Atomic Packing Research Articles

Pressure-induced structural variations and mechanical behavior of silicate glasses: Role of aluminum and sodium

This study investigates the effects of pressure-induced densification on the structural and mechanical properties of albite-like (12.5 % Na2O·12.5 % Al2O3·75 % SiO2) and sodium silicate (12.5 % Na2O·87.5 % SiO2) glasses using Molecular Dynamics simulations. Densification increased the coordination numbers of Al and Na, facilitated Al-O-Al clustering and formation of three-bridging oxygens, reduced T-O-T angles, and packed sodium ions in albite glass. Sodium silicate glass exhibited densification primarily through increased Na coordination, reduction of Si-O-Si angle and reduced Na-Na distances. Elastic modulus calculations revealed increased stiffness with densification due to enhanced atomic packing and glass reticulation. Uniaxial tensile tests showed densified glasses had higher ductility and strength than undensified counterparts, highlighting the positive effects of pressure-induced structural rearrangements. Hydrostatic compression tests demonstrated reversible densification under varying pressure loads, with pre-treatment conditions significantly affecting residual densification.

Short and medium range order in the rapidly solidified metallic liquid Ta: Atomic packing, connection modes, and pressure effect

In this study, molecular dynamics (MD) simulations were utilized to explore the Short and Medium-Range Order (MRO) in the rapidly solidified metallic liquid tantalum (Ta). Radial distribution function (RDF) and Voronoi tessellation analysis (VTA) techniques were employed to thoroughly explore the effect of pressure on the connectivity and structural properties at the Short-Range Order (SRO) and MRO levels. Our findings indicate that, at a quenching rate of 1013 K s-1, glassy states are achieved at or below 20 GPa, while crystalline phases emerge at 25 GPa. VTA analysis indicates a significant alteration in the local structure of glassy Ta with increasing pressure. Specifically, the fraction of icosahedral-like clusters decreases while the fraction of crystal-like clusters rises notably.Furthermore, we highlight that icosahedral-like clusters strongly tend to form 3-atom connection mode, while crystal-like clusters prefer 2-atom and 4-atom connection modes. Notably, icosahedral-like clusters are identified as the primary contributors to the emergence of the left sub-peak in the second peak of the RDF. In contrast, all cluster types contribute to the appearance of the right sub-peak.

Machine Learning-Based Investigation of Atomic Packing Effects: Chemical Pressures at the Extremes of Intermetallic Complexity.

Intermetallic phases represent a domain of emergent behavior, in which atoms with packing and electronic preferences can combine into complex geometrical arrangements whose long-range order involves repeat patterns containing thousands of atoms or is incompatible with a 3D unit cell. The formation of such arrangements points to unexplained driving forces within these systems that, if understood, could be harnessed in the design of new metallic materials. DFT-chemical pressure (CP) analysis has emerged as an approach to visualize how atomic packing tensions within simpler crystal structures can drive this complexity and create potential functionality. However, the applications of this method have hitherto been limited in scope by its dependence on resource-intensive electronic structure calculations. In this Article, we develop machine learning (ML)-based implementation of the CP approach, drawing on the collection of DFT-CP schemes in the Intermetallic Reactivity Database. We illustrate the method with comparisons of ML-CP and DFT-CP schemes for a series of examples, before demonstrating its application with an exploration of one of the quintessential instances of complexity in intermetallic chemistry, Mg2Al3, whose high-temperature unit cell is a 2.8 nm cube containing 1227 atoms. An analysis of its ML-CP-derived interatomic pressures traces the origins of the structure to simple matching rules for the assembly of Frank-Kasper polyhedra. The ML-CP model can be immediately employed on other intermetallic systems, through either its web interface or a command-line version, with just a crystallographic information file.

