Structural Materials Research Articles

Anti-solvent materials enhanced structural and optical properties on ambiently fabricated perovskite thin films

Perovskite solar cells (PSCs) hold potential for low-cost, high-efficiency solar energy, but their sensitivity to moisture limits practical application. Current fabrication requires controlled environments, limiting mass production. Researchers aim to develop stable PSCs with longer lifetimes under ambient conditions. In this research work, we investigated the stability of perovskite films and solar cells fabricated and annealed in natural air using four different anti-solvents: toluene, ethyl acetate, diethyl ether, and chlorobenzene. Films (about 300 nm thick) were deposited via single-step spin-coating and subjected to ambient air-atmosphere for up to 30 days. We monitored changes in crystallinity, electrical properties, and optics over time. Results showed a gradual degradation in the films’ crystallinity, morphology, and electro-optical properties. Notably, films made with ethyl acetate exhibited superior stability compared to other solvents. These findings contribute to advancing stable and high-performance PSCs manufactured under normal ambient conditions. In addition, we also discuss the possible machine learning (ML) approach to our future work direction to optimize the materials structures, and synthesis process parameters for future high-efficient perovskite solar cells fabrication.

Ultrahigh strength and damage tolerance in a hierarchical-structured titanium alloy

Achieving damage tolerance in structural materials can be challenging due to the need for both high strength and ductility, which are typically incompatible properties. The common post-processing techniques in thermomechanical machining enable us to fabricate metal materials with distinctive microstructures, thereby enhancing the mechanical properties of the materials. We show that a hierarchical-structured titanium (HST) alloy consisting of belt-like α phase (αb), submicron-scaled oval α phase (αo), and nano-scaled secondary α phase (αs) has been designed by employing precision and user-friendly process routes. The hierarchical microstructure performs high strength while preserving respectable ductility. The ultrahigh strength (σYS∼1257 MPa and σUTS∼1411 MPa)) can be mainly attributed to the grain boundary strengthening served by hierarchical α phase. Moreover, the unique architecture provides excellent resistance to crack propagation, obtaining a large ductility (20%), making it a highly promising structural material for engineering applications.

Strong and Fatigue-Resistant Carbon Nanotube Composites Enabled by Amorphous/Crystalline Heterophase Shell.

Lightweight materials with high strength and long cyclic lifespan are greatly demanded in practical applications, yet these properties are usually mutually exclusive. Here, we present a strong, lightweight, highly deformation-tolerant, and fatigue-resistant carbon nanotube (CNT) composite enabled by an amorphous/crystalline heterophase carbon shell. In particular, we obtain nanocrystallites with CNT-induced crystalline orientation uniformly embedded within an amorphous matrix by controlled thermal annealing. The heterophase carbon shell effectively alleviates the stress concentration and inhibits crack propagation, which renders our composite superior mechanical properties and high fatigue resistance (106 compression cycles at 20% strain with high stress of 144 kPa, or 5 × 105 cycles at 50% strain with stress up to 260 kPa). This study provides a deep understanding of amorphous-crystalline phase transition and insight into utilizing phase engineering to design and develop other high-performance functional materials such as structural materials and catalysis.

Green and sustainable fabrication of DES-pretreated high-strength densified wood

Wood is a sustainable, benign, and high-performing green structural material readily available in nature that can be used to replace structural materials. However, insufficient mechanical performance (compared to metals and plastic), moisture sensitivity, and susceptibility to microorganism attack make it challenging to use wood as it is for advanced engineering applications. We here present an efficient approach to fabricating densified wood with minimal time and waste generation, demonstrating high mechanical strength, and decreased water penetration on the surface. Wood slabs were treated with deep eutectic solvents (DESs) to solubilize the lignin, followed by in-situ regeneration of dissolved lignin in the wood. Then, the slabs were densified with heat and pressure, turning the wood into a functionalized densified material. Lignin regeneration and morphological changes were observed via two-photon microscopy and Scanning Electron Microscopy (SEM), respectively. The final product is less susceptible to water absorption on the surface and has enhanced flexural strength (> 50% higher), surface hardness (100% increased), and minimal set recovery compared to natural wood. The improved mechanical performance is due to regenerated lignin which acts as a glue and fills spaces present within the interconnected cellulose network inside the wood, forming a highly dense composite during densification. Such enhancement in the properties of DES-densified wood composite makes it a favorable candidate for advanced structural and engineering applications.

