Multilevel Microstructure Research Articles

Atomic Insight into Multilevel Microstructure Evolution and Energy Variation Mechanisms of Polyimide under Shock Compression

Atomic Insight into Multilevel Microstructure Evolution and Energy Variation Mechanisms of Polyimide under Shock Compression

Insight into austenite reversion and mechanical behavior of quenching and partitioning steel inherited hierarchical structure of martensite

In this paper, the start microstructure of full martensite and dual phases comprising ferrite and martensite were introduced into quenching and partitioning (Q&P) steel to tailor the microstructural characteristics and mechanical behaviors, which was achieved by means of a pre-quenching treatment with various temperatures. It is revealed that the conventional Q&P sample possessed bimodal microstructure with predominantly blocky feature, while gradually changed from combination of blocky and lath structures into individually lath feature in pre-quenched Q&P samples. The reversed austenite presented different variants, which predominantly reproduced the orientation of parent austenite and occasionally possessed twin relationship, low angle misorientation or extraneous with parent austenite. The twin-related austenite included annealing twin and reversed twin, whilst the latter showed twin relationship with both neighbored annealing twin and parent austenite. The variant type of reversed austenite significantly influenced the characteristics of its orientation relationship with neighbored pre-quenched martensite. The pre-quenching treatment was favorable to improve the carbon content of meta-stable austenite before Q&P treatment, while the final carbon content in retained austenite was mainly controlled by the synergistic carbon partitioning of martensite and bainite on basis of thermodynamic calculation, accompanied with the partitioning of Mn and Si elements. Moreover, the pre-quenched martensite deformed coordinately in a unit of martensite packet and was beneficial to retard necking to improve ductility. The optimal mechanical properties were obtained with pre-quenching temperature near Ac3, possessing yielding strength of 623 MPa, ultimate tensile strength of 861 MPa and product of strength and elongation exceeding 28 GPa%, attributing to the positive TRIP effect originating from lath-like retained austenite with high carbon content and multi-level hierarchical microstructure inherited from pre-quenched martensite.

Effect of multistage lamellar microstructure on mechanical properties of Tc18 alloy

In this study, a three-step heat treatment approach, which included annealing, solution treatment at 740–820 °C, and aging at 450–550 °C, was employed to control the precipitation behavior of the α phase in TC18(Ti-5Al-5Mo-5 V-1Cr-1Fe) alloy. The multistage microstructure resulting was found to contain both the primary lamellar structure (α) and the secondary lamellar structure (αs), and the relationship between the spacing of multi-level lamellar microstructure and the mechanical properties of the alloy was effeciently determined. The study demonstrates that lowering the solid solution temperature reduces the interlayer spacing of the primary α phase, and increasing the aging temperature enlarges the interlayer spacing of the secondary αs phase, thereby enhancing the material's mechanical performance. Nevertheless, a substantial discrepancy in yield strength exists between these two interlayer spacings, which impacts the stress-strain coordination and reduces the plastic zone at the crack tip, and also increases the likelihood of formation of microvoids and microcracks at grain boundaries.

Studying the Incorporation of Multi-Walled Carbon Nanotubes in High-Performance Concrete

The current work aimed to study nanomodified HPC with multi-walled carbon nanotubes (MWCNT). The effect of MWCNT concentration, from 0% to 0.6% of cement weight, was evaluated on HPC multi-level output properties, namely, the flowability, mechanical strength, electrical resistivity, and microstructure. In addition, a tentative, simplified, and more cost-effective method based on dispersion of a high-pH solution of hydroxide was also adapted to disperse the MWCNT before incorporation in fresh HPC mixtures. Adding 0.2–0.6% MWCNT reduced HPC workability even with a higher superplasticiser dosage. The electrical resistivity was 484.58 Ω m for the HPC without MWCNT at 28 days of curing, while the samples with 0.2%, 0.4%, and 0.6% MWCNT presented 341.41 Ω m, 363.44 Ω m, and 360.34 Ω m, respectively. The use of 0.2–0.6% MWCNT in HPC decreased the flexural and compressive strength by 20% and 30%, respectively. The HPC performance decrease with MWCNT seemed to be related to relatively significant agglomerations of the long MWCNTs, namely, in HPC-0.6% samples. New developments are needed to state a simple and cost-effective dispersion method for MWCNT incorporation in HPC. In addition, smaller dosages of MWCNT are suggested for future research works.

