.6 nm was formed. After sintering, the microstructure is composed of dual‐phase BCC structures: the major BCC 1 phase, the grain boundary BCC 2 phase, and the ultra‐fine equiaxed phase. The results of the micro‐indentation test indicate that the elastic modulus of the HEA is 84.4 ± 8.7 and 113.2 ± 13.36 GPa, and its Vickers microhardness is 3.47 ± 0.1 and 5.35 ± 0.2 GPa when it was compacted at 550 and 700 MPa respectively. The corrosion resistance tests reveal that HEA compacted at 700 MPa has higher corrosion resistance than commercial Ti6Al4V alloy. The developed Ti–Zr–Nb–Ta–Ag HEA has improved corrosion resistance and a lower elastic modulus, making it a potential candidate for bioimplant applications.

Mechanical Properties of Lattice Structures with a Central Cube: Experiments and Simulations.

In this study, a new structure is proposed based on the body-centered cubic (BCC) lattice structure by adding a cubic truss in the center of the BCC structure and denoting it TLC (truss-lattice-cube). The different dimensions of the central cube can notably affect the mechanical properties of the lattice structure. With a fixed length (15 mm) of a unit cell, the optimal size for the central cube is determined to be 5 mm. Quasi-static compressive tests are performed on specimens made of polylactic acid (PLA) using additive manufacturing technology. The deformation characteristics of the new structure are analyzed in detail by experiments and numerical simulations. Compared to the BCC structure, the mechanical properties of the TLC structure were significantly improved. The initial flow stress of the TLC increased by 122% at a strain of 0.1; the specific strength enhanced by 293% at a strain of 0.5; and the specific energy absorption improved by 312% at a strain of 0.6. Printing defects in the lattice structure may remarkably damage its mechanical properties. In this work, incorporation of microcracks into the finite element model allows the simulation to capture the influence of printing defects and significantly improve the predictive accuracy of the simulation.

Magnetic Supramolecular Spherical Arrays: Direct Formation of Micellar Cubic Mesophase by Lanthanide Metallomesogens with 7-Coordination Geometry.

Here, an unprecedented phenomenon in which 7-coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H2O molecules, form micellar cubic mesophases at room temperature, creating body-centered cubic (BCC)-type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self-assembling behavior of 6-coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7-coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

A partially hollow BCC lattice structure with capsule-shaped cavities for enhancing load-bearing and energy absorption properties

Lattice structures have gained larger design space and wider application in aerospace, automobile, civil and other engineering fields due to the advancements in additive manufacturing (AM) technology. Seeking the optimal lattice structure configuration for the purpose of enhancing mechanical performance holds paramount importance. The hollow lattice structure possesses high material utilization efficiency, but often suffers from premature failure at the node interconnections. In this paper we propose a partially hollow lattice structure (PHBCC) with solidified nodes and capsule-shaped cavities in the middle of truss components. Quasi-static compression tests were performed on the partially hollow body-centered cubic (BCC) lattices manufactured via selective laser melting technology (SLM). The effects of various geometric parameters were analyzed through finite element simulations. The findings demonstrate that the introduced PHBCC lattice exhibits enhanced mechanical properties. Specifically, there is an observed increase of 92%, 51.9%, and 22.8% in terms of specific stiffness, specific strength, and specific energy absorption, respectively, in comparison to the conventional BCC and hollow BCC (HBCC) structure. Notably, the proposed PHBCC lattice displays superior energy absorption capacity compared to a majority of existing lattice structures.

High-pressure phase transitions in a laser directed energy deposited Fe-33Cu Alloy

Additively manufactured Fe-Cu alloys contain both equilibrium face-centered cubic (FCC) and metastable body-centered cubic (BCC) crystal structure Cu precipitates depending on their size. However, the stability of these nanoscale precipitates under extreme conditions such as high pressures has not been reported. This study investigates the phase transformations and microstructural stability of laser directed energy deposition (DED-LB) made Fe67Cu33 alloy (nominal composition in at.%) under high static pressure deformation using in-situ synchrotron X-ray diffraction under pressure, postmortem high-resolution scanning transmission electron microscopy (HR-STEM), and molecular dynamics (MD) simulations. In-situ XRD results reveal a reversible phase transformation from BCC to the hexagonal close-packed (HCP) structure in the Fe grains at an onset pressure of 16.4 GPa, significantly higher than reported in the literature for pure Fe. Although no high-pressure phase transition was observed in the FCC Cu grains through XRD, HR-STEM analysis uncovers a phase transition to the HCP structure in nanoscale metastable BCC Cu precipitates within the BCC Fe matrix. After decompression, the Fe matrix reverted back to the BCC structure with periodic lath martensite, while regions of the nanoscale BCC Cu precipitates retained the metastable HCP structure. MD simulations support the BCC → HCP transition in the embedded nanoscale coherent Cu precipitates, consistent with the classical Burgers mechanism. Thus, by leveraging in-situ XRD observation, postmortem high-resolution S/TEM microscopy, and MD simulations, this study offers profound insights into the distinctive phase transformations induced by high pressure in DED-LB Fe67Cu33 alloy, which is distinguished by its hierarchical microstructure.