Status and issues of high-temperature and high-pressure water corrosion research of fusion structural materials in Japanese DEMO reactor development

Abstract The activated corrosion product assessments of fusion structural materials are essential to designing components and evaluating workers’ radiation exposure. This paper first gives the R&D status of the high-temperature pressurized water corrosion study of reduced activation ferritic/martensitic steels and chromium–zirconium–copper (CuCrZr) alloys, which are the leading candidate materials of fusion reactor in-vessel components such as breeding blanket and divertor, which are utilized in high-temperature and high-pressure water, and the recent progress of corrosion test apparatus simulating the unique environment of a fusion reactor will also be presented.

Formation process, microstructure characterization, and evolution mechanism of adiabatic shear bands in U-5.7Nb alloy under dynamic deformation

Uranium-niobium (U-Nb) alloys as structural materials play an important role in nuclear industry. During their utilizing, U-Nb alloys tend to dynamically fracture along the adiabatic shear bands, which affects their performances. In order to understand the formation process and mechanisms, we systematically investigate the adiabatic shear bands formed in U-5.7Nb alloys, where systematical characterization methods were applied, such as optical microscope, scanning electron microscope, and high-resolution transmission electron microscope. Using stopper rings, the U-5.7Nb alloy was impacted by a split Hopkinson pressure bar at a strain rate of 8 000 s-1 to perform seven strain levels. The formation process of adiabatic shear bands in U-5.7Nb alloys was characterized, and we found two types of adiabatic shear bands: the deformed ones together with the transformed ones. They are formed at different stage of severe shear localization. The deformed adiabatic shear bands mainly included highly deformed and elongated grains, and the transformed adiabatic shear bands were basically composed of ultrafine equiaxed grains with size of about 150 nm. High density of dislocations or dislocation cells were found in these ultrafine equiaxed grains. The occurrence of ultrafine equiaxed grains in the adiabatic shear bands of U-5.7Nb alloys was deduced to be rotational dynamic recrystallization mechanism.

Improvement of gummy candy structure by gelling ingredients and cooling temperature

AbstractGummy candies achieve their widespread appeal through a unique textural profile. The combination of springiness, chewiness, and a potential initial hardness upon biting (depending on formulation) creates a multi‐sensory eating experience. The readily soluble sugars and other components contribute to the quick dissolution and ease of digestion. Therefore, we conducted research to develop gummy candies made from structural materials of gelatin combined with agar and maltose syrup and evaluated the effect of ingredient ratios on the candy's structural and sensory properties. Sweetener maltose syrup (DE = 42) and a suitable content of agar supplementary had a significant influence on the structure of the product (p < 0.05). The structure of gummy candies was analyzed by the structure measuring instrument TPA (structure profile analysis) combined with sensory evaluation. The process of manufacturing candy involves the melting and homogenization of all constituent ingredients, followed by a sequence of freezing and cool drying to complete the production. The most interesting candies were made with agar 0.5%, gelatin 10% (powdered gelatin with Bloom 250), saccharose 30%, maltose syrup 10%, citric acid 0.1%, and pure water before being chilled at 4 °C for 4 h. This property remained unchanged during the 6‐month storage period in anaerobically sealed packaging, at room temperature.

Research Progress on the Microstructure Evolution Mechanisms of Al-Mg Alloys by Severe Plastic Deformation.