Microstructure evolution and mechanical properties strengthening in laser powder bed fusion of high-strength SiC and TiB2 co-reinforced Al-Zn-Mg-Cu composites

A SiC and TiB2 particles reinforced Al-Zn-Mg-Cu matrix composite was designed and fabricated using laser powder bed fusion (LPBF). This study investigated the effects of ceramic reinforcements on the phase composition, microstructures, grain crystallization, and mechanical properties. The mechanisms of microstructure evolution and mechanical strengthening were discussed. Results show that a multi-level microstructure with ceramic reinforcements and nanoprecipitates has been developed. The ceramic reinforcements exhibited a uniform distribution within the matrix, while the eutectic precipitates formed a network substructure along the grain boundaries. A novel interfacial bonding mechanism, SiC/Al4C3 +eutectics/Al, has been developed through an in-situ reaction between SiC and Al. Ceramic reinforcements provided sufficient nucleation sites for grain nucleation, transforming from coarse columnar growing along the [001] direction parallel to the printing direction to fined equiaxed grains with random growth. The mechanical properties were enhanced, and the microhardness heterogeneity along different directions was reduced. The ultimate tensile strength and elongation were 516 ± 12 MPa and 6.12 ± 0.36%, respectively. The enhancement of mechanical properties was attributed to superior interfacial bonding strength, fine grain strengthening, solution strengthening, second phase strengthening, and substructural strengthening. This work could demonstrate the potential for fabricating AMCs using LPBF with Al-Zn-Mg-Cu alloy as the matrix.

Recrystallization effect on surface passivation of Hastelloy X alloy fabricated by laser powder bed fusion

Post-heat treatment is generally adopted in the additive manufacturing field due to its alleviation of high residual stress and modification of rapid-solidified multilevel heterogeneous microstructure, and the related performance of the heat-treated counterparts calls for a systemic investigation to build a criterion of the heat treatment procedure. In this work, we focus on the heat treatment effects on the recrystallization of the Hastelloy X alloy produced by the laser powder bed fusion (LPBF) method, and the related surface passivation of the heat-treated counterparts is meticulously assessed as well. Results show that the multilevel heterostructure for LPBF Hastelloy X alloy consists of sub-micro dislocation cell substructures with Cr/Mo elemental segregation, fine columnar grains, and periodically-distributed molten pools. After heat treatment, partially and fully recrystallized structures for LPBF Hastelloy X alloys were achieved at 1100 and 1200 °C for 1 h, respectively. Furthermore, the as-built LPBF Hastelloy X alloy shows superior corrosion resistance while the heat-treated one (1100 °C) exhibits the worst in the borate buffer solution. The growth of passive film exhibited a highly linear correlation with the nucleation process controlled by diffusion, and high dislocation density and low angle grain boundary decreased the diffusion coefficient of cation vacancies, augmenting the nucleation sites of the passive film and enhancing its growth rate. Moreover, the micro-galvanic effect resulting from the partially recrystallized microstructure actively facilitated the formation of inhomogeneous porous passive films, leading to the worst corrosion resistance.

Microstructure and properties of TiC/Fe24Ni24Co24Mn18 high-entropy composite with exceptionally low coercivity

It is challenging to achieve good combinations of excellent mechanical properties and low coercivity (≤200 A/m) in typical soft magnetic alloys. In this work, TiC/Fe24Ni24Co24Mn18 high-entropy composite (HEC) prepared by mechanical alloying (MA) and spark plasma sintering (SPS) was produced to achieve good combinations of strength-ductility synergy and low coercivity. After MA, the TiC/Fe24Ni24Co24Mn18 HEC powders were composed of a main face-centered cubic (fcc) phase and some body-centered cubic (bcc) phase. Following SPS, the bulk TiC/Fe24Ni24Co24Mn18 HEC consisted of a fcc phase with nanosized TiC. In detail, the HEC showed multilevel heterogeneous microstructure, i.e., ultra-fine fcc grains (∼0.38 µm), micron-sized fcc grains (∼1.49 µm), and uniform dispersion of the in-situ formed TiC nanoparticles (∼98 nm) in ultra-fine fcc grains. The bulk TiC/Fe24Ni24Co24Mn18 HEC exhibits a high tensile yield strength of ∼1167 MPa and an exceptionally low coercivity of ∼100.5 A/m, suggesting an outstanding combinations of mechanical and magnetic properties. Compared with previously reported Fe-Co alloys or high entropy alloys (HEAs), the TiC/Fe24Ni24Co24Mn18 HEC shows a significantly enhanced yield strength while maintaining a relatively low coercivity, primarily resulting from the heterogeneous microstructure caused by the in-situ formed TiC.

