Metal Lattice Research Articles

Understanding the superior mechanical properties of hollow-strut metal lattice materials

Intricate hollow-strut metal lattice materials are an emerging class of novel metallic cellular materials enabled by additive manufacturing. This work shows that hollow-strut Ti-6Al-4V lattice materials are consistently stronger and stiffer (up to 60% better) than their solid-strut counterparts of the same relative density, both experimentally and through finite element analysis (FEA). The underlying reasons are investigated using analytical models derived from the Timoshenko-beam theory, which considers deformation by concurrent stretching, bending and shear, rather than the single-mode deformation mechanism assumed by the Gibson-Ashby model. Hollow-strut lattices exhibit higher resistance to bending than solid-strut lattices at the same strut length and relative density, thereby leading to increased strength and stiffness. Hollow-strut metal lattices offer an unusual option for lightweight designs, with better mechanical properties at the same or lower density than solid-strut metal lattices.

Detecting missing struts in metallic micro-lattices using high speed melt pool thermal monitoring

Metal lattices are an important class of cellular materials that offer great advantages by providing high-strength and lightweight structures as compared to bulk materials. Progress in additive manufacturing techniques has led to increased complexity in design and shape of produced objects and is greatly beneficial for the development of metallic lattice structures. However additive manufacturing of lattices suffers from unpredictable defect creation that can compromise mechanical integrity of lattice structure. Although post-build inspection techniques can provide quality assurance of the process, accurate assessment can be technically challenging, time consuming and costly. In this work, we investigate the use of high-speed measurements of thermal emission from the melt pool to identify defective individual struts formed with a missing bottom half in an otherwise fully built lattice structure produced with laser powder bed fusion. Surprisingly, results indicate lower photodiode signal, suggesting colder melt pool surface temperature, when printing struts with missing bottom half as compared to nominal struts. Additional thermographic imaging and multi-physics simulations reveal that the low photodiode signal is accompanied by presence of hot spatters carrying heat away from detection and continuous avalanche of powder on the melt pool. Based on these observations, a method was developed to identify defective individual struts with missing bottom half in full built lattices. This prediction approach provides valuable insights about part quality which are important for process qualification and illustrates the utility of melt pool thermal emission monitoring for identifying specific defects introduced by laser powder bed fusion.

Strut and sheet metal lattices produced via AM-assisted casting and powder bed fusion: A comparative study

Strut and sheet metal lattices produced via AM-assisted casting and powder bed fusion: A comparative study

Electron screening in palladium

The electron screening effect was studied in the 1H(7Li,α)4He, 1H(19F,αγ)16O and 2H(19F,p)20F nuclear reactions on two different hydrogen-containing palladium foils. In one of the targets we did not detect a large enhancement of the cross section due to electron screening, and in the second one we measured a high electron screening potential for all three reactions, up to an order of magnitude above the theoretical models. Contrary to the predictions given by the available theories, the data suggest that the reason behind this difference is linked to a dependence of the electron screening potential on the host's crystal lattice structure and the location of the target nuclei in the metallic lattice.

Experimental Investigations of the Influence of Filler Materials on the Dynamic Structural Behavior of a Lattice Structure Manufactured by PBF-LB/M

The powder bed fusion of metals using a laser beam (PBF-LB/M) enables the manufacture of geometrically complex structures, which is limited to a certain extent using conventional processes. Lightweight lattice structures produced by PBF-LB/M are suitable for filling hollow component spaces, replacing solid material for mass reduction, or supporting parts during the building process. By infiltrating the cavities of these lattice structures with a second, viscoelastic material, hybrid materials can be created and adapted to a desired application. The current literature mainly deals with the static mechanical properties of unfilled, metallic lattices. However, the second material and its effects on the dynamic properties, such as a change in the eigenfrequency or the damping against unwanted vibrations, have not been investigated experimentally. In this study, a body-centered cubic lattice structure was filled with various polymeric materials to examine their influence on the dynamic structural behavior. The geometrically identical lattices were integrated into a cantilever beam, fabricated from SS316L using PBF-LB/M. The dynamic structural behavior of the beams was compared before and after the filling. Experimental modal analyses with an impact hammer were carried out on the specimens to determine the change in their eigenfrequency, stiffness, and damping ratio from the frequency response function. The results showed that the filling materials have a significant influence on the damping properties of the hybrid material.

Effect of low dissolved oxygen concentration on the defects and composition of regenerated passive film of Ti-6Al-4V alloy under continuous wear.