Al-Mg alloys are widely used as important engineering structural materials in aerospace engineering, transportation systems, and structural constructions due to their low density, high specific strength, corrosion resistance, welding capability, fatigue strength, and cost-effectiveness. However, the conventional Al-Mg alloys can no longer fully satisfy the demands of practical production due to difficulties caused by many defects. The high strength of Al-Mg alloys as non-heat treatment precipitation-strengthened alloys is achieved primarily by solid solution strengthening along with work hardening rather than precipitation strengthening. Therefore, severe plastic deformation (SPD) techniques can be often used to produce ultrafine-grained structures to fabricate ultra-high strength aluminum alloys. However, this approach often achieves the strengthening of material at the cost of reduced ductility. This paper comprehensively summarizes the various approaches of ultrafine/nanocrystalline materials for enhancing their plasticity, elaborates on the creation of a bimodal microstructure within the alloy, and discusses the formation of a nanotwin microstructure within the alloy and the incorporation of dispersed nanoparticles. The mechanisms underlying both the strengthening and toughening during large plastic deformation in aluminum alloys are summarized, and the future research direction of high-performance ultrafine crystalline and nanocrystalline Al-Mg aluminum alloys is prospected.

Oxidation Behavior of a Novel Nickel-Based Alloy in Air and Steam at 1273 K for the Oxygen–Hydrogen Combustion Chamber

AbstractAs part of advancing oxygen–hydrogen combustion power generation technology, a study was carried out to evaluate the oxidation behavior of a novel developed Ni–Cr–W alloy as the structural material candidate. Tungsten is utilized in the alloy as a solid solution-strengthened element and as an α2-W precipitate former. The examination involved exposing the developed alloy and commercial alloys, Hastelloy X and Nimonic 263, to air and steam environments at 1273 K. The results show a different oxidation behavior of the developed alloy. Considering the air oxidation kinetics, the performance of the developed alloy was on par with that of Hastelloy X and superior to Nimonic 263. A single outer chromia scale was established with an intergranular oxide. Whereas steam exposure resulted in the formation of outer and inner chromia scales with a deeper intergranular oxide penetration. Thicker chromia formation with a lower mass gain indicates the evaporation of chromia under a steam atmosphere.

High strength low alloy steel joint fabricated by laser welding with real-time high-frequency resistance heating

The balance between softening and hardening is still a great challenge for the laser welding of the high strength low alloy steel. For example, welding with low heat input was commonly used to avoid softening, but it would inversely harden the joint and introduce the undesired welding defects such as hydrogen-induced cracks. This work proposed a simple and robust processing technique, denominated High Frequency electric cooperated Laser Welding. Laser heat source was combined with high-frequency electric heat source to balance heat input distribution and reconcile the contradiction between softening and hardening in the welding of high strength low alloy steel. As a structural material sensitive to welding softening and hardening, S690QL steel was adopted to show the fundamental advancement of the new process. Benefitted from the skin effect and proximity effect of high-frequency current that improve the heat input distribution and the regulation of the high-frequency heat input proportion, the martensite content in the heat affected zone was greatly reduced, whilst the grain size was limited to a low value. Under the high-frequency heat input proportion of 47.1 %, lower bainite distributed throughout the heat affected zone. The softening and hardening issues of the joint therefore have been improved simultaneously: the tensile strength of the joint was almost equal to that of the base material, the impact energy of weld seam and the heat affected zone reached 77.6 J and 66.2 J respectively.

Laboratory characterisation of sand-tyre mix as bedding material for buried structures

Bedding material directly interacts with buried structures and supports to sustain external loadings such as traffic and overburden soil pressure. Therefore, soil-structure interaction plays an essential role in the stability and safety of buried structures. In particular focusing on underground pipelines, the annual rate of failures in Australia is around 19 % per 100 km of pipeline and can cost millions of Australian dollars in maintenance. Of these annual failures, ground vibrations from heavy traffic and construction activities are a major cause. In order to reduce such effects of ground vibrations on buried structures, this paper presents the possible application of sand-rubber mixes as a bedding material, where rubber is sourced from recycled tyres. The performance of sand-tyre mixes with regard to the potential for vibration reduction is assessed through this experimental study which comprises of particle size distribution, standard proctor compaction, permeability test, direct shear test, California Bearing Ratio and Repeated Load Test. From these tests, it was found that sand mixed with up to 20 % recycled tyre rubber was the most suitable mix for use as a bedding material.