A combined EBSD and machine learning study of predicting deformation twinning in BCC Fe81Ga19 alloy

Compared to face-centered cubic (FCC) metals, body-centered cubic (BCC) metals demonstrate more intricate deformation behavior and microstructural characteristics because of the influence of intrinsic unstable stacking faults and defect structure. To investigate the unique phenomenon of deformation twinning in Fe81Ga19 alloy with BCC structure at moderate temperature and low strain rate, four twin nucleation models were constructed using a combination of electron backscatter diffraction (EBSD) technique and machine learning. These models are aimed to predict twin nucleation of grains and explore the relationship between twin nucleation and microstructural attributes. The study revealed that amongst the 235 grains analyzed during in-situ compressive deformation, 32 grains experienced twinning. Nine attributes influencing twin nucleation were selected and ranked according to their importance. Grain area, average image quality, neighboring grain count, and the Schmid factor of twinning systems exhibited significant influence on twin nucleation. Decision tree and tree ensemble (XGBoost) achieved 94% and 96% accuracy, respectively, on the test set, showcasing robust generalization capability. Due to the optimization of hyperparameters, support vector machine (SVM) and artificial neural network (ANN) exhibited outstanding performance. The ANN model achieved an accuracy of 97% and an F1 score of 0.91 on the test set, while the SVM model achieved an accuracy of 98% and an F1 score of 0.94, indicating superior performance. Furthermore, the study revealed that the twinning stress in Fe81Ga19 alloy exhibited weak responsiveness to temperature during deformation, and the intrinsic factors of grains were identified as crucial factors influencing twin nucleation.

Mechanical alloying of AlCoCrFe and AlCoCrFeNi: Design and experimental evaluation of medium- and high-entropy alloy particles for cold spraying

The manufacturability of equiatomic high-entropy alloy (HEA) particles with single- and dual-phase crystal structures using the high-energy mechanical alloying (HE-MA) method was explored in this study. Following a material design-of-experiment (DoE) curriculum, particles were synthesized in a planetary mill. Milling times varied while operating under two distinct HE-MA manufacturing regimes: the conventional approach (simultaneous milling of constituent elements) and the sequential method (progressive milling with the introduction of elements in a specific order). Within the conventional regime, equiatomic AlCoCrFe and AlCoCrFeNi blends were milled, focusing on the influence of incorporating nickel (Ni) as a transient element into the base composition. This led to an equivalent particle size distribution ranging from 5 to 100 μm. Notably, the presence of Ni resulted in an increased fraction of the face-centered cubic (FCC) phase, coupled with a simultaneous reduction in grain and crystallite sizes, thereby enhancing the overall material strength. This knowledge was applied to the design and synthesis of a target equiatomic FeNiCoCrAl HEA system. In this context, individual elements were added to the starting/milled Fe + Ni alloy at four-hour intervals, in line with the sequential milling regimen. The results showed an interesting evolution: the conventionally milled AlCoCrFeNi particles exhibited a dual-phase body-centered cubic (BCC) and FCC structure, with a composition of 55% BCC and 45% FCC phase fractions, while the sequentially milled FeNiCoCrAl particles demonstrated a single-phase BCC structure after 24 h of milling.

Effects of structure parameters on performances of laser powder bed fusion processed AlSi10Mg body-centered cubic lattices

The study aims to explore the impact of structural parameters on the formability, mechanical properties, and heat conductivity of body centered cubic (BCC) lattice structures produced through laser powder bed fusion (LPBF). The BCC lattice structures with varied cell diameters and cell sizes were fabricated using LPBF. Surface morphologies, compression properties, and numerical simulation of heat transfer were carried out. Results indicated that the relative density of the BCC structure was influenced by the diameter and size of the cell. An increase in the diameter or a decrease in the size of the cell led to an increase in the relative density of the BCC lattice structure. However, the surface forming quality decreased. On the other hand, the compressive strength of the structure increased, and the heat transfer property was also enhanced. The BCC lattice structure achieved its highest relative density and obtained a peak compressive strength of 320.66 MPa when the cell rod diameter was 1.5 mm and the cell size was 3 mm.