Influence of notch root radius on high cycle fatigue properties and fatigue crack initiation behavior of Ti-55531 alloy with a multilevel lamellar microstructure

Notch high cycle fatigue (HCF) properties and microcrack initiation behavior of Ti-55531 alloy with a multilevel lamellar microstructure under various notch radii were systematically investigated. Results indicate that the reduction of notch root radius significantly promotes fatigue microcrack initiation, and then dramatically reduces the HCF life and strength of the alloy. Cyclic deformation of the alloy is mainly controlled by the slipping and deformation twinning in α plates. The primary fatigue crack initiation micro-mechanism is α/β interface cracking induced by slipping and twinning at all notch HCF specimens. Moreover, the volume fraction of twinning would increase with decreasing of the notch root radius. Interestingly, when the notch root radius is the smallest (R = 0.14 mm) and the stress concentration factor is the largest (Kt = 4), in addition to slipping and twinning, basal stacking faults promoting the cracking of α/β interface could be another crucial HCF microcrack initiation mechanism of the alloy. Furthermore, with decreasing of notch root radius and increasing of stress concentration factor, the size of cycle plastic deformation zone at notch root gradually reduces to the size of α colony and even the α plate. Therefore, the order of influential degree of three different levels microstructure on the crack initiation mechanism of notched HCF can be arranged as α plate > α colony > β GB.

Thixotropic deformation behavior, rapid spheroidization and solid-liquid homogenization of semi-solid Al0.8Co0.5Cr1.5CuFeNi HEA with multilevel microstructure

In this paper, powder metallurgy-rapid heating and isothermal-holding (PMRHI) method was proposed to realize the rapid spheroidization and suppression of solid grain coarsening in semi-solid Al0.8Co1.5Cr0.5CuFeNi HEA. The thixotropic behavior and microstructure after PMRHI were investigated. Shear thinning effect exists during thixotropic deformation. The bimodal characteristics of flow stress degenerates with the proceeding of solid grain sliding (SS) and flow of liquid incorporating solid grains (FLS), indicating solid-liquid homogeneity and stable thixotropic deformation. The solid-liquid distribution homogeneity can suppress voids and hot tearing caused by liquid film channels. In multilevel semi-solid microstructure, the orientation relationship between solidified liquid phase and solid grain is approximately Kurdjumov-Sachs relationship, fine Al-Ni and Fe-Cr rich spinodal plates and nano Cu precipitates are formed in solid grain. The rapid spheroidization is realized due to initial dispersed powder metallurgy microstructure. After the steady thixotropic deformation of 1225 °C /0.05 s−1, mechanical properties were significantly improved.

Effect of annealing temperature on mechanical properties of TC21 titanium alloy with multilevel lamellar microstructure

The purpose of the present work is to reveal the effect of annealing temperature on the microstructure and mechanical properties of multilevel lamellar microstructure of TC21 titanium alloy in triple heat treatments, where the annealing temperatures are 760, 800 and 840 °C, respectively. The multilevel microstructure consists of β grain, α colony (αc), α plates (αp) and aged α plates (αs). The strength, plasticity, impact toughness and fracture toughness of the material were tested. The microstructure was characterized by using optical microscopy (OM), scanning electron microscopy (SEM), laser scanning confocal microscope (LSCM) and electron backscatter diffraction (EBSD). Results show that the size of αc increases and the widths of αp and βt increase gradually with the increase in annealing temperature. The number of αs precipitated on β matrix increases sharply and their size becomes smaller after aging treatment. The strength of TC21 titanium alloy increases as increasing annealing temperature while plasticity decreases. The αs is a critical unit which plays an important role in controlling strength of the alloy through Hall-Petch fitting. Furthermore, increasing the size of αc and decreasing the size of αp and αs are beneficial to increase the strength of the alloy. The impact toughness and fracture toughness of the alloy increase firstly then decrease with the increase in annealing temperature. The synergistic effect originating from different level α phase determine the toughness of the alloy. Massive cleavage and intergranular fractures in the fracture contribute to the increased length of crack propagation path so as to the decrease of toughness of the alloy. Meanwhile, it is confirmed found the toughness is also related to the change of size of αc after annealing treatment. And too large or too small size of αc is not conducive to the improvement of the toughness of the alloy.