Tribocorrosion is one of the most common forms of failure of biomedical titanium alloys. As the passive film of titanium alloys is highly dependent on oxygen conditions, the passivation behavior and the microstructure of the passive film of Ti-6Al-4V under tribocorrosion in 1 M HCl with a low dissolved oxygen concentration (DOC) were studied by means of electron probe microanalysis (EPMA), Ar-ion etched X-ray photoelectron spectroscopy (XPS), focused ion beam (FIB) milling and high resolution transmission electron microscopy (HRTEM). The results showed that the protective ability of the regenerated passive film decreased sharply under low DOC. Al and V ions dissolved in excess, and a large number of oxygen atoms entered the matrix, leading to internal oxidation. Structural characterization indicated that Ti atoms occupied more metal lattice points in the regenerated passive film and that the high dislocation density in the deformed layer caused by wear facilitated the diffusion of Al and V. Finally, the first-principles calculation showed that Al had the minimum vacancy formation energy.

Enhanced transverse magneto-optical Kerr effect using ferromagnetic metal perforated with nanopore arrays.

Enhancement of transverse magneto-optical Kerr effects (T-MOKEs) based on surface plasmon resonance has attracted wide attention because of their high sensing performance. Most studies, however, mainly focus on prism-based magnetoplasmonic structures or architectures that incorporate a noble metal lattice and ferromagnetic layer, hindering device fabrication, miniaturization, and integration into a microfluidic sensing configuration. Herein, we propose a single Co6Ag94 ferromagnetic-metal layer perforated with a square nanopore array system with a pronounced T-MOKE magnitude 51 times higher than that of a smooth film, and with potential to detect gaseous analytes. The proposed system is sufficient to detect gaseous media for early environmental monitoring and enables an accessible pathway for magneto-optical sensor design.

Surface functionalized 3D printed metal structures as next generation recyclable SERS substrates.

Combining the design flexibility and rapid prototyping capabilities of additive manufacturing with photocatalytic and plasmonic functionalities is promising for the development of next-generation SERS applications such as point of care diagnostics and in situ monitoring of chemical reactions in fuels and chemical processing. Laser powder bed fusion (LPBF) is a well-matured additive manufacturing technique which generates metallic structures through localised melting and joining of metal powders using a laser. LPBF reduces material wastage during manufacturing, is applicable to a wide range of metals and alloys, and allows printing of complex internal structures. This feature article elaborates the use of soot templating, chemical vapour deposition and electroless plating techniques for grafting plasmonic and semiconductor nanoparticles on the surface of LPBF manufactured metallic substrates. The capability to fabricate different types of intricate metallic lattices using additive manufacturing is demonstrated and technical challenges in their adequate functionalization are elaborated. The developed methodology allows tailoring of the substrate structure, composition, morphology, plasmonic and photocatalytic activities and thus unveils a new class of recyclable SERS substrates.

Review on the Solid-State Welding of Steels: Diffusion Bonding and Friction Stir Welding Processes

Solid-state welding (SSW) is a relatively new technique, and ongoing research is being performed to fulfill new design demands, deal with contemporary material advancements, and overcome welding defects associated with traditional welding techniques. This work provides an in-depth examination of the advancements in the solid-state welding of steels through diffusion bonding (DB) and friction stir welding (FSW). Considerable attention was given to DB of steel, which overcame the difficulties of segregation, cracking, and distortion stresses that are usually formed in liquid-phase welding techniques. The defects that affected DB included two types: two-dimensional defects of a metallic lattice, i.e., phases and grain boundaries, and three-dimensional defects, i.e., precipitation. FSW, on the other hand, was distinguishable by the use of relatively low heat input when compared to fusion welding processes such as tungsten inert gas (TIG), resulting in the formation of a limited heat-affected zone. Moreover, fine grain structures were formed in the FSW interface because of the stirring tool’s severe plastic deformation, which positively affected the strength, ductility, and toughness of the FSW joints. For instance, higher strength and ductility were reported in joints produced by FSW than in those produced by TIG. Nevertheless, the HAZ width of the specimens welded by FSW was approximately half the value of the HAZ width of the specimens welded by TIG. Some defects associated with FSW related to the diffusion of elements, such as C/Cr atoms, through the weld zone, which affected the local chemical composition due to the formation of rich/depleted regions of the diffused atoms. Moreover, the lack-of-fill defect may exist when inappropriate welding conditions are implemented. On the other hand, the stirring tool was subjected to extensive wear because of the high hardness values, which negatively affected the economical usage of the FSW process. A summary of the results is presented, along with recommendations for future studies aimed at addressing existing difficulties and advancing the solid-state technology for steel.