Improving the surface characteristics of metallic glass thin ribbons by laser gas nitriding

The single-roll cooling method excels in producing metallic glass ribbons (MGRs), offering rapid cooling rates and exceptional thickness consistency. Nevertheless, a large number of defects including micro-pits and micro-gaps usually appear on the surface of MGRs after the roll forming process, significantly impacting their service life and performance. Laser gas nitriding is a cutting-edge surface modification technology that has been extensively used to improve the comprehensive performance of various metal components. Herein, an attempt was made to simultaneously improve the surface quality and mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 MGRs by nanosecond pulsed laser irradiation in a flowing nitrogen atmosphere. The effects of laser irradiation parameters on the surface characteristics of the laser gas nitrided regions were systematically investigated. The experimental results showed that the surface quality of MGRs after laser gas nitriding was enhanced, accompanied by a simultaneous improvement in hardness and scratch resistance. This study underscores laser gas nitriding as a potent strategy to augment the comprehensive surface characteristics of MGRs. This enhancement is poised to significantly extend their service life and reinforce their reliability when utilized as structural and functional materials in sectors such as machinery, national defense, and aerospace.

Dynamic mechanical properties and microstructure of ultrafine slag powder cement paste utilizing solid waste industrial tailings powder and fly ash

Ultrafine slag powder cement paste (USP-CP) is a promising green cementitious material with excellent mechanical properties and environmental benefits. In this study, the effects of elemental molar ratios in raw materials (n(Si)/n(Al) ranged from 1.2 to 1.4 with a gradient of 0.1; n(Fe)/n(Al) ranged from 0.15 to 0.21 with a gradient of 0.03; and n(S)/n(Al) ranged from 0.20 to 0.28 with a gradient of 0.04.) on the workability, mechanical properties, and microstructure of USP-CP were investigated. The main products of USP-CP are α-SiO2, AFt, gypsum, and α-C2SH. The molar ratio of Si/Al has the greatest influence on workability, while the molar ratio of S/Al has the greatest influence on setting time. For mechanical property tests, higher USP content can improve the early compressive strength of USP-CP, while its long-term compressive strength is affected by the anhydrous calcium sulfate (CaSO4) content. Specifically, when the molar ratios of Si/Al, Fe/Al, and S/Al are 1.2, 0.21, and 0.24, respectively, the 28-day dynamic and static compressive strengths of USP-CP specimens reach the maximum values, which are 121.3 MPa (321/s) and 42.0 MPa (10-2/s), respectively. Furthermore, the static compressive strength is comparable to that of pure cement of the same grade.The molar ratio of S/Al has a more significant effect on dynamic compressive strength than static compressive strength. The excessive increase of Na and Si elements in the alkaline activator inhibits the dynamic mechanical enhancement performance of USP-CP. This study provides theoretical and practical reference value for the application of USP in impact-resistant structural materials and static load-bearing materials. It also fully utilizes waste materials to reduce the use of cement and achieves environmental benefits of carbon reduction.

Influence of He injection amount on the microstructure of ion irradiated Cr0.8FeMnNi medium entropy alloy compared with 316L stainless steel

In recent years, medium and/or high-entropy alloys (M/HEAs) have attracted attention due to their excellent mechanical properties, positioning them as potential candidates for structural materials in advanced nuclear reactors. This study investigated the effect of He injection amount on the microstructural evolution in Cr0.8FeMnNi MEA and 316L stainless steel. Helium atoms were injected, followed by Fe2+ irradiation. Transmission electron microscopy was used to characterize the irradiation-induced defects. The primary irradiation-induced defects observed across all He injection amounts were black dots; no voids were seen under any irradiation conditions. In He-injected Cr0.8FeMnNi, the number density of black dots was significantly lower than in non-He-injected Cr0.8FeMnNi, while the average size of black dots increased with higher He injection rates. As the He injection amount increased, the binding energy of the self-interstitial atom (SIA) to the He-V complex decreased. This reduction facilitated the nucleation and growth of numerous SIA clusters within the matrix, consequently increasing the number density of black dots. The change in the number density of black dots in Cr0.8FeMnNi was much smaller than that observed in 316L. This could be ascribed to the enhanced self-healing process caused by the diversity of point defects and higher lattice distortion in Cr0.8FeMnNi.