Multilevel microstructure control of cast Al–7.0Si–4.0Cu alloy with high strength–toughness synergy via micro-alloying combined with manipulation by in-situ nano-ceramics

Incident Ti–Si poisoning when applying traditional agents of microstructure manipulation in Al–Si alloys is always adverse to realize multilevel microstructure control. This work combined the manipulation by physically formed in-situ nano-ceramics from Fe79.58B11.26Si9.26 amorphous alloy and the micro-alloying to comprehensively improve the microstructure configuration of Al–7.0Si–4.0Cu alloy. It was suggested that micro-alloying of Mg and Sb prominently refined α-Al dendrites and eutectic silicon. Micro-alloying with Mg increased the nucleating temperature of α-Al, meanwhile Mg atoms can hinder the growth of α-Al and eutectic silicon. Sb atoms can also be adsorbed to the growth interfaces of eutectic silicon hindering the growth process. On this basis, trace Fe79.58B11.26Si9.26 amorphous alloy brought further optimization on α-Al dendrites and eutectic silicon, especially Al2Cu and Mg2Si, realizing the multilevel microstructure control. In-situ Fe2B and Fe3Si nano-ceramics were confirmed to have low lattice misfits with α-Al and silicon, serving as efficient nucleation sites and growth retardants. After combined micro-alloying and manipulation, the mean sizes of α-Al and eutectic silicon were significantly refined by 72.7% and 79.9%, respectively, meanwhile, the ultimate tensile strength (UTS) and plastic strain (δ) were improved to 480 MPa and 9.4%, corresponding to 30.1% and 77.4% improvement, respectively. This work provides new mentality to realize multilevel microstructure control and improvement of strength–toughness synergy in Al–Si alloys.

Dynamic multi-level microstructured antifouling surfaces by combining quaternary ammonium modified GO with self-polishing copolymers

Marine biological fouling is the undesirable accumulation on the surfaces of submerged objects and causes environmental and economic consequence to ships and marine facilities. However, traditional coatings achieve antifouling by releasing toxic heavy metal antifouling agents, causing ecological problems. And the static antifouling performance of self-polishing antifouling coating is not good. To overcome the shortcoming, a novel antifouling strategy to build a self-renewing multi-level microstructure on the coating surface was developed by dispersing GO-based quaternary polymer brushes in a self-polishing fluoro/silyl acrylate copolymer. Quaternized GO exhibits excellent dispersibility in the silyl-based acrylate copolymer. A dynamic self-renewing surface is realized for the coating via a self-polishing effect that exposes the filler inside the coating at the surface. The multi-level microstructure of the sharp edge of GO and quaternized “spear” structure destroys the cell wall of organisms. And a “water-shield” on amphoteric ion surface on quaternized GO inhibits adhesion of organisms. The antibacterial and anti-algae tests demonstrated the excellent antifouling effect of the coating at only 0.1% (mass) filler content, with anti-algae ratio against Nitzschia closterium (N. closterium), Phaeodactylum tricornutum (P. tricornutum) and Halamphora sp. of 83.7%, 52.4%, and 65.8%, respectively. The proposed preparation method is simple and potentially applicable to large-scale production for antifouling application.

Membrane-Fresnel Diffractive Lenses with High-Optical Quality and High-Thermal Stability.

The membrane–Fresnel diffractive lens (M-FDL) has great potential in the field of high-resolution and lightweight imaging in orbit. However, the M-FDL with high-optical quality and high-thermal stability cannot be fabricated to a standard by the existing processing methods. In this paper, we propose a method for fabricating an M-FDL composed of three steps: the improved repeated spin-coating of the polyimide (PI) membrane, the secondary mucosal method of silica-framed membrane mirror, and the high-precision fabrication of a multi-level microstructure on a flexible, ultrathin membrane substrate. The results show that the root mean square (RMS) of the wave-front error for M-FDL obtained by the above method is 1/28λ (F# = 8.7 at 632.8 nm) with an 80 mm clear aperture, the average diffraction efficiency is more than 70%, the silica-framed membrane mirror possesses approximately 40 times the overall thermal stability of the traditional metal-framed mirror, and the weight is less than 40 g. The measurement results indicate that the M-FDL has high-optical quality and high-thermal stability and can satisfy the imaging requirements.