Damping and Mechanical Properties of Epoxy/316L Metallic Lattice Composites

The lattice structure was prepared by selective laser melting of 316L metal powder, and the epoxy was naturally infiltrated into the pores of the 316L metallic lattice structure. The epoxy/316L metallic lattice composites with integrated structure and function were prepared. Scanning electron microscopy was used to observe the microstructure of the epoxy/316L metallic lattice composites. The damping performance of the epoxy/316L metallic lattice composites were studied by modal measurement method. At the same time, the engineering stress-strain curve was obtained by a quasi-static compression experiment on a universal testing machine. The results show that the interface of epoxy and 316L metallic lattice is well bonded, and there are a few bubbles in the epoxy. The epoxy/316L metallic lattice composites have high damping characteristics with damping ratio over 10%. The energy absorption of epoxy/316L metallic lattice composites is as high as 68.32 MJ/m3, showing high energy absorption characteristics.

Performance of Gaensel Energy Group's Nikel Storage Cells: Case Study

Last January Gaensel Energy group acquired 30% of Protonstar, this acquisition allowed the further development of Nikel storage cells. The extraordinary property of this new generation of accumulators lies in the accumulation of energy and its releasing no longer depending upon electrochemical processes, but simply on the interaction at the metal lattice level, in this case the Nickel. To date, we are facing a third generation of accumulators, in fact from the Volta’s battery, called primary, the electrochemical cells called secondary, in use today, having the prerogative to be rechargeable. Any storage system currently used is based on three basic components showing electrochemical linkage, namely an anode, a cathode and an electrolyte.
 
 Received: 23 September 2022 / Accepted: 28 November 2022 / Published: 20 December 2022

SBH17: Benchmark Database of Barrier Heights for Dissociative Chemisorption on Transition Metal Surfaces.

Accurate barriers for rate controlling elementary reactions on metal surfaces are key to understanding, controlling, and predicting the rate of heterogeneously catalyzed processes. While barrier heights for gas phase reactions have been extensively benchmarked, dissociative chemisorption barriers for the reactions of molecules on metal surfaces have received much less attention. The first database called SBH10 and containing 10 entries was recently constructed based on the specific reaction parameter approach to density functional theory (SRP-DFT) and experimental results. We have now constructed a new and improved database (SBH17) containing 17 entries based on SRP-DFT and experiments. For this new SBH17 benchmark study, we have tested three algorithms (high, medium, and light) for calculating barrier heights for dissociative chemisorption on metals, which we have named for the amount of computational effort involved in their use. We test the performance of 14 density functionals at the GGA, GGA+vdW-DF, and meta-GGA rungs. Our results show that, in contrast with the previous SBH10 study where the BEEF-vdW-DF2 functional seemed to be most accurate, the workhorse functional PBE and the MS2 density functional are the most accurate of the GGA and meta-GGA functionals tested. Of the GGA+vdW functionals tested, the SRP32-vdW-DF1 functional is the most accurate. Additionally, we found that the medium algorithm is accurate enough for assessing the performance of the density functionals tested, while it avoids geometry optimizations of minimum barrier geometries for each density functional tested. The medium algorithm does require metal lattice constants and interlayer distances that are optimized separately for each functional. While these are avoided in the light algorithm, this algorithm is found not to give a reliable description of functional performance. The combination of relative ease of use and demonstrated reliability of the medium algorithm will likely pave the way for incorporation of the SBH17 database in larger databases used for testing new density functionals and electronic structure methods.

Grid-tree composite support structures for lattice parts in selective laser melting

Metal lattice structure has excellent mechanical properties to develop lightweight parts, and selective laser melting (SLM) makes it possible to construct complex lattice parts without molds. Support structures are required in SLM to remove heat away from the process and reduce geometrical distortions. However, traditional support structure generation methods have some problems, such as low generation efficiency, difficulty in the removal and not meeting the fabrication requirements of lattice parts. Therefore, this article proposes a grid-tree composite support structure generation algorithm for lattice parts. First, optimize the build orientation of the lattice parts considering the surface quality of functional features and the processability of lattice structures. Then, identify the frame’s overhang area and the point overhang of lattice structures. Finally, generate the grid-tree composite support structure for lattice parts. We conducted experiments to verify our approach and compare our method with three supports of Magics RP. Experimental results reveal that our method is effective in reducing support volume and warpage deformation.

