Interlamellar Spacing Research Articles

Microstructure and strength in ultrastrong cold-drawn medium carbon steel

Via traditional wire drawing, the medium carbon ferrite-pearlite (MCFP) steel wires can achieve the ultrahigh strength beyond 4 GPa normally for high-carbon pearlitic steel wires, but have a 30–60% lower production cost. The microstructural evolution and mechanical properties of medium carbon ferrite-pearlite steel wires have been investigated by means of scanning electron microscopy, transmission electron microscopy and tensile testing. The tensile strength of medium carbon ferrite-pearlite steel wires increases from 750 MPa up to 4120 MPa when the drawing strain increases up to ε = 6.4, which represents the highest strength reported so far – to our knowledge for a carbon steel with such low carbon content. At low and medium strains (ε ≤ 1.95), the proeutectoid ferrite forms dense dislocation walls (DDWs) via dislocation activities, including sliding, accumulation, interaction, and tangling. With the drawing strain increase, the reorientation of DDWs to the drawing direction forms the coarse proeutectoid ferrite lamellae. Finally, the proeutectoid ferrite deformed to high strains is characterized by a lamellar morphology and the average lamellar spacing of proeutectoid ferrite is about 55 nm at ε = 6.4. The interlamellar spacing of pearlite and thickness of cementite decreases with the drawing strain increases. The dislocation density in ferrite lamellae increases with the drawing strain increases, and the dislocation density in ferrite lamellae is 7.8 × 1015 m−2 at ε = 4.19. A higher dislocation density of 3.1 × 1016 m−2 can be obtained at ε = 6.4 by means of extrapolation and TEM investigations. The stress contributions of proeutectoid ferrite and pearlite to the flow stress are estimated based on quantified structural parameters. Based on the assumption that the stress contributions from different strengthening mechanisms are linearly additive and the general rule of mixtures, a good agreement between the measured and estimated flow stresses has been found in a large range of flow stress. The good application of the general rule of mixture to the medium carbon ferrite-pearlite steel wires indicates the importance of quantitative characterization of microstructural evolution and parameters with the strain.

Expanding the interlamellar spacing of biomass-derived hybrids with intercalated nanotubes for enhanced oxygen reduction reaction

An efficient method has been designed for creating mesopores in electrocatalysts using in situ grown CNTs.

Effect of Niobium on Microstructure and Mechanical Properties of a Hypereutectoid Steel

High-carbon steels have been used to high-strength steel wire and strands for prestressing concrete. The necessity of high-strength levels at increasingly larger diameters of wire rods is a technological challenge. Two steels with and without Nb were obtained in a steel mill, submitted to detailed microstructural (previous austenitic grain size, pearlite interlamellar spacing and colony size) and mechanical characterization through tensile tests and hardness. Hot torsion and dilatometry tests were performed to simulate steels processing and to verify the influence of Nb on phase transformation. Adding Nb to steel resulted in a refinement in austenitic grain size and pearlite colonies but had no effect on pearlitic interlamellar spacing. There was a decrease at the start transformation temperature austenite/pearlite and therefore an increase in the hardenability of the Nb-added steel. Finally, Nb addition proved to be a technical and economical way to increase tensile strength and to reduce the variability of the mechanical properties.

Crevice corrosion of U75V high-speed rail steel with varying crevice gap size by in-situ monitoring

Crevice corrosion of high-speed rail steel U75V was studied with varying gap size by using self-designed device. Increasing gap size inhibited exterior cathodic reduction reaction of oxygen, inducing decrease of potential difference between interior and exterior. Gap size decrease after increase induced increase of potential difference after decrease, not completely reversible because rust kept expanding, acting as weaker depolarizer than oxygen. Anodic dissolution of interior was under ohmic-control, fastest near crevice mouth and slowest near but not at deepest site. Corrosion initiation was observed, closely related to pearlite nodules with larger interlamellar spacing and different lamellar directions, inducing deep attack.