Enhancing structural strength and microwave dielectric properties of the Ba4(Sm1-xCex)9.33Ti18O54 ceramics

Herein, microwave dielectric ceramics of the Ba4Sm9.33Ti18O54 ceramics are substituted at A sites by partially replacing Sm at A1 sites with Ce, and the effects of ionic substitution at A sites on ceramic crystal structure and microwave dielectric properties are investigated. The Ba4(Sm1-xCex)9.33Ti18O54 (BSCT) ceramics prepared through the solid phase method has a typical tungsten–bronze structure, and its lattice spacing increases gradually with the increase in Ce content x. This increase is reflected in the increase in the cell volume and growth of ceramic grains. However, the excess Ce after Ce content exceeds 0.25 leads to the growth of ceramic grains and increase in porosity between grains, which in turn increases the dielectric loss of the ceramic. Under optimal sintering conditions, the ceramic crystal has a maximum atomic packing density of x = 0.25, which corresponds to its most stable structural properties, and the highest Q × f value of 9013 GHz. Raman spectroscopy results indicate that in titanium oxygen octahedrons, an increase in Ce substitution can effectively weaken the bending and tensile vibration intensities of titanium oxygen bonds, further enhancing structural strength.

Formation and strengthening mechanism of ordered interstitial complexes in multi-principle element alloys

Ordered interstitial complexes (OIC) are in the intermediate state between random interstitial solutes and chemical compounds, which can effectively improve the mechanical performance of multi-principle element alloys. Nevertheless, experimentally observing the complex atomic details of OIC formation and their interaction with dislocations remains challenging. Meanwhile, simulations of the OIC behavior faced the dilemma of lacking interatomic potentials for multi-component systems. In this work, we investigate the oxygen OICs in TiNbZr medium entropy alloys as a typical example to elucidate the strengthening and toughening mechanisms of OICs with a developed highly accurate deep learning potential. The formation mechanism, atomic packing of OICs and their interaction with dislocations, were then elucidated by molecular dynamics simulations with the developed potential. The interstitial atoms were found to aggregate energetically and increase the barrier of dislocation movement upon loading. It was found that the Nb content exerts a significant influence on the morphology and distribution of OICs. The decrease of Nb content favors the formation of larger cluster-like OICs. The existence of OICs can remarkably enhance the critical shear stress required for continuous dislocation movement. A pinning-cutting behavior was observed when an edge dislocation encounters an OIC, while a cross-slip behavior occurred when a screw dislocation encounters an OIC. The developed interatomic potential provides a valuable tool for elucidating the deformation mechanisms of TiNbZrO alloys, which highlights the significant effects of OICs on the mechanical performance of multi-principle element alloys.

Radiation-induced Fe segregation in the dual-phase FeCrNiMnAl high-entropy alloy under high-dose helium ion irradiation

This study investigates the radiation-induced Fe segregation in the dual-phase FeCrNiMnAl high-entropy alloy (HEA) under the helium (He) ion irradiation with a dose of 5 × 1017 ions/cm2. The superior bubble swelling resistance of the chemical-ordered NiAlMn phase with B2 structure is observed compared to the FCC FeCrMn matrix, which can be attributed to their differences in atomic packing factors. Fe segregation at phase boundaries (PBs) is detected after irradiation, as evidenced by a higher concentration of Fe at PBs than in the matrix by about 10 at.%. This phenomenon can be ascribed to the migration of Fe interstitials induced by irradiation cascades and the punching mechanism during bubble growth. In essence, the Fe segregation in this study is driven by the radiation-enhanced diffusion and metastable state of FCC-structured FeCrMn with supersaturated Fe atoms. These insights provide theoretical foundations and innovative perspectives for the radiation-induced segregation (RIS) in HEAs.

Continuous polyamorphic transition in high-entropy metallic glass

Polyamorphic transition (PT) is a compelling and pivotal physical phenomenon in the field of glass and materials science. Understanding this transition is of scientific and technological significance, as it offers an important pathway for effectively tuning the structure and property of glasses. In contrast to the PT observed in conventional metallic glasses (MGs), which typically exhibit a pronounced first-order nature, herein we report a continuous PT (CPT) without first-order characteristics in high-entropy MGs (HEMGs) upon heating. This CPT behavior is featured by the continuous structural evolution at the atomic level and an increasing chemical concentration gradient with temperature, but no abrupt reduction in volume and energy. The continuous transformation is associated with the absence of local favorable structures and chemical heterogeneity caused by the high configurational entropy, which limits the distance and frequency of atomic diffusion. As a result of the CPT, numerous glass states can be generated, which provides an opportunity to understand the nature, atomic packing, formability, and properties of MGs. Moreover, this discovery highlights the implication of configurational entropy in exploring polyamorphic glasses with an identical composition but highly tunable structures and properties.