Microstructure-based fatigue life modeling methodology for ferritic-pearlitic hypo-eutectoid steels

A microstructure-based fatigue life prediction methodology was proposed and verified for 44MnSiVS6 hypo-eutectoid steel. As a first step, a statistically equivalent synthetic microstructure generation algorithm was developed by applying the cellular automata under the multi-level microstructure generation approach, and verified by comparing to the real microstructure. Crystal plasticity-based elasto-viscoplastic constitutive models were developed for the primary ferrite and pearlite, and their constitutive parameters were calibrated. Synthetic microstructure-based crystal plasticity finite element method (CP-FEM) simulations were performed for stress-controlled axial fatigue tests. The Fatemi-Socie (FS) parameter was chosen to calculate a fatigue indicator parameter increment (ΔFIP) per cycle, and its cumulative distribution probability (CDP) curve was obtained from CP-FEM simulations. Three different criteria extracting a representative ΔFIP from the CDP curve were proposed after thoroughly examining the nature of the CDP curves, which showed the dual transition in the upper CDP range. Extracted representative ΔFIP values coupled with the power law-based model gave reasonable fatigue life prediction. In particular, the best prediction was made when the representative ΔFIP values were taken beyond the second transition of the CDP curve, in which the ΔFIP hot spots were concentrated in the primary ferrite.

Preparation and performance of a self-humidifying fuel cell using a fiber sintered sheet as flow field

The water management problem of fuel cells has been troubled for its further application, and the precision of the existing humidity control strategy is not sufficient to adapt to complex operating conditions. In this study, a new type of porous flow field, based on metal fibers with continuous capillary paths and excellent capillary suction ability, is proposed to retain moisture and enhance the back diffusion of moisture from the cathode to the anode, to achieve self-humidification. These fibers are obtained by turning, and their surface is covered with multi-level microstructure, which greatly increases specific surface area, and the capillary suction capacity of the fibers for water, compared to the ordinary smooth surface structure. Experimental results show that the fiber flow field with an optimal porosity of 70% can operate stably at 50 °C and achieve the best performance when humidified at room temperature. Under atmospheric pressure, the temperature resistance is increased by 5 °C compared to the serpentine flow field, and the limit peak power density is increased by 18.75%.

In situ synergistic strategy of sacrificial intermedium for scalable-manufactured and controllable layered double hydroxide film

Layered double hydroxides (LDHs), a class of two-dimensional (2D) brucite-like layers, have been effectively applied in diverse fields. However, the current synthesis methods restrict the in situ scaling-up and tunable production of LDH-based materials. Inspired by the growing characteristic of “Bryophyllum pinnatum”, a sacrificial co-sputtered Zn−Al transition layer was introduced for the first time to in situ grow a scalable-manufactured and thickness-controllable LDH film on arbitrary substrate materials with flexible shapes through “partial dissolution” and “solution infiltration” processes. Diverse LDH films could be tailored by the creative regulation of the component, structure and surface state of the transition layer. Results showed that the as-prepared LDH film had strong mechanical robustness under harsh abrasion conditions due to its large thickness and multi-level microstructure. Moreover, a series of galvanic couple model experiments based on Zn/Al single-metal transition layers were designed to solve the real-time monitoring issue in the complex hydrothermal solution. This work not only develops a new strategy to design and grow in situ LDH films with multifaceted features, but also reveals sophisticated LDH formation mechanisms. Hence, the findings of this study may broaden the practical application of LDH-based materials toward advanced and smart devices.

Intrinsic heterogeneity of grain boundary states in ultrafine-grained Ni: A cross-scale study by SIMS and radiotracer analyses

Using a correlated diffusion study applying secondary-ion mass spectroscopy (SIMS) and radiotracer analyses, the co-existence of both relaxed and deformation-modified non-relaxed high-angle grain boundaries (GBs) in ultrafine-grained Ni of 2N6 purity processed by equal channel angular pressing (ECAP) is clearly revealed. Due to different depth and lateral resolutions and using experimentally accessible diffusion times, SIMS provides a direct access to the properties of relaxed “slow” GBs (at short penetration depths) while the radiotracer measurements reveal simultaneously the contribution of the deformation-modified “fast” GBs (at large penetration depths). The temperature stability of ultrafine-grained structure of 2N6 Ni is investigated using electron back-scatter diffraction after annealing treatments corresponding to the diffusion experiments. No changes of the ECAP-produced microstructure occur at 403 K, while the ultrafine-grained structure is remarkably evolving to a coarse-grained one at 603 K. The knowledge of the microstructure evolution is used to quantify the diffusion data. The combination of the two complementary techniques allows not only to perform a cross-scale analysis of the mass transport, but also to probe consistently the existence and kinetic properties of different multi-level hierarchic microstructure features. Therefore, the results obtained is a step forward a better understanding of the physics of ultra-fine-grained materials (UFG). For the first time in the case of UFG materials, the SIMS technique is used in a mode with lateral resolution which is correlated with the microstructure characteristics resolving a multi-level hierarchy of diffusion properties of short circuits in severe plastically deformed materials.