Evading the strength-ductility trade-off at room temperature and achieving ultrahigh plasticity at 800℃ in a TiAl alloy

Improving the room temperature (RT) strength/ductility and hot-working capacity based on lamellar microstructures is of great significance for the practical application of TiAl alloys. However, the microstructure of these alloys has not been clearly identified yet. In this work, two new microstructures, here named triple-phase triple-state (T-T) and triple-phase dual-state (T-D) structures, were developed using a two-step heat treatment process in the Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloy, which also contains the pearlitic-like microstructure (PM) transformed through triggering a massive cellular response (CR). These two microstructures significantly improved the alloy strength. Furthermore, their ductility at RT and 800 ℃ was enhanced twice and 5, 6 times with respect to that of the lamellar microstructure with nano-scale interlamellar spacing, respectively. It was revealed that the formation of abundant deformation twins and their intersections in PMs during plastic deformation, cause prominent strain hardening and the dynamic Hall-Patch effect. This results in a simultaneous improvement of the RT strength and plasticity and promotes dynamic recrystallization at temperatures lower than 800 ℃; thus, the plasticity is dramatically enhanced at elevated temperatures. This structural design strategy should be extendable to other TiAl systems that can undergo a CR and provides a promising new pathway for solving the severe engineering challenges caused by the low RT plasticity and poor hot-working capacity of TiAl alloys.

Rapid solidification of AlCoCrFeNi2.1 High-entropy Alloy

In this work the effect of cooling rate on the dual-phase (L12/B2) AlCoCrFeNi2.1 Eutectic High-Entropy Alloy was investigated. AlCoCrFeNi2.1 powders were made using a drop-tube facility, achieving powders of sizes ranging from 850 µm ≤ d < 1000–38 µm ≤ d < 53 µm with corresponding estimated cooling rates of 114 Ks−1 to 1.75×106 K s−1 respectively. Average interlamellar spacing decreases from 2.10 µm in the as-cast alloy to 348 nm in the powders of the 38 µm < d < 53 µm size fraction. Although decreased interlamellar spacing is expected to enhance microhardness, such a relation was not as strong as expected, with microhardness of the powders found to vary only slightly from an average value of 340 Hv0.03. This unexpected result is explained via the observation of increased FCC volume fraction. With increasing cooling rate, the microstructure of AlCoCrFeNi2.1 was found to evolve gradually from regular eutectic to colony eutectic, followed by dendritic with eutectic the interdendritic regions. In particles of size d < 212 µm BCC dendrites were observed, either dominating the structure or coexisting with FCC dendrites.

Micro-axial cracking in unnotched, cold-drawn pearlitic steel wire: Mechanism and beneficial effect on the resistance to hydrogen embrittlement

Effects of cold drawing ratio (CDR) on the microstructure, tensile properties, H absorption and hydrogen embrittlement (HE) of pearlitic steel wire were investigated by means of thermal desorption analysis, slow strain rate tensile testing, fractography and silver decoration. The ultimate tensile strength (UTS) and diffusible H content of unnotched tensile specimens were raised with increasing CDR due to the reduction of interlamellar spacing and the increase in dislocation density. Nevertheless, the resistance to HE was improved as the CDR became above 30% due to micro-axial cracking. Elongations of H-uncharged and charged specimens decreased until the CDR of 30%, and then were maintained despite of a continuous rise of UTS with increasing CDR further. This is because micro-axial cracking occurred in the specimens with CDRs above 30% so that tensile fracture was retarded. As the CDR was over ∼30%, a fracture mode changed from brittle fracture featured by tearing topography surface and cleavage to ductile-like fracture characterized by many dimples and micro-axial cracks. Micro-axial cracking occurred as follows: Some micro-cracks preexisted inside well-aligned pearlite colonies of specimens with CDRs above 30%. While an unnotched, H-uncharged specimen was strained, micro-cracks additionally formed to be coalesced. The merged cracks traversed the pearlite colonies to be propagated into neighboring misaligned colonies and grew along the direction of cold drawing and tensile deformation, resulting in micro-axial cracking. In H-charged specimens, H atoms near micro-cracks clustered into micro-cracks so that micro-axial cracking was accelerated and the regions near micro-cracks underwent ductile fracture, leaving many dimples.