Reactive laser synthesis of ultra-high-temperature ceramics HfC, ZrC, TiC, HfN, ZrN, and TiN for additive manufacturing

Ultra-high-temperature ceramics (UHTCs) are optimal structural materials for applications that require extreme high temperature resilience (Mp > 3000 °C), resistance to chemically aggressive environments, wear, and mechanical stress. Processing UHTCs with laser-based additive manufacturing (AM) has not been fully realized due to a variety of obstacles. In this work, selective laser reaction sintering techniques (SLRS) were investigated for the production near net-shape UHTC ceramics such as HfC, ZrC, TiC, HfN, ZrN, and TiN. Specifically, group IV transition metal and metal oxide precursor materials (<44 μm) were chemically converted and reaction-bonded into layers of UHTCs using single-step selective laser processing in 100 vol% CH4 or NH3 gas that might be compatible with prevailing powder bed fusion techniques. Conversion of either metals (Hf, Zr and Ti) or metal oxides (HfO2, ZrO2, and TiO2) particles was first investigated to examine reaction mechanisms and volume changes associated with SLRS of single-component precursor systems. SLRS processing of metal or metal oxide alone produced near stoichiometric UHTC phases and yields up to >99.9 wt% total for carbides and nitrides and during the rapid reactive in-situ processing scheme. However, for single-phase feedstocks, gas-solid reactivity induced volumetric changes (correlated with the stochiometry of the rocksalt-type UHTC carbide and nitride products) resulted in residual stresses and cracking in the model-AM product layer. To mitigate conversion-induced stresses of single-phase precursors, composite metal/metal oxide precursors were employed to compensate for the volume changes of either the metal (which expands during conversion) or the metal oxide precursor (which contracts). While conversion of the optimized composite materials produced HfC layers with as little as +0.9% volume change, results indicated interparticle adhesion must be optimized to obtain robust UHTC-AM layers. Computational models of carbon and nitrogen diffusion in host transition metal lattices corroborated experimental results where a progressive particle conversion might inhibit interparticle diffusion unless laser processing parameters are carefully optimized to favor reaction bonding over discrete particle conversion. While this method presents a host of processing considerations, we demonstrate how this reactive approach may be viable for the AM of numerous UHTC materials that are not readily produced using current methods.

Diffusion and redistribution of hydrogen atoms in the vicinity of localized deformation zones

The presence of hydrogen atoms in the lattice of polycrystalline metals can lead to hydrogen embrittlement. The diffusion of hydrogen atoms and formation of hydrides depend on several parameters such as the microstructure of the metal alloy, the presence of stress risers, and the applied loading condition. In this study, a non-local crystal plasticity finite element model is coupled with hydrogen diffusion equations to study the effects of such parameters on the stress-assisted diffusion of hydrogen atoms in zirconium polycrystals. The concentrations of hydrogen atoms in the lattice and dislocation trap sites under different scenarios are studied to deconvolute the effects of texture, microstructure, and applied strain on hydrogen diffusion. It is shown that the concentration of hydrogen in the lattice peaks in the vicinity of grain boundaries and most importantly, at the triple-junction points. It is further shown that in localized deformation zones, such as twin or notch tips where dislocations concentrate, the effects of trapped hydrogen content can be significant.

A Hybrid Model Based on Jensen’s Inequality Theory for 3D Printed Lattice Structures Maximum Stress Prediction

Inherent defects in 3D-printed metal lattice structures are inevitable and significantly affect the structural part’s maximum stress. To solve this problem, a hybrid model based on Jensen’s Inequality Theory to predict the maximum stress of 3D printed lattice structures is proposed in this study. Jensen’s inequality theory means that the average of the model predictions will not be lower than the predictions of the individual prediction models. Therefore, the optimal number of hybrid models is discussed and designed, and the optimal base estimators are trained and selected on the same dataset. A hyperparametric approach is used to optimise the base estimator parameters. The experimental results demonstrate that the hybrid model performs better than a single estimator’s prediction, with an R2 of 0.83. This research offers a novel approach for the prediction of 3D-printed lattice structures using machine learning.