Thermal stability of 3D interface Cu/Nb nanolaminates

Nanocrystalline alloys are promising structural materials yet lack thermal stability in many cases. Recent work shows that interface structure has an outsize effect on the thermal behavior of nanostructured alloys. This work focuses on the role of controlled heterophase interface structure in the thermal evolution of model Cu/Nb nanolaminates. We introduce 3D interfaces containing nanoscale heterogeneities in all spatial dimensions between Cu and Nb, forming 3D Cu/Nb. TEM, nanoindentation, and DSC are used in tandem to establish thermal stability and to identify shifts in microstructure as a function of static annealing temperature. 3D interfaces are shown to survive annealing to 300 °C for 1 hr., while 3D Cu/Nb microstructure evolves to form low-density and voided regions correlating to the onset of layer pinch-off between 500 and 600 °C annealing temperatures. A diffusivity- and vacancy energetics-based mechanism is developed to explain void formation driven by 3D interface degradation at elevated temperature.

Bayesian Conavigation: Dynamic Designing of the Material Digital Twins via Active Learning.

Scientific advancement is universally based on the dynamic interplay between theoretical insights, modeling, and experimental discoveries. However, this feedback loop is often slow, including delayed community interactions and the gradual integration of experimental data into theoretical frameworks. This challenge is particularly exacerbated in domains dealing with high-dimensional object spaces, such as molecules and complex microstructures. Hence, the integration of theory within automated and autonomous experimental setups, or theory in the loop-automated experiment, is emerging as a crucial objective for accelerating scientific research. The critical aspect is to use not only theory but also on-the-fly theory updates during the experiment. Here, we introduce a method for integrating theory into the loop through Bayesian conavigation of theoretical model space and experimentation. Our approach leverages the concurrent development of surrogate models for both simulation and experimental domains at the rates determined by latencies and costs of experiments and computation, alongside the adjustment of control parameters within theoretical models to minimize epistemic uncertainty over the experimental object spaces. This methodology facilitates the creation of digital twins of material structures, encompassing both the surrogate model of behavior that includes the correlative part and the theoretical model itself. While being demonstrated here within the context of functional responses in ferroelectric materials, our approach holds promise for broader applications, such as the exploration of optical properties in nanoclusters, microstructure-dependent properties in complex materials, and properties of molecular systems.

Ablation behavior and mechanisms of Cf/(CrZrHfNbTa)C‒SiC high‐entropy composite at temperatures up to 2450°C

AbstractThe oxide layer formed by ultra‐high melt point oxides (ZrO2, HfO2) and SiO2 glassy melt is the key to the application of traditional thermal structural materials in extremely high‐temperature environment. However, the negative effect of ZrO2 and HfO2 phase transitions on the stability of oxide layer and rapid volatilization of low viscosity SiO2 melt limit its application in aerospace. In this study, the ablation behavior of Cf/(CrZrHfNbTa)C‒SiC high‐entropy composite was explored systematically via an air plasma ablation test, under a heat flux of 5 MW/m2 at temperatures up to 2450°C. The composite presents an outstanding ablation resistance, with linear and mass ablation rates of 0.9 µm/s and 1.82 mg/s, respectively. This impressive ablation resistance is attributed to the highly stable oxide protective layer formed in situ on the ablation surface, which comprises a solid skeleton of (Zr, Hf)6(Nb, Ta)2O17 combined with spherical particles and SiO2 glassy melt. The irregular particles provide a solid skeleton in the oxides protective layer, which increased stability of the oxide layer. Moreover, the spherical particles have a crystal structure similar to that of Ta2O5 and are uniformly distributed in SiO2 glassy melt, which hinder the flow of SiO2 glassy melt and enhance its viscosity to a certain degree. And it reduces the volatilization of SiO2. In summary, the stable oxide layer was formed by irregular particles oxide and the SiO2 glassy melt with certain viscosity, thereby resulting in the impressive ablation resistance of the composite. This study fills a gap in ablation research on the (CrZrHfNbTa)C system.