In-situ Li+insertion induced lithiophilic expansion graphite for dendrite-free lithium metal anode

For the most ordinary graphite negative electrode, the inserted Li+ occupies interlamellar spacing in the graphite lattice, and transform into Li-graphite phase (LiXC6). During the high charging rates, Li+ is adsorbed preferentially on lithiated LiXC6 which promotes Li crystallization and grows into uncontrollable dendrites. Thus, how to apply this defect to advantage and extend into stabilizing Li metal plating is ignored in practice. Herein, expansion graphite (EG) is ornamented as lithiophilic porous carbon basement which leverages insertion Li+ as inducing sites. In this way, Li metal grows preferentially on the lithiated graphite layer and ensuring the plating/stripping stably and suppressing the growth of lithium dendrites. Consequently, a stable polarization of 49.5 mV is obtained with EG anode in a symmetrical cell with 320 h even at a high current density of 10 mA cm−2 and high areal capacity of 10 mAh cm−2. Additionally, the resulting EG@Li assembled LFP full cell could deliver 85% capacity retention after 500 cycles.

Additive manufacturing of high-strength eutectic aluminium-nickel alloys – Processing and mechanical properties

The application of additively manufactured high strength aluminium base alloys is, among others limited due to either a lack in processability or economic feasibility with the alloys currently available. Within this work, the mechanical properties of additively manufactured eutectic Al-Ni alloys are investigated for the first time. With an average ultimate tensile strength of 545 MPa at an elongation at failure of 10.1 %, Al-7.5 wt. % Ni-2.0 wt. % Cu (AlNi7.5Cu2.0) is the first aluminium base alloy known to the authors that has been processed with Laser Powder Bed Fusion (LPBF) and surpasses an ultimate tensile strength of 500 MPa and an elongation at failure of 10 % while relying on economically feasible alloying strategies and elements (i.e. no addition of rare earth elements, such as Sc). The properties of the alloys investigated are assumed to be a consequence of the α-aluminium- and intermetallic Al 3 Ni-phase comprising the eutectic in combination with an ultrafine interlamellar spacing as a result of the cooling rates utilized in the LPBF process. The specific alloy compositions investigated in this work are Al-7.5 wt. % Ni (AlNi7.5), Al-7.5 wt. % Ni-0.5 wt. % Cu (AlNi7.5Cu0.5) and AlNi7.5Cu2.0. All alloys were manufactured crack free by LPBF with part densities >99.9 %. For the binary AlNi7.5 alloy, an average ultimate tensile strength of 484 MPa was determined at an elongation at failure of 5.4 % in the additively manufactured condition. The determined mechanical properties were continuously increased by addition of up to 2.0 wt. % copper.

Investigation on microstructure and mechanical properties of heat-treated Ti-47.5Al–3Nb-3.5Cr alloy

Three heat treatment processing routes (heat treatment at 1300 °C, 1350 °C and 1400 °C for 15min, 30min and 60min respectively, and following air cooling) were developed to investigate the dependence of mechanical properties on microstructure evolution in a new Ti-47.5Al–3Nb-3.5Cr (at.%) alloy. When the heat treatment temperature approaching the solution precipitation temperature of γ phase (Tγ-sol) (Tγ-sol<1300 °C), the interlamellar spacing is found to increase obviously. Moreover, when the heat treatment temperature is between α phase transition temperature (Tα) and Tγ-sol (1400 °C < Tα), the interlamellar spacing and average grain size decreases, the distribution of the B2 phase is more uniform. The Vickers hardness test shows that the Vickers hardness of the heat-treated samples are improved compared with the as-cast sample (352.6Hv). The best Vickers hardness of lamellar microstructure after heat treatment is 465.2Hv. The tensile test at room temperature shows that the good tensile strength and elongation at failure of the heat-treated sample can be obtained after air cooling at 1400 °C for 60min, which are 359.54 MPa and 2.04%, respectively. Compared with 405.06 MPa and 0.66% of the as-cast sample, heat treatment can significantly increase the elongation of the sample. Meanwhile, the observation of the microstructure also exhibits the dependence of microstructure on the mechanical properties. The results shows that the improvement of Vickers hardness is mainly attributed to solid solution strengthening. In addition, the distribution of B2 phase, the refinement of the interlamellar spacing and the average grain size play essential roles in the improvement of the tensile strength and elongation at failure.