Electrospun fiber-based high-performance flexible multi-level micro-structured pressure sensor: Design, development and modelling

• Template-assisted electrospinning is applied to fabricate the multi-level microstructure TPU membranes. • The pressure sensor shows ultralow detection limit, high sensitivity and wide sensing range. • The building block approach is creatively applied in FEA. • The pressure sensors enable real-time human physiological signals. Geometric microengineering is an effective approach to improve the comprehensive performance of pressure sensors. Unfortunately, the design of multi-level microstructure and the development of industrially relevant technology remain challenging. In this study, template-assisted electrospinning is applied to fabricate the multi-level microstructured TPU membranes with both regularly distributed knoll-like microstructures on the surface and randomly distributed fiber-network structures inside, which serve as the active layers of the pressure sensor. The assembled pressure sensor shows exceptional performance, including ultralow detection limit of 0.7 Pa, high sensitivity of 63.93 kPa −1 , a wide sensing range of 0–160 kPa and excellent durability of >10000 cycles. The sensing mechanism is further investigated based on the equivalent circuit diagram analysis and finite element analysis (FEA). In FEA, the building block approach is adopted to simulate the electro-mechanical performance between complex fiber networks. These results reveal that the knoll-like microstructures and fiber-network structures lower the effective elastic modulus and increase the contact points/areas or conductive path upon loading, thereby responsible for the exceptional sensing performance. Real-time monitoring of human physiological signals is demonstrated. The industrial relevance of the template-assisted electrospinning technology for fabricating pressure sensors is highly scalable, thus industrially relevant.

Effect of aging temperature on mechanical properties of TC21 alloy with multi-level lamellar microstructure

This paper aims to reveal the effect of aging temperature on strength, impact toughness and fracture toughness of TC21 alloy with multi-level lamellar microstructure. The multi-level lamellar microstructures of TC21 alloy were prepared by solid solution at 1000 °C, annealing at 800 °C and respectively aging at 550 °C, 600 °C and 650 °C. The multi-level structures include β grains, α colony (αc), primary α phase (αp) and aged α plates (αs). The microstructures were performed on using optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), laser scanning confocal microscope (LSCM) and image analysis software. Results show that as aging temperature goes up, the size of αs increases and the segregation of alloy elements increases, while the β grain, grain boundary α phase (Gα) and αc almost remain unchanged. Hall-Petch formula is used to reveal that αs phase is the minimum control unit of strength. Fine grain strengthening, volume fraction of α phase (Vα) and element segregation have great influence on mechanical properties. In the impact experiment, microstructure deformation and secondary cracks consume more energy, while cleavage fracture consumes less energy. The TEM analysis found that the coordination of microstructure deformation became worse after aging. Fracture analysis shows that the size of αc plays an important role in crack propagation, and the crack propagation path always tends to cut αc vertically and pass through it. Whether the size of αc is large or small, it is not conducive to the increase of crack propagation path. Crack propagation path length and the interface energy consumed by different fracture mechanisms should be taken into consideration when there are more crack propagation paths and the fracture toughness decreases in the multi-level lamellar microstructure of TC21 alloy.

Tunable Wide Range and High Sensitivity Flexible Pressure Sensors with Ordered Multilevel Microstructures

AbstractWith the rapid development of healthcare and human‐machine interactions, there is a growing demand for flexible electronic skin to have a high sensitivity over a wide range. While current multilevel and hierarchical structures inspired by nature broadened the sensing range, the structural design still lacks systematic study. Hereby, an ordered multilevel microstructure is proposed, and the design strategy for performance regulation of piezoresistive pressure sensors is studied. Both microstructure height and spatial distribution are investigated systematically through simulation and experiments. The flexible piezoresistive pressure sensor is fabricated by combining a fast, cost‐effective laser marking technology, molding, and pneumatic spray. The fabricated sensors show high sensitivity (1.5 – 8.3 kPa−1) over a wide range (0.01 – 200 kPa), and have a detection limit of 10 Pa, a response time of below 70 ms, and a mechanical stability over 10 000 cycles. This design and fabrication strategy can be further optimized by combining advanced materials and fabrication systems, and is expected to be applicable for a wide range of flexible materials.