High Tensile Properties Research Articles

Introducing both chemical and structural gradients in AISI 321 stainless steel via aluminizing and laser shock peening for superior properties

Aluminizing is a diffusion based chemical surface treatment on materials to provide excellent protection against high temperature oxidation and corrosion, but is likely to be accompanied by a degradation in mechanical properties. Laser shock peening (LSP) is a superior laser based surface strengthening technique for enhanced mechanical properties. In this study, we focus on combining these two methods on the AISI 321 stainless steel to introduce both chemical and structural gradients for superior properties. Comparative investigation on both the microstructure and mechanical properties of the as received 321 steel, aluminized 321 steel and the aluminizing + LSP processed steel indicated that: (1) A three-layer protective coating was introduced on the surface of the aluminized steel and the concentration of Al decreased gradually from the outermost layer to a certain depth, forming B2-FeAl(Cr) solid solution and Al2O3 in Layer-I, B2-FeAl and DO3-Fe3Al phases in Layer-II and BCC-Fe(Cr,Al) solid solution phase in Layer-III, with B2-NiAl precipitates distributed in Layer-II and Layer-III. (2) After LSP treatment, a dislocation density gradient from the surface to the matrix, dislocation-precipitate interactions and a significant compressive stress were introduced. (3) Though the aluminized steel exhibited a decrease in the high temperature tensile properties compared to that of the as received 321 steel, the aluminizing + LSP processed steel achieved a striking enhancement. The formation of three-layer coating, dislocation density gradient, dislocation-precipitate interactions and the residual stress contribute jointly to gain the yield strength, ultimate strength and fracture elongation up to 265 MPa, 430 MPa and 37.5 % at 620 °C, respectively.

Effects of cold rolling and heat treatment on microstructure and mechanical properties of 15Cr-15Ni ODS austenitic steel

Oxide dispersion strengthened (ODS) austenitic steels are considered as the promising candidate cladding materials application for advanced nuclear energy systems. However, the microstructure of ODS austenitic steels fabricated by mechanical alloying is usually not very homogeneous. Thermal mechanical treatment is an effective method for controlling microstructure of alloys. In this work, the effect of cold deformation and subsequent heat treatments on the improvement of microstructure homogeneous and mechanical property of a 15Cr-15Ni ODS austenitic steel was systemically investigated by means of electron backscatter diffraction, transmission electron microscopy and tensile test. Results show that the average grain size decreased and the distribution of grains was more homogeneous after optimized thermal mechanical treatment. The deformation of cold rolling and heat treatment temperatures shows obvious influence on the average size of dispersion particle, the proportion of high angle grain boundary, Schmidt factor and tensile property of 15Cr-15Ni ODS austenitic steel.

Biodegradable implant application: Electrodeposition of HA/TiO2/ZrO2 coating onto Zn-composite substrates

Zinc has currently emerged as a promising biodegradable metal due to its good biocompatible property and promising degradation behaviour. Additionally, inadequate mechanical strength and a lower cell viability value fall short of what is needed for biodegradable implants. In this work, we used the stir-casting process to create a biodegradable Zn-1Mg-1Cu-1HA (ZHA) and Zn-1Mg-1Cu-1ZrO2 (ZZR) composite onto which ceramics composite coating is done by electrodeposition technique to enhance the biocompatibility. The as-cast sample has uniformly distributed fine MgZn2 and CuZn2 phases in a α-Zn matrix, according to microstructural analysis. The mechanical test confirms that ZZR composite exhibited high tensile and compressive properties, including compressive yield strength of 369.562 MPa, a yield tensile strength of 88.725 MPa and ultimate tensile strength of 116.21 MPa. The result of potentiodynamic polarization test shows that the coated ZZR composite sample gives a corrosion rate value of 0.112 mm/year. From immersion tests, the degradation rate obtained a much lower value after immersing the sample in PBS solution for 55 days (0.067 mm/year). Moreover, an extract of coated ZZR composite shows good cell viability in comparison to the uncoated sample at a concentration of 25%, 50% and 75%. Also, the hemolysis percentage for coated ZZR sample is lower than the other prepared uncoated sample (3.072%) Overall, the result obtained proves that the coated ZZR composite sample can be expected as a capable material for implant application.