Abstract 13462: Assessment of the Physiological and Pathological Structural Differences Along the Aorta in a Rat Model of Metabolic Syndrome

Introduction: Vascular geometry may vary along the aortic length in normal and chronic disease conditions such as metabolic syndrome. Aim: This study investigated regional structural changes in the aorta in a rodent model of metabolic syndrome, the high-fat diet streptozotocin-induced diabetes mellitus (HFD-D). Methods: Four-week-old male Wistar albino rats received a control diet (CD) or high fat diet (HFD) for 10 weeks. On week 6, 40 mg/kg streptozotocin and its buffer were injected intraperitoneally into the HFD and CD groups, respectively. Glucose and insulin tolerance tests (GTT and ITT) and tail-cuff systolic blood pressure (SBP) were measured. At the end of the study, rats were euthanized, and the thoracic and abdominal aortic segments collected for histomorphometric analysis of aortic media thickness, medial cross-sectional area (CSA), elastic lamellae number, interlamellar spacing, collagen density and lipid deposit density. Results: HFD-D rats showed elevated GTT, ITT and SBP. Abdominal aortic segments of both CD and HFD-D rats showed smaller media thickness and CSA, lower elastin lamellae number and higher collagen density compared with the thoracic segments, suggestive of physiological rather than pathological structural differences in both groups. Elastin interlamellar spacing and lipid plaque deposits were higher in the abdominal aorta of the HFD-D relative to controls, indicating that early vascular pathological changes favor the abdominal aorta in HFD-D rats. Conclusions: In this disease model of metabolic syndrome, vascular structural changes are differentially expressed along the aorta, with pathological features limited to the abdominal rather than the thoracic aorta. These structural abnormalities may underlie the elevated blood pressure seen in this model and potential progression to hypertensive cardiovascular disease.

Tensile properties of Ti–48Al–2Cr–2Nb alloy having similarly oriented lamellae with fine lamellar spacing facilitated by suction casting

Ti–48Al–2Cr–2Nb (at. pct) billet was prepared by suction casting into a cold steel mould, and its microstructures and mechanical properties at room and elevated temperatures were investigated. The billet featured lamellar microstructure with refined colony sizes, fine interlamellar spacing, and lamellar interfaces nearly parallel to the mould surface with a scatter angle within 30°. Benefitting from this microstructure, the billet showed excellent mechanical properties at temperatures up to 850 °C, with yield strength of 629 ± 29 MPa at ambient temperature, 549 ± 14 MPa at 650 °C, 565 ± 17 MPa at 700 °C, 475 ± 6 MPa at 800 °C and 413 ± 9 MPa at 850 °C, comparable to that of the third-generation TiAl alloys like TNM but much superior to that of most reported cast Ti–48Al–2Cr–2Nb alloys. The total fracture elongation at room temperature and 700 °C were (1.8 ± 0.2) % and (15.9 ± 3.5) %, respectively. Although the fracture at 700 °C occurred in a brittle mode, the tensile samples possessed ductile tensile elongation.

Microstructure control and mechanical properties of directionally solidified large size TiAl alloy by electromagnetic confinement

Ti–48Al–2Nb–2Cr alloys with a diameter of 30 mm were prepared by electromagnetic confinement directional solidification with Ti–43Al–3Si seed under different pulling rates. The macro/microstructure evolution and mechanical properties of the directionally solidified Ti–48Al–2Nb–2Cr alloys were investigated. With increasing pulling rates, the grain sizes of the directionally solidified alloys increase to the maximum at the pulling rate of 15 μm/s and then decrease. During the process of directional solidification, the primary phase of the alloy transforms from the α phase into β phase with the increase of pulling rates. At the pulling rate of 5 μm/s, the equiaxed grains with fully lamellar microstructure are formed, and some B2 phases and massive γ phases are found at the grain boundary. The well aligned α2/γ lamellar orientation is obtained at the pulling rate of 15 μm/s, while the inclined lamellar orientation is obtained when the pulling rate increases to 20 μm/s. The interlamellar spacing (λ) decreases with increasing pulling rate (V) according to the relationship λ=6966V−0.563 and r2=0.986. For the DS samples, the nanoindentation hardness of the lamellae and the interlamellar spacing satisfy the relationship of HN=53.83d−0.309 and r22=0.96. The room-temperature tensile strength of directionally solidified alloy reaches the maximum value at the pulling rate of 15 μm/s. The fracture changes from interlamellar to translamellar mode with increasing pulling rate. The synergistic effect of nanotwins and dislocations contributes to the relatively high room-temperature tensile strength and elongation during the deformation.

