High-performance Structural Materials Research Articles

Influence of interstitial carbon content on the microstructure, mechanical and electrochemical corrosion properties of CoFeNiMn multi-principal component alloys

In this study, the effects of carbon content on the microstructural evolution as well as compression and electrochemical corrosion properties of CoFeNiMn multi-principal component alloys (MPCAs) were investigated. A series of (Co25Fe25Ni25Mn25)100−xCx (x = 4, 5, 6, 7, 8) alloys were prepared by vacuum arc melting. Increasing carbon content, the structure transits from a single face-centered-cubic (FCC) phase into a mixed structure containing FCC phase and M23C6 carbides. The yield strength and hardness of the (Co25Fe25Ni25Mn25)100−xCx alloys were enhanced by increasing carbon content, which in turn decreases the ductility. The alloys containing eutectic carbides had a good combination of high yield strength (880 MPa), high fracture strength (2773 MPa), and large fracture strain (47%). Electrochemical measurements indicated that carbon content evidently affects the corrosion resistance of (Co25Fe25Ni25Mn25)100−xCx alloys in 3.5 wt% NaCl solution. Their corrosion resistance initially increases and then decreases with increasing carbon content. The increase in M23C6 carbides can accelerate pitting corrosion and degenerate their corrosion resistance. These findings not only provide comprehensive understanding of the carbon-alloyed behavior in FCC-type MPCAs but also show their potential engineering application as high-performance structural materials.

Revealing extraordinary work-hardening capacity in a high-entropy alloy with homogeneous composite structures

High performance structural metal materials with high strength and certain ductility have a wide range of critical applications in fields such as aviation, aerospace, transportation. A vein-shaped structure composed of recrystallized ultrafine grains was introduced into a nano-precipitated high-entropy alloy (HEA) by inter-critical annealing after cold rolling. The vein-shaped structure coupled with nanoprecipitates contributes a remarkable improvement of mechanical properties, with yield strength enhanced from 1232 MPa to 1510 MPa, ultimate tensile strength from 1544 MPa to 1745 MPa, and uniform elongation from 1.84 % to ∼7 %, compared to the as-rolled matrix. The synchronized increase in strength and ductility is the outcome of controlling multiscale strengthening mechanisms from tailoring dislocations, nanoprecipitates, bimodal grains, and deformation microbands, which activate the potential work-hardening capacity in the present HEA.

3D printed hierarchical interpenetrating phase composites with multi-scale mechanical energy absorption mechanisms

Lightweight, strong, and energy-absorbing materials are highly sought after in practical engineering applications. To this end, interpenetrating phase composites (IPC) stand as a novel class of composite materials to better leverage the properties of their constituents. Their structural design, however, has been limited to only specific structural features at a certain length scale in the existing studies. Inspired by the hierarchical composite materials in nature, this work proposes a novel concept of hierarchical interpenetrating phase composites (HIPC) by polymer infiltration into 3D printed hierarchical porous ceramic lattices. The hierarchical porous alumina lattices have up to three levels of porosity, including 3D printed macropores (≈300 μm), emulsion-templated micropores (≈10 μm), and sub-micropores (<1 μm) from partial sintering. Upon epoxy infiltration, three-level HIPC is constructed with hierarchically incorporated epoxy domains and alumina-epoxy interfaces, which leads to its unique multi-scale mechanical energy absorption mechanisms. Featuring a particularly porous and lightweight ceramic lattice, three-level HIPC exhibits an excellent combination of high specific compressive strength (64.6 kN m/kg), specific flexural strength (39.2 kN m/kg), and SEA (18.4 kJ/kg). In addition, even with a low ceramic content, three-level HIPC can effectively enhance the thermal conductivity via its hierarchically continuous ceramic microstructure. Therefore, our three-level HIPC has demonstrated impressive mechanical and thermal enhancement with its exquisite hierarchical architecture. The hierarchical structural engineering approach also represents a paradigm shift from constructing single-scale IPCs to multi-scale HIPCs and can be extended to other material combinations for high-performance structural and functional materials.