Influence of BaTiO3 substitution on structural and thermal response of lead borosilicate glass for ultrasonic applications

An extensive examination of the impact of BaTiO3 doping on the mechanical and thermal characteristics of lead-borosilicate glasses is provided in this work. The glass density increases noticeably (from 6020 for BaTiO3 to 2533 kg/m3 for SiO2), and the molar volume decreases, suggesting a denser and more compact structural arrangement. The mechanical properties exhibited a notable improvement upon the addition of BaTiO3. Specifically, the longitudinal ultrasonic velocity (VL) increased from 3927 to 4458 m/s, and the shear velocity (VS) increased from 2317 to 2630 m/s, indicating a reinforced glass network. The bulk modulus increased from 35.71 to 58.06 GPa, and Young’s modulus increased from 57.2 to 92.98 GPa. These significant increases in elastic moduli were attributed to tighter atom packing and higher levels of cross-linking within the glass matrix. Furthermore, the glass structure’s increased rigidity and connectedness were further indicated by the Debye temperature (θD), which increased from 296.8 to 347.3 K. The influence of BaTiO3 on the thermal analysis is demonstrated, which revealed that increasing BaTiO3 content raises both the glass transition and crystallization temperatures. The results of the experiment demonstrate how much BaTiO3 doping can improve the physical characteristics of lead-borosilicate glasses, enabling them to be used in sophisticated optical and structural applications.

Molecular dynamics simulations study on structure and mechanical properties of Na2O–CaO-Al2O3-B2O3-SiO2 glasses with different Al2O3/B2O3 ratio

The structure and mechanical properties of Na2O–CaO-Al2O3-B2O3-SiO2 glass were simulated using molecular dynamics simulations, with Al2O3 replacing B2O3. The simulated elastic modulus (E) increases while the fracture toughness (KIc) decreases, consistent with the experimental findings. The increase in Al2O3/B2O3 enhances the proportion of [AlO4] in the glass network, while reducing the proportion of [BO4] and [BO3], thereby increasing dissociation energy and atomic packing density, ultimately improving the E of the glass. The fracture process of glasses involves both elastic and plastic deformations. Elastic deformation primarily includes bond length extension, bond angle bending, and changes in coordination numbers of Ca2+ and Na+. Plastic deformation primarily results from changes in coordination numbers of B3+ and Al3+ during stretching, with reduced [BO3] and [BO4] decreasing the plastic region and subsequently reducing KIc. This study will provide a theoretical basis for adjusting E and KIc values for aluminoborosilicate glass.

Impact of atomic packing and electronic structure on icosahedral short-range order and glass-forming ability of Zr–Cu metallic glasses

ABSTRACT Chemical and topological short-range ordering are important for glass formation in metallic alloys. Yet, it remains little understood from the viewpoint of the electronic bonding among the constituent elements of the alloys. In this work, we study CuxZr100−x, (46 ≤ x ≤ 70) metallic glasses, where the atomic packing efficiency and the electronic structure of the full icosahedra, the key short-range order structures, have been investigated in detail. To capture a realistic picture of the electronic bonding in the icosahedra in the as-quenched metastable state, DFT study of the electronic structure of the icosahedra extracted from classical molecular dynamics simulation is carried out. Results for the CunZr13−n , (4 ≤ n ≤ 9) clusters reveal that Cu6Zr7, Cu7Zr6 and Cu8Zr5 are the most abundant, electronically stable in Cu50Zr50 , Cu58Zr42 and Cu64Zr36, respectively. These three clusters also exhibit pseudo-gap in the density of states at the Fermi level – a feature linked with glass-forming ability according to the nearly-free electron approach. The partial density of states demonstrates the effect of small changes in the stoichiometry of the clusters on the s, p and d states of Cu and Zr in Cu–Cu and Cu–Zr bonding and hence, the stability of the clusters.