Rapid Gas Transport from Block-Copolymer Templated Nanoporous Carbon Films

Porous carbon films, attributed to their superior thermal and chemical robustness, are attractive for a number of applications. In the context of molecular separation, a major focus has been on films where the effective pore diameter is lower than 1 nm, e.g., carbon molecular sieves. Only a handful of reports are available on carbon films hosting 2–3 nm size pore channels where gas transport mainly takes place by Knudsen diffusion in contrast to activated transport. Recently, we reported nanoporous carbon (NPC) films, by the pyrolysis of phase-separated block-copolymer/turanose films, as a gas-permeable mechanical reinforcement for crack-free synthesis of single-layer graphene membranes. However, a dedicated study on the nanostructure and transport properties of the standalone NPC film has been missing. Herein, we show that the NPC film has a perforated lamellar (PL) nanostructure where molecular transport is limited by an interlamellar spacing of ∼2 nm. The unique PL nanostructure of the NPC film originates from its precursor, i.e., a block-copolymer stabilized by hydrogen bonding with a carbohydrate additive, where the latter also acts as the main carbon-forming agent. This nanostructure is highly sensitive to the carbohydrate/block-copolymer ratio and gives way to a lacey structure below a ratio of 2:1. The transport of gases through the interlamellar spacing takes place predominantly in the Knudsen regime, determined by their molecular mass. Attributed to a thickness of 100 nm, the film yields extremely rapid gas transport with a H2 permeance over two million gas permeation units (GPU) and H2/CO2 selectivity over 4.5 in a temperature range of 25–300 °C. These properties make the NPC film a promising membrane support and a good choice for the mechanical reinforcement for high-permeance two-dimensional membranes for gas separation.

The Precipitation of Niobium Carbide and Its Influence on the Structure of HT250 for Automobile Wheel Hubs

Improving the strength of grey cast iron wheel hubs will improve the safety of automobiles and have a great significance for energy saving and environmental protection. This paper systematically compares the calculation results of Python-based precipitation calculation and JmatPro software simulation with experiments. The results show that with a low mass fraction of niobium (0.098%) cuboid Niobium Carbide (NbC) precipitates do not form in the liquid phase; however, an elongated NbC niobium-rich phase may form during the solidification process and in the solid phase. However, cuboid NbC precipitates can be precipitated from the liquid phase when the niobium mass fraction is higher (0.27%, 0.46%). These results indicate that with the increasing niobium content the amount, particle size, and initial precipitation temperature of niobium carbide precipitated in the matrix structure will increase. According to the observation and statistical analysis of the microstructure, it is found that tensile strength will be improved with an increase in niobium content due to the refinement of the graphite and pearlite interlamellar spacing. In this paper, adding less than 0.32% of Nb to grey cast iron is recommended, considering the comprehensive cost and the effect of niobium in the material structure.

Construction of lamellar morphology by side‐chain crystalline comb‐like polymers for gas barrier

AbstractA comb‐like polymer containing crystallized alkyl side chains and the intermolecular hydrogen bonds between the linking groups was fabricated by grafting long‐chain fatty amine onto poly(styrene‐co‐acrylic acid)n (P(S‐AA)n, wherein “n” denoted AA feed ratio). The chemical structures and crystallization behaviors of the comb‐like polymer P(S‐AA)n‐g(p) (wherein “p” denoted the number of side‐chain carbon atoms) were analyzed by Fourier transform infrared, gel permeation chromatography, X‐ray photoelectron spectroscopy, and X‐ray diffractometer, differential scanning calorimetry, atomic force microscopy, respectively. It was found that the lamellar morphology could be generated by controlling the grafting density and side chain length of P(S‐AA)n‐g(p). Moreover, it was identified that the hydrogen bonds between amide groups could enhance the crystallinity and then adjust the interlamellar spacing of lamellar phase. As a result, P(S‐AA)70‐g(18) with the highest degree of crystallinity and closely packed lamellar morphology showed a good gas‐barrier performance, and the nitrogen permeability reached 1.78 × 10−14 cm3·cm/cm2·s·Pa. Furthermore, the permeation switch of the obtained comb‐like polymer could reach 500 times traversing the melting point.