The microstructure, mechanical compression, and electrochemical behavior of novel equiatomic CoCrMoNiW and Co-rich Co50Cr12.5Mo12.5Ni12.5W12.5 high-entropy alloys fabricated by vacuum arc remelting

In this research, we developed and analyzed novel equiatomic CoCrMoNiW and Co-rich Co50Cr12.5Mo12.5Ni12.5W12.5 high-entropy alloys (HEAs). Using FactSage, we identified dual face-centered cubic (FCC) and body-centered cubic (BCC) phases in the equiatomic HEA and a predominant FCC phase in the Co-rich HEA. The results of an elemental analysis reveal the significant presence of W and Mo in the equiatomic HEA and Co, Cr, and Ni in the Co-rich HEA. X-ray diffraction revealed dual-phase FCC and BCC structures in both HEAs, with the presence of an intermetallic μ phase. The Co-rich HEA exhibited significant compressive strain due to the prevalence of the ductile FCC phase at the expense of corrosion resistance. On the other hand, the CoCrMoNiW HEA demonstrated superior corrosion resistance comparable to those of the L605 alloy and 316 L stainless steel.

Unraveling influence of entropy on thermal stability and glass-forming ability of (Fe, Co)–(Ta)–B amorphous alloys: Insights from local atomic structure simulated by ab initio molecular dynamics

The thermal stability, glass-forming ability (GFA), and local atomic structure of (Fe, Co)–(Ta)–B amorphous alloys with different entropy values were investigated by experiments and ab initio molecular dynamics simulations, and the effects of entropy were elaborated from the perspective of the local atomic structure. The experimental results show that crystallization temperature, activation energy for crystallization, and undercooling degree all rise with the increase of configurational entropy (ΔSconf) of the alloys, whereas the critical thickness for amorphous samples shows a weak correlation with the ΔSconf. The simulations indicate that the short-range orders of the amorphous alloys are all dominated by B-centered tri-capped trigonal prisms (TTPs) and bi-capped square Archimedean antiprisms, and Fe-/Co-centered deformed body-centered cubic structures (BCCs) and icosahedral-like structures (ICOs) mainly with covalent-like B–Fe/Co and metallic Fe/Co–Fe/Co bonds. The increase in the ΔSconf results in shortened bond lengths and strengthened interactions between the main atomic pairs and sluggish diffusion of the atoms, thereby leading to enhanced thermal stability of both the amorphous phases and alloy melts. The GFA of the alloys shows a strong correlation with the characteristics of the short-range orders but not the entropy. The alloy containing the lowest fractions of the TTPs and BCCs but considerable ICOs possesses the best GFA.

Effects of different cross-sections of Body Centered Cubic cells on pressure drop and heat transfer of additively manufactured heat sinks

In many industrial applications, heat loads management requires the design and production of compact heat exchangers which are expected to handle high thermal loads with acceptable pressure losses, while assuring good mechanical performances. These challenging targets can be achieved by filling the cavities where the cool/hot fluid circulates with lattice structures promoting the heat exchange between the fluid and the cavity boundaries. Such lattice structures can be only produced through Additive Manufacturing due to their high geometric complexity. Recent experimental investigations proved the effectiveness of some kinds of lattice structures having a circular cross section. Here the aerothermal behaviour of Body-Centred Cubic (BCC) lattice stagger arrays in a rectangular channel was experimentally investigated by considerably extending the previous studies to higher Reynolds numbers (up to 30′000) and to new types of lattice structures. Specifically, three new BCC structures having a cam-like, drop-like and elliptical cross section were explored in this work and compared against those having circular cross section. All the samples were manufactured by means of Laser Powder Bed Fusion and made from AlSi10Mg. At first, the heat exchangers were comprehensively characterized by means of optical non-destructive methods. Successively they were tested in a dedicated rig by imposing constant heat flux boundary conditions. The characteristics of the transitional or fully turbulent approaching flow to the test section are also reported thanks to dedicated flow field measurements performed by Particle Image Velocimetry. According to the obtained results, the BCC structure with the circular cross section of larger diameter is the most effective in terms of heat transfer, although it is largely penalized by the pressure losses. Similar heat transfer performances were achieved by the tapered cross section of elliptical shape with the advantage of a considerably lower friction factor. Pressure losses resulted almost identical for all the tapered cross sections but lower than those of the circular one having an equal frontal dimension. When considering the thermal performance factor the circular shape becomes unfavourable for Re>20′000, while the elliptical cross section is the best choice to efficiently promote heat transfer up to Re=30′000.