High-strength polyvinyl alcohol-based hydrogel by vermiculite and lignocellulosic nanofibrils for electronic sensing

Abstract The use of natural polysaccharides in stretchable hydrogels has attracted more and more attention. However, pure polyvinyl alcohol (PVA) hydrogel has poor mechanical properties and low sensitivity in strain sensors. Composite hydrogels with high tensile properties (the storage modulus of 6,397.8 Pa and the loss modulus of 3,283.9 Pa) and high electrical conductivity (1.57 S·m−1) were prepared using a simple method. The Fe-vermiculite and lignocellulosic nanofibril-based hydrogels were applied as reliable and stable strain sensors that are responsive to environmental stimuli. The prepared hydrogels exhibited excellent ionic conductivity, which satisfied the needs of wrist flexion activity monitoring. The results showed that the PVA/LF0.4 hydrogel has a natural formulation, high mechanical strength, and electrical conductivity, which has great potential for application in artificial electronics.

Flexible MXene‐Based Hydrogel Enables Wearable Human–Computer Interaction for Intelligent Underwater Communication and Sensing Rescue

AbstractConductive hydrogels have recently attracted extensive attention in the field of smart wearable electronics. Despite the current versatility of conductive hydrogels, the balance between mechanical properties (tensile properties, strength, and toughness) and electrical properties (electrical conductivity, sensitivity, and stability) still faces great challenges. Herein, a simplified method for constructing hydrophobic association hydrogels with excellent mechanical and electrical properties is proposed. The prepared conductive hydrogels exhibit high tensile properties (≈1224%), high linearity in the whole‐strain–range (R2 = 0.999), and a wide strain sensing range (2700%). The conductive hydrogel can realize more than 1000 cycles of sensing under 500% tensile strain. As an application demonstration, an underwater communication device is assembled in combination with polydimethylsiloxane/Triton X‐100 film coating, which successfully transmits underwater signals and provides warning of potential hazards. This study provides a new research method for developing underwater equipment with excellent mechanical properties and sensing properties.

Hybrid cross-linked sodium carboxymethyl starch/polyacrylamide flexible sensing hydrogels with adhesion, antimicrobial properties and multiple responses

Ionic hydrogels used as ideal and flexible strain sensor materials should have excellent mechanical, adhesive and antimicrobial properties. However, it is challenging to achieve these multifunctional requirements simultaneously. Herein, we designed and prepared a multifunctional ionic hydrogel with a multi-length tentacle bentonite backbone to initiate the free radical polymerization of acrylic acid bentonite (AABT) and acrylamide (AAm). The interactions of covalent cross-linking, hydrogen bonding cross-linking, charge interactions and physical entanglement between hybrid polyacrylamide-AABT (PAAm-AABT), sodium carboxymethyl starch (SCMS) and PAAm form an multi-in-one hybrid supramolecular network hydrogel (CABZ). This CABZ ion-conductive hydrogel is capable of detecting weak deformation with a detection limit of 1 % strain, high tensile properties of 995 %, excellent strength of 254.5 kPa, fast response (≈0.21 s), high sensitivity of 0.86 and high conductivity of 0.37 S/m. In addition, this CABZ ion-conductive hydrogel has impressive adhesion properties with shear adhesion strength up to 50.78 kPa and broad-spectrum antibacterial properties achieved by AABT-loaded ZnO nanoparticles. Through special AABT hybrid cross-linking, the CABZ ion-conductive hydrogel achieves stable mechanical properties, highly sensitive signal response and antimicrobial properties, which will make it a good choice for flexible wearable sensor materials.