Highly Enhancing Electrical, Thermal, and Mechanical Properties of Polypropylene/Graphite Intercalation Compound Composites by In Situ Expansion during Melt Mixing.

Polypropylene/graphite intercalation compound (PP/GIC) composites are prepared via melt mixing at three different temperatures (180, 200, and 220 °C). The dispersion of GICs in the composites is clearly improved due to the increased interlamellar spacing caused by in situ expansion of GICs at higher temperatures, which facilitates the intercalation of PP molecular chains into the GIC galleries. As a result, the PP/GIC composite with 10 wt% GICs prepared at 220 °C (PG220) presents a dielectric constant of about 1.3 × 108 at 103 Hz, which is about six orders higher than that of the composite prepared at 180 °C (PG180). Moreover, the thermal conductivity of the PG220 sample (0.63 Wm−1K−1) is 61.5% higher than that of the PG180 sample. The well-dispersed GICs accelerates the crystallization of PP by increasing the nucleation point and enhances the thermal stability of the composites. The PG220 sample shows a Young’s modulus that is about 21.2% higher than that of the PG180 samples. The results provide an efficient approach for fabricating polymer/GIC composites without complex exfoliation and dispersion processes.

Effect of Interlamellar Spacing on the Low Cycle Fatigue Behavior of a Fully Pearlitic Steel

Effect of Interlamellar Spacing on the Low Cycle Fatigue Behavior of a Fully Pearlitic Steel

Microstructure evolution and mechanical properties of directionally solidified large size Ti-47Al-5Nb-0.18C-0.3Si alloy by electromagnetic confinement

Newly designed Ti-47Al-5Nb-0.18C-0.3Si alloys were directionally solidified by electromagnetic confinement with seed method at the pulling rate of 5–20 µm/s. The macro/microstructure evolution, fracture toughness and high temperature tensile property of the alloy were investigated in detail. The results indicate that the large size single crystals with aligned lamellar microstructure are obtained at the pulling rate of 10 µm/s and 15 µm/s, however, when the pulling rate is lower than 10 µm/s or higher than 15 µm/s, the equiaxed crystals and the divergent columnar crystals are presented instead of the single crystals. Solidification process and macro/microstructure evolution are expressed by schematic, and they display the primary α phase solidification characteristic at the pulling rate of 10–20 µm/s. It is found that the interlamellar spacing gradually decreases with the increase of pulling rate, and the relationship between them can be described as d=14174V−0.83. The single crystal with aligned lamellar microstructure at 10 µm/s possesses the better fracture toughness and high temperature tensile properties. Finally, toughening mechanism and strengthening mechanism are analyzed and discussed.

Study of the dielectric heating of graphite oxide and its effect on the microwave‐assisted synthesis of Nylon‐6/graphite oxide polymeric hybrid nanocomposites

AbstractThe present research focuses on the study of the microwave dielectric heating (DH) of graphite oxide (GrO) during the synthesis of Nylon‐6/GrO hybrid polymeric nanocomposites (HPNCs) employing different microwave input powers and two GrO morphologies. In this regard, we evaluated GrO powder (GrOP) with dimensions ranging from nanometers to microns and GrO films (GrOF) with millimeter lengths and micron thicknesses. Both morphologies show the same oxidation degree and concentration of functional groups. However, they differ in the number of stacked graphene oxide sheets, thus modify their surface area. The results indicated that the morphology of GrO plays a determining role in its DH behavior in the microwave‐assisted polymerization (MAP). On one hand, GrOF contains a high concentration of graphene sheets that induce both an increase in DH and the formation of hot spots. In addition, GrOF has a greater attractive force between its sheets, since its interlamellar space is smaller than 8.4 Å, which makes its exfoliation more difficult. The aforementioned effects significantly reduce the exfoliation and hybridization of GrOF. On the other hand, the larger interlamellar spacing in GrOP weakens the attractive forces compared to GrOF. The lower concentration of graphene oxide lamellae prevents the formation of hot spots, and homogeneously dissipates DH in the reaction medium, maximizing its exfoliation and hybridization. In addition, its behavior presents a defined trend concerning time. These results highlight the importance of considering the GrO morphology in the synthesis of HPNCs as it globally affects the MAPs process, as well as GrO reduction, exfoliation, and hybridization.