Long-term relaxation analysis of steel cables based on viscoelastic model

Steel cables, renowned for their lightweight and high-strength properties, stand as ubiquitous building materials in large-span structures. Serving as crucial load-bearing elements, cables endure sustained tension throughout the structure's lifecycle. To further investigate the long-term relaxation characteristics of steel cables and provide more theoretical basis for structural relaxation calculations, this paper introduces a long-term relaxation constitutive model for steel cables, formulated through theoretical derivation, experimental validation, and data fitting techniques to establish time-dependent constitutive relationships. By employing the Bingham and Kelvin viscoelastic models, a relaxation model for steel cables is presented and optimized accordingly. Experimental investigations involve long-term tests on steel cables with three different sizes and detailed fitting analysis on collected internal force relaxation data. The findings emphasize the indispensability of structural relaxation behavior and the significance of altering internal forces, particularly in large-span cable-strut structures. The developed numerical model enables accurate simulation and prediction of long-term time-dependent performance in such structures, serving as a springboard for future studies in this domain.

Advanced cement composites: Investigating the role of graphene quantum dots in improving thermal and mechanical performance

The investigation of graphene quantum dots (GQDs) at very small nano- and atomic sizes is a novel approach in the fields of structural cement, concrete, and ceramic materials, which have not been thoroughly explored. This study investigates the comparative effects of two variations of GQDs, Qdl and Qdp, against a control mixture to assess the potential of graphene derivatives in enhancing thermal and mechanical properties of cement composites. The research presents their influences across a wide range of attributes, including flowability, bulk density, permeable voids, water absorption, compressive strength, flexural strength, surface temperature, thermal conductivity, thermal diffusivity, specific heat capacity, Brunauer-Emmett-Teller (BET) isotherm, thermogravimetric analysis (TGA), and microstructural characteristics. The empirical data underscore the superior freshness, physical, mechanical, and thermal attributes of GQDs-infused cement composites. Notably, the composites with 0.3 % Qdl show 20.8 % and 50 % increases in compressive and flexural strengths, respectively. On the other hand, the composites with 1.2 % Qdp show significant improvements in both compressive and flexural strengths, being 40 % and 108 % stronger than the control, respectively. Additionally, the thermal properties of the composites exhibit a proportional enhancement with increasing GQDs content. Microstructural analyses reveal a nano-bridging mechanism well-uniformly facilitated by the secondary nucleation and crystallization of calcium silicate hydrate (CSH) gel. This investigation offers innovative insights into the incorporation of GQDs in cement composites, highlighting their potential to create highly conductive structural cement and ceramic.

Using Poisson’s ratio and acoustic anisotropy parameter to assess damage and accumulated plastic strain during fatigue loading of austenitic steel

The work investigated the effect of fatigue failure on the elastic characteristics of metastable austenitic steel AISI 321: Poisson’s ratio and acoustic anisotropy parameter. The elastic characteristics were calculated using ultrasonic measurements of the propagation time of longitudinal and shear elastic waves. The volume fraction of strain-induced martensite was determined by the eddy current method. Theoretical studies have shown that the main factors influencing Poisson’s ratio are the accumulation of microdamages and changes in phase composition. The change in the acoustic anisotropy parameter is associated with the influence of cyclic deformation on the crystallographic texture of the material matrix and the formation of oriented crystals of strain-induced martensite. Based on the analysis of experimental results, expressions were obtained for calculating damage and relative accumulated plastic deformation based on acoustic measurement data, which are widely used in engineering practice to determine the fatigue life of structural materials.