Highly thermally conductive and insulating PET nonwoven fabric/PDMS sandwich composite film by synergism of boron nitride nanosheets and alumina particles

AbstractThe accumulation of heat in electronic devices puts forward an urgent demand for thermal interface materials. It is still a great challenge to achieve the good comprehensive performance of high thermal conductivity (TC), insulation, flexibility and tensile strength. In this work, polyester‐based nonwoven fabric (NWF) was coated with boron nitride nanosheets (BNNS) by dispersion and interfacial reinforcement of cellulose nanofibers to obtain a three‐dimensional thermally conductive network skeleton (BNNS@NWF). The sandwich‐structured composite film was assembled by introducing alumina (Al2O3)/polydimethylsiloxane (PDMS) layers on the top and bottom surfaces of BNNS@NWF using scratch coating and hot pressing processes. The composite film has a high TC of 6.42 W/mK at 45.8 wt% BNNS content, and has excellent insulation with a volume resistivity of 1.06 × 1015 Ω cm. This is due to the long‐range effective thermal conduction path constructed by BNNS, the bridging effect of Al2O3 and the synergistic effect of the two fillers. PDMS helps the composite film maintain good flexibility and good TC stability after 30 bending cycles. The PET nonwoven interlayer gives the composite film good mechanical properties with a tensile strength of 17.5 MPa. This work provides a strategy for the efficient preparation of flexible composite films with high TC and insulation properties, which is of great importance for the development of innovative thermal interface materials.Highlights A sandwich‐structured composite film was prepared by a simple scale‐up method. Al2O3 and BNNS achieves synergistic enhancement of thermal conductivity. The film has a high thermal conductivity of 6.42 W/mK and electrical insulation. The film shows good flexibility, high tensile and thermal management properties.

Triple‐network‐based conductive polymer hydrogel for soft and elastic bioelectronic interfaces

AbstractConductive polymer hydrogels have greatly improved the compatibility of electronic devices with biological tissues for human–machine interfacing. Hydrogels that possess low Young's modulus, low interfacial impedance, and high tensile properties facilitate high‐quality signal transmission across dynamic biointerfaces. Direct incorporation of elastomers with conductive polymers may result in undesirable mechanical and/or electrical performance. Here, a covalent cross‐linking network and an entanglement‐driven network with conductive poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have been combined. The triple‐network conductive hydrogel shows high stretchability (with fracture strain up to 900%), low impedance (down to 91.2 Ω cm2), and reversible adhesion. Importantly, ultra‐low modulus (down to 6.3 kPa) and strain‐insensitive electrical/electrochemical performance were achieved, which provides a guarantee for low current stimulation. The material design will contribute to the progression of soft and conformal bioelectronic devices, and pave the way to future implantable electronics.

Recycle of bio‐waste banana and sisal fiber filled harmlessness epoxy hybrid composite for automotive roof application

AbstractInsists of polymer matrix composite is prepared by using natural fiber facilitates high tensile, flexural, and impact toughness properties. The natural fiber utilization in the polymer matrix can overcome the synthetic fiber demerits of poor compatibility, high moisture absorption, and high cost. The present research investigates developing a low‐cost, environmentally eco‐friendly epoxy hybrid composite using different volume percentages of chopped natural waste banana (0Vol%, 5Vol%, 10Vol%, and 15Vol%) and sisal fiber (0Vol%, 15Vol%, 10Vol%, and 5Vol%) through hand mould hot compression technique. The presence of natural waste banana and sisal fiber on tensile strength, flexural strength, and thermal adsorption properties of the epoxy hybrid composite are evaluated by ASTM test standards. The ASTM standard measured test results of epoxy hybrid composite with and without natural waste banana and sisal fiber were compared and sample three was identified by good tensile strength, flexural strength, and better thermal adsorption properties compared to all others. The sample three epoxy hybrid sample is recommended for automotive roof application.