Symbiotically engineered crystalline-amorphous nanostructure in a strong-yet-stable Al alloy with large twinning-induced plasticity

High performance structural materials with combinations of excellent yet often mutually exclusive properties such as high yield strength, ductility and thermal stability are primarily accessed by synthesizing heterogeneous microstructures. Age-hardened Al alloys with hierarchical nanoprecipitates manifest a good combination of strength and ductility compared to fully amorphous Al alloys, however their thermal stability is in general low, stem from the fast-diffusion element-driven coarsening of nanoprecipitates at elevated temperature. Utilizing the sluggish-diffusion element Cr in the Al matrix, we propose a novel strategy of architecting symbiotically crystalline-amorphous nanostructure (CANS) endowed with self-assembled Cr segregation at crystalline/amorphous interfaces, to develop thermally stable, ultrastrong and ductile Al alloys. The symbiotic CANS-AlCr alloys with homogeneous twinning-induced plasticity of ∼15% strains at room temperature have ultrahigh compressive yield strength of ∼1.75 GPa and outstanding thermal stability up to ∼623 K, simultaneously superior to the parent nanocrystalline and amorphous Al alloys. The interfacial Cr segregation not only promotes twinning-induced plasticity of crystals but also triggers dynamic elemental partitioning between interfaces and amorphous nanolayers, which is critical to their thermodynamic and mechanical stabilization of symbiotic CANS-AlCr alloys. Our strategy advances efficient creation of hierarchical nanostructure and offers a facile route that is regulated across atomic and nanoscopic scales to achieve desirable materials with diverse-yet-precise performances.

First principles prediction of yield strength of body centered cubic structured high entropy alloys

High entropy alloys (HEAs) with a body centered cubic (bcc) crystal structure have emerged as potential high-performance structural materials due to their high strength at room and elevated temperatures. In this study, a computational approach, based on the revised Peierls-Nabarro model and using the inputs solely calculated from the first principles density functional theory, has been developed to predict the yield strength of bcc HEAs. Examining its accuracy and reliability, the developed computational approach was applied to four different types of bcc HEAs. The yield strength was predicted to be 1034 MPa for MoNbTaW, 1489 MPa for MoNbTaV, 1356 MPa for AlCoCrFeNi, and 1740 MPa for AlCoCrFeNiZr0.3 alloy, respectively. These computational predictions are found to agree well with available experimental data. Moreover, the developed computational approach accurately quantifies the changes in the yield strength from MoNbTaW to MoNbTaV with a change of constituent W to V, and from AlCoCrFeNi to AlCoCrFeNiZr0.3 with addition of 6 at% Zr. Therefore, this first-principles based computational approach provides a way for expedite optimization on the mechanical properties of bcc HEAs across vast composition space.

Combining laminated bimodal heterostructure and dislocation source limitation for superior strength-ductility synergy

Many unremitting pursuits have been paid on designing microstructures to enhance the strength-ductility synergy of metallic materials. In this work, laminated bimodal heterostructure and dislocation source limitation were introduced together into pure Ni with various laminate thicknesses by electrodeposition and subsequent annealing to circumvent the limitations of the strength-ductility trade-off. The specimen, composed of alternative fine-grained and ultrafine-grained laminates with the optimized laminate thickness, had a combination of 601 MPa yield strength which was 4.8 times its Hall-Petch yield strength (124 MPa), and 24.5% reasonable ductility. The combination went beyond the range established by the reported pure Ni. When the fine-grained laminates started dislocation slip first and ultrafine-grained ones remained elastic, incompatible deformation between the two different laminates resulted in a high density of piled-up geometrically necessary dislocations (GNDs) against the interfaces, increasing the yield strength. Deformation incompatibility was also present in each of the individual laminates exhibiting bimodal structure, which further facilitated strengthening and strain hardening. Plentiful dislocation cells and walls were found to form inside the fine-grained laminates during work hardening, which could contribute to the production of GNDs. The carefully constructed heterostructures maximized the role of GNDs. Besides, dislocation source limitation induced further hardening, in the form of the yield-point behaviour, and ductilization which resulted from more room inside grains for the accumulation and interaction of dislocations. The superior strength-ductility synergy here paves a promising paradigm for designing high-performance structural metallic materials.