Hydrogen induced structural phase transformation in ScNiSn-based intermetallic hydride characterized by experimental and computational studies

Understanding an interrelation between the structure, chemical composition and hydrogenation properties of intermetallic hydrides is crucial for the improvement of their hydrogen storage performance. Ability to form the hydrides and to tune the thermodynamics and kinetics of their interaction with hydrogen is related to their chemical composition. Some features of the metal–hydrogen interactions remain however poorly studied, including chemistry of Sc-containing hydrides. ZrNiAl-type ScNiSn-based intermetallic hydride has been probed in the present work using a broad range of experimental techniques including Synchrotron and Neutron Powder Diffraction, 119Sn Möessbauer Spectroscopy, hydrogenation at pressures reaching several kbar H2 and hydrogen Thermal Desorption Spectroscopy studies. Computational DFT calculations have been furthermore performed. This allowed to establish the mechanism of the phase-structural transformation and electronic structure changes causing a unique contraction of the metal lattice of intermetallic alloy and the formation of the ...H-Ni-H-Ni… chains in the structure with H atoms carrying a partial negative charge. Such hydrogen absorption accompanied by a formation of a covalent Ni-H bonding and causing an unusual behavior contracts to the conventionally observed bonding mechanism of hydrogen in metals as based on the metallic bonding frequently accompanied by a jumping diffusion movement of the inserted H atoms – in contrast to the directional Metal-Hydrogen bonding observed in the present work. At high applied pressures ScNiSnH0.83 orthorhombic TiNiSi type hydride is formed with H atoms filling Sc3Ni tetrahedra. Finally, this study shows that scandium closely resembles the behavior of the heavy rare earth metal holmium.

Development of a statistical model for calculating the carbon diffusion parameters in iron and steels

Carbon diffusion in metals has received a lot of attention and has been the subject of intensive theoretical investigations in recent years. The purpose of this work is development a simple statistical model of the carbon atoms diffusion in the crystal lattice of metals and its application for calculating the diffusion coefficients of carbon atoms in iron and steel. The relationship between the diffusion flux of atoms and the gradient of their chemical potential, as required by non-equilibrium thermodynamics, is obtained from the basic principles of statistical thermodynamics. For a real solid solution of impurity atoms in a metal, an expression is found for the diffusion coefficient, the value of which depends on physical constants, the atomic weight of the solute, the square of the temperature and activity i-element in solid solution. The calculations have a good agreement with the known experimental data on the diffusion of carbon atoms in iron and steels and is higher than in classical atomic diffusion models. The activation energy of carbon diffusion in γ- phase of various steels has values close to 120 kJ. Proposed formula well describes the deviation of the carbon diffusion coefficient from the Arrhenius law at medium and high temperature.

Performance of chocolate bar-shaped modular thermal management system combined metal lattice liquid-cooling plate with paraffin in high-rate discharge

A chocolate bar-shaped hybrid battery thermal management system combined with a metal lattice liquid-cooling plate with paraffin has been proposed to improve the severe temperature rise and inhomogeneity of the prismatic lithium-ion battery at a high discharge rate. The cooling capabilities of different liquid-cooling tube arrangements of a prismatic battery have been compared, and the impacts of coolant flow rate, the metal lattice porosity and the liquid-cooling tube wall thickness on the cell's heat dissipation behaviour in various systems have been investigated. Multi-objective optimization has been conducted to obtain the optimal structural parameters of the system. The results indicate that the parallel arrangement of liquid-cooling tubes can ensure an excellent cooling capacity and a low system mass. The metal lattice plate with phase change material has a most outstanding cooling performance and highest mass group efficiency than other hybrid cooling systems. The highest temperature, temperature difference and the system's group efficiency will decline with the metal lattice's porosity decrease. The cooling capability of the system will be affected by the increased wall thickness of the LCT due to the balanced effect of the flow rate increase and thermal resistance. Under the optimal parameter combination, the module's highest temperature, temperature difference and group efficiency are about 44.95 °C, 4.35 °C and 78.98 % in 3C high-rate discharge, respectively.

Magnetic phase transition in an amorphous alloy: The theory of random fields of exchange interaction

In this study, an attempt was made to sequentially calculate the Curie temperature of iron-containing alloys based on the theory of random fields of exchange interaction. This method makes it possible to determine the conditions for the occurrence of ferromagnetism in an amorphous alloy depending on the concentration of exchange-interacting ions, their Holschmidt radius, and the type of crystal lattice of the transition metal.