Effect of processing route on microstructure and tensile properties of hot isostatic pressed 30CrMnSiNi2A steel: Comparison of prealloy and master alloy routes

The prior particle boundaries (PPBs) are non-negligible powder metallurgy defect, which seriously weaken the mechanical properties of hot isostatic pressed (HIPed) steels. In present study, the master alloy route is proposed to improve the PPBs in HIPed 30CrMnSiNi2A steel, and the Fe-4.40Cr-4.80Mn-4.60Si-6.80Ni-1.00Mo-0.40V-1.12C master alloy system with low solidus temperature and wide solid-liquid temperature interval is designed. The microstructure, tensile properties and fracture behavior of HIPed compacts prepared by prealloy and master alloy routes are systematically compared. The results show that the structure in prealloyed sample is granular bainite (GB); and substantial Si oxides distributed along particle boundaries constitute serious PPBs. The yield strength (YS), ultimate tensile strength (UTS) and total elongation (TE) of the sample are 723 ± 10 MPa, 1238 ± 16 MPa and 12.3 ± 0.4%, respectively. In master alloy route, the formation of local liquid disrupts the distribution of Si oxides along particle boundaries and promotes the coarsening of oxides, which results in dispersed distribution of oxides and significant reduction in oxide density. In addition, since the structural uniformity depends on element diffusion, a relatively uniform structure is obtained through the optimization of powder size. The structure of optimized sample mainly consists of GB and martensite; and good tensile properties with YS of 798 ± 7 MPa, UTS of 1310 ± 8 MPa and TE of 15.3 ± 0.6% are obtained. The higher tensile properties are mainly due to the improvement of PPBs, which avoids the initiation of microcracks along PPBs and further avoids premature failure of material.

Effects of Fe and Ni on the Microstructure and High Temperature Tensile Properties of Al-Si Aluminium Alloys

The effects of varied contents of Ni (1.2 wt.%, 1.6 wt.%) and Fe (0.6 wt.%, 0.8 wt.%) on the microstructure and high temperature mechanical properties of Al-Si alloy were studied using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and tensile testing machine. The experimental results demonstrate that Ni element plays a crucial role in modifying the Fe-rich phase type, morphology and distribution in the Al-Si alloy. The addition of 1.2 wt.% Ni and 0.6 wt.% Fe could generate a Chinese script Fe-rich strengthening phase in Al-Si alloy. Further increasing to 1.6 wt.% Ni and 0.8 wt.% Fe, the long needle-shape Fe-rich phase was detected. High temperature tensile properties of the alloy were significantly improved, because of the Chinese script Fe-rich strengthening phase in the Al-Si alloy containing 1.2 wt.% Ni and 0.6 wt.% Fe. The ultimate tensile strength (UTS) of Al-Si alloy with 1.2 wt.%Ni-0.6 wt.% Fe is up to 229 MPa, 174 MPa and 139 MPa at 250 °C, 300 °C and 350 °C, respectively.

Sealing characteristics of aramid fiber reinforced rubber gasket with scratch depth and width defects

AbstractNon‐asbestos gaskets have high tensile properties, good permeability resistance, and resilience. Compared with traditional asbestos gaskets, non‐asbestos gaskets have the advantages of less pollution and no harm to human body. This manuscript presented an experimental and theoretical study of aramid fiber reinforced non‐asbestos gaskets. The tensile strength of gaskets with different fiber orientations and tensile rate were conducted in order to meet the industrial standard. The leakage rates of nondestructive non‐asbestos gaskets with different sizes under different medium pressures and pretightening load were investigated. The results showed that the leakage rate can reach the industrial standard when the pretightening load reached 30 MPa and medium pressures was less than 2 MPa. The artificial scratch defects were made on non‐asbestos gaskets, and the effect of the width and depth of the scratch defect on leakage rate was further investigated. The sealing failure would occur when the scratch depth reached 0.1 mm. The modified model containing defect factors was established. The results showed that the modified model can well characterize leakage rate of gasket.