Microstructural evolution and mechanical properties of (FeCoNi)85·84Al7·07Ti7.09 high-entropy alloy by selective laser melting with aging treatment

Faced-centred cubic nanoparticles-strengthened FeCoNiAlTi system high-entropy alloy (HEA) has demonstrated unique mechanical performance advantages with recently developed HEA alloy compositions. One of the key factors determining the performance of an alloy is the efficient manipulation of precipitation. However, the traditional aging method used to achieve this can be problematic. It is time-consuming and difficult to accurately control the distribution of the precipitated phase, which restricts the development of new, high-performance structural materials. Consequently, researchers have been exploring alternative methods to more precisely and effectively manipulate precipitation in alloys. Here, we have utilized both high-efficiency additive manufacturing processes and a short-term aging process to produce (FeCoNi)85·84Al7·07Ti7.09 high-entropy alloys that exhibit outstanding mechanical properties with an ultimate tensile strength of 1625 MPa, yield strength of 1214 MPa and an elongation to failure of 11.6%. Our findings reveal the formation of L12 and L21 nanoparticles phases after aging treatment, and their contents gradually decrease with increasing aging treatment temperature. And, we introduce two strengthening mechanisms of dislocation strengthening and precipitation strengthening into the alloys, and realized the coexistence of high-density dislocations and precipitated phases, thereby exhibiting excellent comprehensive mechanical properties. This approach represents a promising new direction in the development of high-performance alloys, offering a more efficient and effective means of producing materials with improved properties.

All-natural and high-performance structural material based on lignin-reinforced cellulose

Sustainable materials derived from lignocellulosic resources are attractive alternatives to ubiquitous petrochemical plastics. However, it remains a huge challenge to improve the mechanical properties of lignocellulosic materials through efficient and low-energy processing strategy. Herein, we report a facile lignin-reinforced cellulose strategy to manufacture an all-natural and high-performance structural material from bamboo particles via partial delignification followed by hot-pressing. Partial delignification can regulate the amount of lignin in the bamboo particles and release internal cellulose microfibers. The subsequent hot-pressing drives residual lignin into the cellulose matrix to form a dense structure, which acts as a polyphenolic binder to improve the performance of the structural material. The obtained lignin-reinforced cellulose plate (LRCP) demonstrates high isotropic flexural strength (∼162 MPa), which is higher than that of natural bamboo and typical petrochemical plastics. Moreover, LRCP shows outstanding toughness (∼2.58 MPa m1/2), excellent compressive strength (∼178 MPa), improved wet stability and superior flame resistance. LRCP is all-natural and eco-friendly without the need for additional chemical cross-linking reagents. We believe that this facile and cost-effective strategy provides a promising way to process lignocellulosic resources into all-natural and high-performance structural materials that can serve as powerful plastic alternatives in the future.

Automated trackspinning of aligned lignin fibers as precursors of green carbon nanofibers

At present, most carbon fibers are made from non-renewable polyacrylonitrile. Substantial efforts have been made to replace petroleum-based precursors for carbon fiber production. Interestingly, lignin is a carbon fiber precursor material that is cheap, highly available and sustainable. Submicron-scale lignin-based carbon nanofibers are used in numerous areas, such as electronic devices, batteries, supercapacitors and low-cost, high-performance structural composite materials. Trackspinning (TS) technology offers a way to scale up the versatile, but inefficient contact drawing technique to produce small-diameter lignin fibers from environmentally friendly aqueous solutions. In this study, the effects of TS based on probe drawing of low-concentration lignin nanofibers blended with poly(ethylene oxide) and glycerol in sodium hydroxide (NaOH) solution were investigated. The TS lignin fibers were well aligned and reached diameters as small as 500–1000 nm as the drawing length was increased. Lignin fiber macromolecular alignment was isotropic at low levels of draw, and the dichroic ratio increased from 1 to 2.25 with doubling of the drawing length. The most highly drawn trackspun lignin fibers had a mechanical strength of 3.92 MPa and a Young’s modulus of 2.15 GPa, which were similar to reported values for solvent-electrospun lignin nanofibers. These findings support the potential to utilize TS to produce small-diameter lignin fibers using a simple aqueous solvent approach.