Nearly close-packed atomic arrangements in BaTi2O5 glass

Recent advancements in glass synthesis have led to the creation of novel oxide glasses without tetrahedral corner-sharing networks. Of particular interest are glasses with high atomic packing densities, showcasing improved functionalities. Conventional analyses revealed the presence of not only four-coordinated polyhedra but also five- or six-coordinated polyhedra, which are connected via corner-sharing, edge-sharing, or face-sharing linkages. This study adapted the reduced atomic arrangement (RAA) method to analyze densely packed oxide glasses. The RAA method revealed a near-close-packed structure within a 10 Å range throughout BaTi2O5 glass, with Ba2+ and O2− ions arranged accordingly. Moreover, the structural model derived from relaxing the closest-packed arrangement via molecular dynamics simulations faithfully replicated the X-ray diffraction data. These findings suggest that minor deviations from the closest-packed atomic arrangement can initiate glass formation without corner-sharing tetrahedral networks. The RAA method proves highly effective in understanding glass formation mechanisms in unconventional oxide glasses.

Study of Size Effect on Ni60Nb40 Amorphous Particles and Thin Films by Molecular Dynamic Simulations

Ni60Nb40 amorphous particles (APs) and amorphous thin films (ATFs) with various sizes were investigated by molecular dynamic simulations. It is revealed that sample size has effects on both Ni60Nb40 APs and ATFs composed of shell or surface and core components. Ni60Nb40 APs have an average bond length of 2.57 Å with major fivefold-symmetry atomic packing and low bond-orientation orders of Q6 and Q4 in both core and shell components. Ni atoms in Ni60Nb40 APs and ATFs prefer to segregate to the shell and surface regions, respectively. Atomic packing structure differences between various-sized Ni60Nb40 APs and ATFs affect their glass transition temperatures Tg, i.e., Tg decreases as the particle size or the film thickness decreases in Ni60Nb40 APs and ATFs, respectively. Our obtained results for Ni60Nb40 APs and ATFs clearly reveal a size effect on atomic packing and glass transition temperature in low-dimensional metallic glass systems.

Exploring structural and optical properties of Cu-doped and Fe-doped sodium borate glasses

This study investigated the structural and optical properties of Cu-doped and Fe-doped sodium borate glasses. X-ray diffraction (XRD) patterns confirmed that both samples were amorphous, with no sharp peaks. However, differences in the width and center of the high-intensity humps suggested variations in atomic packing and field strength between the two samples. Fourier transform infrared (FTIR) spectra showed wider vibrational modes and stronger absorption in the Fe-doped sample, confirming its higher atomic packing and field strength. Luminescence spectra indicated that the Cu-doped sample had a higher ratio of Cu2+:Cu3+ than the Fe-doped sample of Fe2+:Fe3+, resulting in greater UV–visible region absorption. Optical parameters such as absorbance, transmittance, and reflectance supported these findings, with the Fe-doped sample exhibiting higher absorbance band edges. Quality factor (Q.F.) analysis revealed that the Fe-doped sample had a larger Q.F. than the Cu-doped sample, indicating lower energy losses. Furthermore, the optical conductivity of both samples increased with photon energy, with the Cu-doped sample dominating in all energy regions. Finally, both samples exhibited high effective atomic numbers, suggesting potential applications in radiation shielding, with the Cu-doped sample having a wider radiation shielding window. Finally, the findings unique structural and optical properties suggests the Cu-doped and Fe-doped sodium borate glasses to a lot of potential applications in various fields including radiation shielding, optics, electronics, and energy storage.

Crystal Structure, Infrared Reflection Spectrum, and Improved Microwave Dielectric Characteristics of Ba4Sm28/3Ti18O54 Ceramics via One-Step Reaction Sintering.

High-k Ba4Sm28/3Ti18O54 ceramics with improved microwave dielectric characteristics were successfully fabricated using the one-step reaction sintering (RS) route. The sintering characteristics, microstructure, crystal structure, infrared reflection spectrum, and microwave dielectric characteristics of Ba4Sm28/3Ti18O54 ceramics prepared by the RS route were systematically investigated. Samples prepared by the RS route exhibited single-phase orthorhombic tungsten-bronze structure and dense microstructure at optimum sintering temperature. Compared with the conventional solid-state (CS) process, the Ba4Sm28/3Ti18O54 ceramics fabricated by the RS route presented a smaller temperature coefficient (TCF), a higher quality factor (Q × f), and a higher permittivity (εr). The improved microwave dielectric characteristics were highly dependent on the theoretical permittivity, atomic packing fraction, suppression of Ti3+, and Ti-site bond valence. Excellent combined microwave dielectric characteristics (TCF = -7.9 ppm/°C, Q × f = 9519 GHz, εr = 80.26) were achieved for Ba4Sm28/3Ti18O54 ceramics prepared by RS route sintered at 1400 °C, suggesting the RS route was a straightforward, economical and effective route to prepare high-performance Ba4Sm28/3Ti18O54 ceramics with promising application potential.