Investigating the Effect of Curing Activators on the Cure Kinetics of Acrylonitrile–Butadiene Rubber Filled with Graphene Oxide and Reduced Graphene Oxides Nanocomposites

For the first time, acrylonitrile–butadiene rubber (NBR)–graphene oxide (GO) and reduced graphene oxide (rGO) composites were prepared without cure activators: zinc oxide/stearic acid (ZnO/SA) and studied. The vulcanization characteristics of the compounds were systematically studied at 160–190°C, with the aid of rheometer and differential scanning calorimetry (DSC) techniques. NBR revealed rapid curing time (t90) with greater cure rate index compared with NBR–GO/rGO composites for the rheometer measurement. This results were in correspondence with the activation energies Ea (kJ/mol) calculated by Ozawa and Kissinger models of vulcanization kinetics. NBR–rGO obtained reduced t90 and Ea (kJ/mol) than NBR–GO, perhaps due to lower oxygenated groups: epoxide (–C–O–C–), carboxyl (–O–C=O), and hydroxyl (–OH) present. Although, the composites delayed in curing, they significantly recorded high tensile properties with high reinforcing factors than NBR. The order of increasing mechanical properties: NBR < NBR–rGO < NBR–GO followed the same order of increasing crosslinking density. In terms of tensile strength, NBR–GO-1 obtained 62.5% and 18.2% increment than NBR and NBR–rGO-1, respectively. The findings from this study indicate that the absence of ZnO/SA in rubber compounds may slow down curing of rubber–GO/rGO composites and lower networks compared with those containing activators ZnO/SA. However, optimization of ZnO/SA and with desired functional groups on graphene and derivative graphene sheets (GDS) including other proposed factors may enhance the curing speed of rubber–GDS based systems, without compromising their mechanical integrity for advanced applications.

Simulation of Tetrahedral Profiled Carbon Rovings for Concrete Reinforcements.

Textile reinforcements are increasingly establishing their position in the construction industry due to their high tensile properties and corrosion resistance for concrete applications. In contrast to ribbed monolithic steel bars with a defined form-fit effect, the conventional carbon rovings' bond force is transmitted primarily by an adhesive bond (material fit) between the textile surface and the surrounding concrete matrix. As a result, relatively large bonding lengths are required to transmit bond forces, resulting in inefficient material utilization. Novel solutions such as tetrahedral profiled rovings promise significant improvements in the bonding behavior of textile reinforcements by creating an additional mechanical interlock with the concrete matrix while maintaining the high tensile properties of carbon fibers. Therefore, simulative investigations of tensile and bond behavior have been conducted to increase the transmittable bond force and bond stiffness of profiled rovings through a defined roving geometry. Geometric and material models were thus hereby developed, and tensile and pullout tests were simulated. The results of the simulations and characterizations could enable the optimization of the geometric parameters of tetrahedral profiled rovings to achieve better bond and tensile properties and provide basic principles for the simulative modeling of profiled textile reinforcements.

Formation of dendrites and strengthening mechanism of dual-phase Ni36Co30Fe11Cr11Al6Ti6 HEA by directional solidification

In order to reveal the effect of solidification rate on microstructure and improve room and high temperature tensile properties, Ni36Co30Fe11Cr11Al6Ti6 high entropy alloys (HEAs) were prepared by directional solidification at different solidification rates (5, 10, 20, 50 and100 μm/s). Results show that two kinds of dendrite form in the directionally solidified process. One is primary solidified dendrite, which is composed of FCC1 phase enriched in Co, Cr and Fe. Another is secondary solidified dendrite, forming between the primary solidified dendrites and consisting of the FCC2 phase enriched in Ni, Al and Ti. As the solidification rate increases, the primary solidified dendrite spacing decreases, the solute enrichment layer overlaps, and the constitutional undercooling in the inter-dendrite region decreases, increasing the difficulty of the secondary solidified dendrite formation. Tensile results show that the strength of Ni36Co30Fe11Cr11Al6Ti6 HEAs gradually increases with the increase of solidification rate. The alloy with a solidification rate of 100 µm/s exhibits excellent comprehensive room temperature properties, the yield strength, fracture strength and tensile strain are 732 MPa, 1020 MPa and 34.9 %, respectively. Furthermore, the directionally solidified Ni36Co30Fe11Cr11Al6Ti6 HEA still remains high yield strength of 533 MPa at 900 ℃. Fine grain strengthening, solid solution strengthening, second phase strengthening and hysteresis diffusion effects play an important role in enhancing the mechanical properties. By comparing the mechanical properties of other HEAs at room and high temperature, the proposed directionally solidified Ni36Co30Fe11Cr11Al6Ti6 HEAs with excellent mechanical properties show great potential in industrial applications.