Enhancing mechanical properties and improving mechanical anisotropy of rolled 2024 Al sheet by TiB2 nanoparticles

Aluminum alloys with high mechanical properties and alleviated mechanical anisotropy are required for engineering applications. Traditional aluminum alloy sheets processed by rolling usually have a higher strength but a lower ductility, leading to a strength-ductility trade-off. Moreover, the rolling deformation could lead to obvious mechanical anisotropy. In this study, we report that the introduction of in-situ TiB2 nanoparticles can enhance the strength and ductility simultaneously of aluminum alloy in terms of rolled 2024 Al, which thus can overcome the strength-ductility trade-off dilemma faced by traditional aluminum alloy sheets. Moreover, the mechanical anisotropy of rolled 2024 Al can be alleviated significantly. The influencing mechanisms of TiB2 nanoparticles on strength-ductility and mechanical anisotropy are discussed in detail. The TiB2 particles enhance the strength of 2024 alloy mainly through grain boundary strengthening, Orowan strengthening, and load-bearing strengthening, and meanwhile enhance ductility through decreasing the dynamic recovery rate of dislocation. The mechanical anisotropy is alleviated by the elongated-to-equiaxed transition on grain structure and the weak texture. This study provides a new insight into the design of high-performance structural materials with alleviated mechanical anisotropy.

Carbon fiber from Biomass sources: A Comprehensive Review

Global energy demand is rising, fossil fuel prices are rising, fossil fuel reserves are running out, and fossil fuel use contributes to the greenhouse effect. As a clean alternative source of energy to fossil fuels, biomass is becoming more and more essential. Carbon fiber (CF), often known as graphite fiber, is a thin, strong, and adaptable material utilized in both structural (capacity) and non-structural applications (e.g., thermal insulation).Precursors are the raw materials used to create carbon fiber, which is mostly derived from fossil fuels. Because of the high cost of precursors and manufacture, carbon fiber has only found employment in a few numbers of high-performance structural materials (e.g., aerospace). To reduce the price of CF and reliance on fossil fuels, numerous alternative precursors have been studied throughout the years, including biomass-derived precursors including rayon, lignin, glycerol, and lignocellulosic polysaccharides. This study's goal is to present a detailed study of biomass-derived CF precursors and their market potential. We look into the viability of producing CF from these precursors, as well as the state of technology, potential applications, and cost of production (when data are available). We go over their benefits and drawbacks. We also talk about the physical characteristics of CF made from biomass and contrast them with CF made from polyacrylonitrile (PAN). Additionally, we go into bio-based CF manufacturing and end-product concerns, logistics for biomass feedstock and plant sites, feedstock competition, and risk-reduction techniques. This paper offers a comprehensive overview of the CF potential from all biomass sources and can be used as a resource by both novice and seasoned professionals who are interested in producing CF from non-traditional sources.

A novel metal-ceramic composite combining the structures of nacre and nanofiber reinforced foam

Lightweight high-strength and tough composites have enormous potentials in a multitude of fields including biomaterials, sporting goods, aerospace and automobile industries. Herein, we present a strategy to develop a novel bulk Al/SiC composite with a nacre/foam hybrid structure to combine excellent lightweight of foams with outstanding strength and toughness of nacre. To reduce the adverse effect of foam pores on mechanical properties, we further propose to strengthen the foams with 3D nanofiber networks, obtaining a nacre/nanofiber reinforced foam structure. Simultaneously, new particle-bubble co-assembly and selective infiltration technologies are proposed to prepare the novel nacre/foam and nacre/nanofiber reinforced foam structures. The nacre/nanofiber reinforced foam composite shows greater specific strength and toughness than the nacre/foam composite, conventional dense Al/SiC composites and many engineering materials. Our approach opens a promising new avenue for the structure design and manufacturing of lightweight, high-performance structural materials.

Constructing An All-Natural Bulk Structural Material from Surface-Charged Bamboo Cellulose Fibers with Enhanced Mechanical and Thermal Properties.