Strain-dependent work function of metal surfaces: Insights from first-principles investigation

Establishing a fundamental understanding of the relationship between electronic work function (WF) and applied strain is crucial for the development flexible electrodes of and enhancement of metal corrosion resistance. The underlying mechanisms of this relationship have remained unknown, largely due to inconsistencies from previous studies caused by different strain states and the complex impact of anisotropic surface effects. In this study, we employ first-principles methods to investigate the work functions of strained metal surfaces. Our research findings suggest that lateral strain states significantly affect the WF, while strain perpendicular to the surface has minimal influence. Through subjecting the metal surface to linear elastic deformation, we establish a canonical relationship between the work function and strain. Further comparison of work functions under biaxial strain indicates that surfaces with high atom packing density exhibit greater susceptibility to strain. The mechanism behind the strain-dependent WF is attributed to the interplay of bulk electronic structure and surface dipole effects, which. These effects are influenced by volume changes and the redistributedion of charge density. To this end, we propose an effective strain-induced approach for engineering the WF of metal electrode is proposeds, with potential applications in other various materials.

Unraveling the complexity of Fe-based bulk metallic glasses: Insights into dynamic mechanical relaxation in atomic-scale

This research conducts a thorough investigation into the structural and mechanical evolution of Fe74B20Nb2Hf2Si2 bulk metallic glass (BMG) subjected to thermal aging. Utilizing X-ray diffraction (XRD) and selected area electron diffraction (SAED), the study verifies the amorphous structure of the as-cast BMG, highlighting evidence of short-range ordering (SRO). Thermal aging conducted between 342 and 570 K induces substantial changes, notably the formation of Fe23B6 and α-Fe phases and reduced defect concentrations. During dynamic mechanical analysis, a significant shift was observed, which is characterized by a decrease in the intensity of β-relaxation and an increase in β-activation energy from 333.3±2.1 kJ/mol (for the sample aged at 342 K) to 384.6±5.6 kJ/mol (for the sample aged at 570 K). Nanoindentation evaluations reveal an increase in hardness from 11.85±0.22 GPa (for the as-cast BMG) to 14.65±0.41 GPa (for the sample aged at 570 K), accompanied by an increase in Young’s modulus from 211.61±3.00–244.24±2.00 GPa. These changes imply tighter atomic packing and diminished free volume due to aging, suggesting an advanced stage of structural relaxation. Additionally, the material demonstrates a decrease in plastic strain from 0.0052 in its as-cast state to 0.0026 at 342 K, progressing to brittle behavior with further aging. This study shows the pivotal role of precise aging temperature control in optimizing BMGs for diverse applications, illustrating the intricate interplay between thermodynamics and kinetics in material science.

Navigating the 18-n+m Isomers of PdSn2: Chemical Pressure Relief through Isolobal Bonds and Main Group Clustering.

The 18-n electron-counting rule provides structural guidelines for electronically feasible transition metal (T)-main group (E) phases, contributing toward the goal of material design. However, the availability of numerous potential structure types at any electron count creates a challenge for the prediction of the preferred structures of specific compounds, as is illustrated by the concept of 18-n+m isomerism. In this Article, we explore the driving forces stabilizing one 18-n+m isomer over another with an analysis of the structure of PdSn2, a layered intergrowth of the fluorite and CuAl2 structure types. The DFT-reversed approximation Molecular Orbital (DFT-raMO) method reveals that PdSn2 and its hypothetical parent structures all adhere to bonding schemes approximating the electronic configurations expected from the 18-n rule, with various degrees of isolobal Pd-Pd bonding and Sn clustering. However, partial electron transfer between the Pd 5p orbitals to the Sn 5s orbitals contributes to the absence of convincing electronic pseudogaps near their Fermi energies. As such, there is no clear electronically driven preference among the structure types. This situation allows for atomic packing effects to prevail: DFT-Chemical Pressure (DFT-CP) analysis illustrates that in the fluorite-type parent structure, positive Pd-Sn CPs lead to overcompression of the Pd atoms and a stretching of the relatively open Sn sublattice. In contrast, in the CuAl2-type parent structure, Sn atoms cluster into tetrahedra, opening space for an expanded Pd environment and the formation of Pd-Pd interactions. However, the tetrahedral packing of the Sn atoms here leads to frustration between negative and positive Sn-Sn CPs. Through the development of the angular CP correlation function (CPcor+) as a tool to quantify frustration among interatomic interactions, we demonstrate how the observed PdSn2 structure balances these effects by tuning the degree of Sn-Sn clustering and expansion of the Pd environment. These observations point to generalizations for most 18-n+m isomers, where increased main group ligand clustering (+m) and isolobal bonds (+n) can accommodate compositions with different T and E atomic sizes.