Improved Tensile and Bond Properties through Novel Rod Constructions Based on the Braiding Technique for Non-Metallic Concrete Reinforcements

Textile reinforcements have established themselves as a convincing alternative to conventional steel reinforcements in the building industry. In contrast to ribbed steel bars that ensure a stable mechanical interlock with concrete (form fit), the bonding force of smooth carbon rovings has so far been transmitted primarily by an adhesive bonding with the concrete matrix (material fit). However, this material fit does not enable the efficient use of the mechanical load capacity of the textile reinforcement. Solutions involving surface-profiled rods promise significant improvements in the bonding behavior by creating an additional mechanical interlock with the concrete matrix. An initial analysis was carried out to determine the effect of a braided rod geometry on the bonding behavior. For this purpose, novel braided rods with defined surface profiling consisting of several carbon filament yarns were developed and characterized in their tensile and bond properties. Further fundamental examinations to determine the influence of the impregnation as well as the application of a pre-tension during its consolidation in order to minimize the rod elongation under load were carried out. The investigations showed a high potential of the impregnated surface-profiled braided rods for a highly efficient application in concrete reinforcements. Hereby, a complete impregnation of the rod with a stiff polymer improved the tensile and bonding properties significantly. Compared to unprofiled reinforcement structures, the specific bonding stress could be increased up to 500% due to the strong form-fit effect of the braided rods while maintaining the high tensile properties.

Multifunctional double-network Ti3C2Tx MXene composite hydrogels for strain sensors with effective electromagnetic interference and UV shielding properties

The advent of hydrogel-based flexible strain sensors has generated enormous research interest due to their outstanding biocompatibility. However, developing hydrogel-based strain sensors with high gauge factor, wide detection range and multifunctional integration is still challenging. Here, a novel multifunctional hydrogel-based strain sensor is composed of two-dimensional transition metal carbides/nitrides (Ti3C2Tx MXene) and Polyacrylamide-co-Poly-N-hydroxyethylene acrylamide/Carboxy Methyl Cellulose-Fe3+ dual network structure (PAAm-PHEMAA/CMC-Fe3+) with multiple hydrogen bonds and coordination interactions. The dual network design endowed the hydrogel-based human motion sensor with fast rebound and high tensile properties, enabling it to exhibit high sensitivity (response time ∼120 ms and gauge factor ∼1.62), and a wide detection range (0–700%), including joint movements as well as more subtle human motions (facial micro-expression changes and speech). More importantly, the hydrogel-based strain sensor exhibited excellent EMI (41 dB, X-band) and UV shielding properties (365 nm, 100%, 0.5 mm) due to the synergy of porous structure, moderate conductivity, and ionic solution environment. Moreover, it demonstrated robust adhesion (29 kPa), high shape adaptability, and self-healing capability. This innovative multi-functional flexible sensor design provides guidance for the development, research and application of high-performance flexible wearable materials.