Bamboo is widely distributed, rapidly regenerable, and incorporates long cellulose fibers, which make it one of the most lightweight and strong natural materials. Processing bamboo into a high-performance structural material for plastic replacement is highly promising but challenging. In this study, an all-natural, high-performance structural material is derived from natural bamboo with superior mechanical and thermal properties that benefit from the introduction of surface charge and further layer-by-layer assembly of bamboo cellulose fibers. The obtained modified bamboo fiber plate (MBFP) transcends the constraints of the natural size and anisotropy of bamboo, showing high flexural strength (ca. 179 MPa) and flexural modulus (ca. 12 GPa). Moreover, the product has an extremely low coefficient of thermal expansion (ca. 11.3×10-6 K-1 ), high thermal stability, and superior fire resistance. The excellent mechanical and thermal properties combined with the efficient and rational manufacturing process make MBFP a powerful plastic alternative for furniture, construction, and automotive industries.

Robust flexural performance and fracture behavior of TiO2 decorated densified bamboo as sustainable structural materials

High-performance, fast-growing natural materials with sustainable and functional features currently arouse significant attention. Here, facile processing, involving delignification, in situ hydrothermal synthesis of TiO2 and pressure densification, is employed to transform natural bamboo into a high-performance structural material. The resulting TiO2-decorated densified bamboo exhibits high flexural strength and elastic stiffness, with both properties more than double that of natural bamboo. Real-time acoustic emission reveals the key role of the TiO2 nanoparticles in enhancing the flexural properties. The introduction of nanoscale TiO2 is found to markedly increase the degree of oxidation and the formation of hydrogen bonds in bamboo materials, leading to extensive interfacial failure between the microfibers, a micro-fibrillation process that results in substantial energy consumption and high fracture resistance. This work furthers the strategy of the synthetic reinforcement of fast-growing natural materials, which could lead to the expanded applications of sustainable materials for high-performance structural applications.

Microstructural Characteristics of High-Pressure Die Casting with High Strength-Ductility Synergy Properties: A Review.

In response to the increased emphasis on reducing carbon emissions, the demand for lightweight, high-performance structural materials is quickly increasing, and Mg alloys, because of their having the lowest density among the common engineering metals, have demonstrated considerable advantages and prospective applications in contemporary industry. High-pressure die casting (HPDC), owning to its high efficiency and low production cost, is the most extensively utilized technique in commercial Mg alloy applications. The high room-temperature strength-ductility of HPDC Mg alloys plays an important role in their safe use, particularly in the automotive and aerospace industries. With respect to HPDC Mg alloys, their mechanical properties highly rely on their microstructural characteristics, particularly the intermetallic phases, which are further dependent on the alloys' chemical compositions. Therefore, the further alloying of traditional HPDC Mg alloys, such as Mg-Al, Mg-RE, and Mg-Zn-Al systems, is the most adopted method to further improve their mechanical properties. Different alloying elements lead to different intermetallic phases, morphologies, and crystal structures, which can have helpful or harmful effects on an alloy's strength or ductility. The methods aimed at regulating and controlling the strength-ductility synergy of HPDC Mg alloys have to arise from an in-depth understanding of the relationship between the strength-ductility and the components of the intermetallic phases of various HPDC Mg alloys. This paper focuses on the microstructural characteristics, mainly the intermetallic phases (i.e., components and morphologies), of various HPDC Mg alloys with good strength-ductility synergy, aimed at providing insight into the design of high-performance HPDC Mg alloys.

A novel cobalt-free oxide dispersion strengthened medium-entropy alloy with outstanding mechanical properties and irradiation resistance

A novel cobalt-free oxide dispersion strengthened (ODS) equiatomic FeCrNi medium entropy alloy (MEA) was successfully fabricated through mechanical alloying and hot extrusion (HE). The ODS FeCrNi MEA is composed of a single face-centered cubic (FCC) matrix, in which highly dispersed oxide nanoparticles, including Y2Ti2O7, Y2TiO5 and Y2O3, are uniformly distributed. Compared with the FeCrNi MEA, the ODS FeCrNi MEA exhibits the improved yield strength (1120 MPa) and ultimate tensile strength (1274 MPa) with adequate ductility retention (12.1%). Theoretical analysis of the strengthening mechanism indicates that the high strength is mainly attributed to the grain-boundary strengthening caused by fine grains and the precipitation strengthening resulted from the oxide nanoparticles. Meanwhile, the matrix that easily activates mechanical twinning during the deformation process is the main reason to ensure moderate ductility. In addition, the introduction of high-density oxide nanoparticles can disperse the defect distribution and suppress the defect growth and irradiation-induced segregation, leading to the excellent irradiation resistance. These findings provide innovative guidance for the development of high-performance structural materials for future nuclear energy applications with balanced strength and ductility.