Solid-state green synthesis of two (1:1) organic intermolecular compounds; their physico-chemical, thermal, single crystal growth, and atomic packing studies

The solid-state solvent free reaction method has been adopted for the one-pot synthesis of novel organic materials with utmost 100 % yield. To identify the composition forming the intermolecular compound (IMC), the solid-liquid equilibria of entire compositions have been studied by establishing the phase diagram of n, n-dimethylaminobenzaldehyde (DMAB) with anthranilamide (AN) and 2-chloro-4-nitro benzoic acid (CNBA). The structural changes and novelty of the IMCs to that of parents are studied using FTIR, NMR and X-ray diffraction. The studies of optical properties of intermolecular compounds using UV–vis absorption and fluorescence spectroscopy infer the significant fluorescence emission. The single crystals of both intermolecular compounds, ANDMAB and DMABCNBA, are grown from solution using slow evaporation technique. The single crystal X-ray diffraction studies reveal that IMC of AN and DMAB is a racemic mixture whereas IMC of DMAB and CNBA is a co-crystal, and both the crystals have crystallized in triclinic P1‾ space group. The thermal stability and thermal behaviors are also studied using the experimental heat of fusion values obtained from differential scanning calorimetry (DSC).

Microstructural stability and mechanical property of AlCrFeMoTi high-entropy amorphous alloy thin films under He+ ions irradiation

High-entropy amorphous materials have recently proved exceptional radiation resistance, showing potential as a candidate materials for nuclear industry applications. This study synthesized nearly equi-atomic AlCrFeMoTi high-entropy amorphous thin films with a thickness of about 499 nm using magnetron sputtering. The prepared films were subjected to low dose, 0.5 MeV He+ ion irradiation, with varying irradiation damage ranging from 0.01 to 0.1 displacement per atom (dpa). Increasing the irradiation dose led to a decrease in the radius of the inner diffraction halo (r) and an increase in the crystal-like order, indicating an irradiation-induced structural relaxation process within the amorphous matrix. This relaxation results in more efficient atomic packing, yielding a denser amorphous structure and enhanced hardness of AlCrFeMoTi high-entropy amorphous thin films. This study demonstrates that AlCrFeMoTi high-entropy amorphous thin films exhibit remarkable radiation resistance, with stable microstructure and mechanical properties under He+ irradiation, making them promising candidates for applications in the nuclear industry.

Complementary nanodomain structures in topologically close-packed precipitates of Al-Zn-Mg-Cu alloy

High-strength aluminium alloys attract continuous research interest, owing to their wide use in aerospace and terrestrial transportation industries. The performance of the alloys is essentially determined by nanoscale precipitates, thus understanding the structure and formation mechanism of the precipitates during thermal processing is of great importance. Here, we reveal complementary domain structures in precipitates in a high-strength Al-Zn-Mg-Cu alloy using a combination of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. Through the transfer of fivefold symmetry polyhedra at domain boundaries, the intermediate precipitates develop two sets of highly ordered and structurally complementary nanoscale domains in their nucleation and growth. This new type of atom packing maintains the topologically close-packed structure inside the precipitates while reducing the lattice misfit with the Al matrix and the barrier of structural transformations on two interfaces, demonstrating good thermal stability. Our discoveries lead to insight into the precipitate evolution in the Al-Zn-Mg-Cu alloy system and can help understand other precipitation processes of complex structured phases. Furthermore, the evolution process demonstrates an advanced mode of building metastable architectures with nanoscale interlocking pieces in alloy matrixes, which may inspire strategies to obtain high-strength, lightweight and thermostable alloys.