Complex-chamber hydrogel actuators based on strong interfacial adhesion for fluid-driven multi-degree-of-freedom motions

Hydrogel actuators with fast responsive speed, large driving power, diverse motions, superior mechanical properties and good environmental adaptability could be a suitable candidate for complex-task scenarios. However, a complete aggregation of these above characteristics is rarely reported, due to limitations from processing methods, raw materials and structural configuration of present hydrogel actuators. Herein we designed and fabricated complex-chamber-structure hydrogel actuators basing on soft interfacial adhesion of aluminum hydroxide nanocomposite hydrogels without any mold, template and valuable equipment, demonstrating that this method possessed simple, facile and inexpensive features. These composite hydrogels showed high tensile (0.5–1.0 MPa) and compressive (2–15 MPa) resistance properties, much higher than those of previously reported fluid-driven hydrogel actuators, which meant that our hydrogel actuators could have a higher cargo loading capacity. The cavity-structure soft actuators owned superior sealability and self-recoverability, and could give rapid uniaxial expansion and multidirectional large-scale bending under fluid actuation. Furthermore, those actuators with sucker structure were able to transfer heavy objects (e.g. 80 g glass plate and 180 g billiard ball) from water to air, and also move a plastic plate from back to right in three-dimensional space, indicating that this complex-cavity hydrogel actuators could suit to multi-task scenarios. The exquisitely assembled process of intricate chamber structure will offer a novel approach for hydrogel actuators with diversified driving functions.

Crosslinked reprocessable phosphor/polyurethane composite networks with thermal induced self-healing capacity and ultraviolet conducted fluorescence effect

In recent years, self-healing materials have attracted extensive attentions, however, the low elasticity have limited their applications, and it is difficult to track their healing process on macroscale. Herein covalently crosslinked polyurethane (PU) composite networks were developed with thermal induced self-healing capability and ultraviolet (UV) initiated fluorescence effect, which were synthesized by polytetrahydrofuran glycol (PTMG) as soft segment, hexamethylene diisocyanate (HDI) as hard segment, incorporating with blue phosphate (BP) of SrAl2O4 doped with Eu2+, Dy3+. The physio chemical properties and self-healing process of polyurethane were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), atomic force microscope (AFM), optical microscope (OM), dynamic mechanical analysis (DMA) and tensile test. The results showed that the network materials were successfully developed with high elastic tensile properties. After healing at 60 °C for one hour, the PU network demonstrated a high healing efficiency and elongation at break. Moreover, the obtained hybrid networks emitted an intense blue light under UV with high fluorescent intensity to track healing process. Additionally, the synergistic effect of transesterification of dynamic hydrogen bond provided the composite networks reproducibility for recycling use. This self-healing polyester material shows promising applications in the fields of diagnostic healing and optoelectronic components.

Microstructure characterization and mechanical properties of the 304SS-(NiTif/FeAl) metal-intermetallic laminate composites

In this work, a novel continuous NiTi Shape Memory Alloy Fiber Reinforced (SMAFR) B2-FeAl based metal-intermetallic laminate (MIL) composite was prepared via two-step vacuum hot pressing combined with “multi-thin foils” stacking configuration. The microstructure characterization of the composite was conducted by using X-ray diffractometer, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. The compressive and tensile properties of the composites were measured. Results indicated that the SMAFR MIL composite exhibits multi-layer structure consisting of residual stainless steel layer, newly-formed intermetallic layer and intermediate transition layer. The intermetallic layer is composed of several sublayers with the boundaries of centerlines, and B2-FeAl phase is the main phase in this layer. NiTi fibers locate at the centerlines in the intermetallic layer and show a uniform distribution. A metallurgical interfacial bonding between NiTi fiber and FeAl matrix was obtained through the inter-diffusion of Ni, Ti and Al elements across the interface. In the intermediate transition layer, B2 phase was also the dominant phase, and a large amount of fine Al-rich precipitates dispersed in the matrix. Compared with the MIL composite without NiTi fibers, the SMAFR MIL composite possesses superior compressive and tensile properties, which are mainly attributed to (Ⅰ) high tensile properties of NiTi fiber, (Ⅱ) a good interfacial bonding of NiTi/B2-FeAl, (Ⅲ) strong interfacial reaction products, and (Ⅳ) pullout effect of NiTi fibers.