Ultra-lightweight living structural material for enhanced stiffness and environmental sensing.

Natural materials such as bone, wood, and bamboo can inspire the fabrication of stiff, lightweight structural materials. Biofilms are one of the most dominant forms of life in nature. However, little is known about their physical properties as a structural material. Here we report an Escherichia coli biofilm having a Young's modulus close to 10​GPa with ultra-low density, indicating a high-performance structural material. The mechanical and structural characterization of the biofilm and its components illuminates its adaptable bottom-up design, consisting of lightweight microscale cells covered by a dense network of amyloid nanofibrils on the surface. We engineered E.coli such that 1) carbon nanotubes assembled on the biofilm, enhancing its stiffness to over 30​GPa, or that 2) the biofilm sensitively detected heavy metal as an example of an environmental toxin. These demonstrations offer new opportunities for developing responsive living structural materials to serve many real-world applications.

Microstructure and mechanical properties of Al-Fe-Co-Cr-Ni high entropy alloy fabricated via powder extrusion

A novel non-equiatomic Al15.85Fe11.15Co32.11Cr10.76Ni30.13 high entropy alloy (HEA) was fabricated via powder metallurgy (P/M) method. The Al15.85Fe11.15Co32.11Cr10.76Ni30.13 HEA exhibits dual-phase microstructure consisting of face-centered-cubic (FCC) and body-center cubic (BCC) phases. The Al15.85Fe11.15Co32.11Cr10.76Ni30.13 HEA has high compressive yield strength of 938 MPa and fracture strength of 3360 MPa, and still maintains moderate fracture strain higher than 40%. Also, the Al15.85Fe11.15Co32.11Cr10.76Ni30.13 HEA has high strength of 518 MPa at the temperature of 600 °C. Microstructural characterization shows that a large number of L12 and B2 nanoprecipitates are uniformly dispersed in the FCC and BCC phases, respectively, contributing to the enhancement of the strength of the two phases. The effective combination of FCC and BCC phases eventually leads to the high strength of the Al15.85Fe11.15Co32.11Cr10.76Ni30.13 HEA. This finding provides novel guidance for the development of high-performance structural materials with superior balance of strength and ductility for future industrial applications.

A unified non-empirical strength model

Strength, as an important indicator of structural materials, has always been an important research topic in materials science. Theoretically, building a strength model is a rewarding method to understand the relationship between the mechanical properties and microstructure of materials. Although many strength models can reduplicate experimental values very well, they are empirical models, and their applicability is limited to materials for which empirical parameters have been obtained. Here, a non-empirical strength model is proposed based on the two-dimensional (2D) displacement potential of dislocation slipping, which can be applied to different chemically bonded crystals. Owing to the large electron localization function (ELF), covalent and ionic crystals have a high 2D displacement potential of dislocation slipping, and their dislocation slip mode prefers the kink-pair mode, further exhibiting a high critical resolved shear stress (CRSS). In contrast, metallic crystals with a small ELF have a low 2D displacement potential of dislocation slipping, and their dislocation slip mode is more inclined to the string mode, showing a low CRSS. This work provides new insights into dislocation-slipping configurations that will be useful for the development of new high-performance structural materials.

Relating plasticity to dislocation properties by data analysis: scaling vs. machine learning approaches

Plasticity modelling has long relied on phenomenological models based on ad-hoc assumption of constitutive relations, which are then fitted to limited data. Other work is based on the consideration of physical mechanisms which seek to establish a physical foundation of the observed plastic deformation behavior through identification of isolated defect processes (’mechanisms’) which are observed either experimentally or in simulations and then serve to formulate so-called physically based models. Neither of these approaches is adequate to capture the complexity of plastic deformation which belongs into the realm of emergent collective phenomena, and to understand the complex interplay of multiple deformation pathways which is at the core of modern high performance structural materials. Data based approaches offer alternative pathways towards plasticity modelling whose strengths and limitations we explore here for a simple example, namely the interplay between rate and dislocation density dependent strengthening mechanisms in fcc metals.