Distinct Microstructures Research Articles

Effect of Build Height on Microstructure and Mechanical Properties of Hollow Tubes Fabricated Using Arc-DED Process

The current research effort employed the arc based directed energy deposition (DED) method to create high aspect ratio hollow tubes. The wire feed speed and travel speed of 1.5 m/min and 60 cm/min were chosen for final fabrication with an internal diameter and height of around 6 mm and 120 mm respectively. The properties were assessed in three different regions divided on the basis of build height designated as top, middle and bottom. The findings indicate a significant variation in mechanical properties caused by the presence of distinct microstructures. The superior mechanical properties were achieved in the bottom region, attributed to the grain refinement because of high cooling rate. The grain coarsening contradicts the highest hardness achieved in the top samples owing to the occurrence of brittle M/A islands in the microstructure. Additionally, the M/A islands transform into carbides inside the middle sample because of the elevated tempering temperature circumstances.

Exploring the Effects of Open-Air Cooling on the Formation of Microstructure in Cast A356 Aluminum Alloy

The lightweight composition, non-magnetic nature, and machinability of aluminum alloy A356 make it an important material in many industries due to its significant mechanical properties such as strength, ductility, fatigue resistance, and castability. Aluminium alloy forms an oxide layer when exposed to air. The microstructure of this alloy plays a critical role in determining its mechanical behavior. This study utilized aluminum alloy A356, composed of 92.05% aluminum, 7% silicon, 0.35% magnesium, 0.20% copper, 0.10% manganese, and 0.10% zinc. This alloy exhibits extremely high corrosion resistance, similar to stainless steel, with a melting point of 650°C. The study examines multi- component (mainly Al with Si) A356 containing small amounts of Mg, Cu, Mn, and Zn for their complex microstructural behavior. It includes observations using techniques such as optical microscopy and X-ray diffraction (XRD). This research was carried out to investigate different areas of the same metal’s microstructure and to discover the influence of cooling rates during the solidification process. The findings revealed that there are dissimilarities between the central parts and outer areas, as well as similarities between the two side portions. Also, this study highlights processing conditions’ impact on the material response while looking at heat transfer rate effects during solid-state transformation. The findings of this study highlight the presence of distinct microstructures (dendritic and equiaxed structures) across different sections of the cast Aluminum alloy A356. These findings contribute to a better understanding of the microstructure-property relationship of Aluminum alloy A356, assisting in improvising design and manufacturing processes for enhanced performance.

Predicting Liquid Organic Hydrogen Carrier Saturation In Dehydrogenation Cell Gas Diffusion Layers For Hydrogen Storage

Dehydrogenating methylcyclohexane (MCH) as a liquid organic hydrogen carrier offers a promising method for producing stored hydrogen. However, the transport properties of the gas diffusion layers (GDLs) in dehydrogenation cells (D‐cells) have not yet been optimized for high reactant saturation at the GDL‐catalyst layer (CL) interface, which is crucial for increasing hydrogen production. We apply pore network modeling (PNM) to quantify the anisotropic transport properties and local saturation of MCH in GDLs with distinct microstructures. We demonstrate that GDLs with larger mean pore diameters and lower tortuosity exhibit higher MCH permeability and diffusivity. Moreover, a high porosity at the GDL‐CL interface increases MCH saturation (from 0.05 to 0.11), highlighting the impact of local GDL porosity on MCH supply to the catalyst. The results of the invasion percolation simulation revealed that smaller pore sizes led to a longer MCH transport pathway to the GDL‐CL interface, thereby reducing MCH saturation at this interface (by more than twofold), which hinders reactant availability for hydrogen production. Therefore, we recommend a GDL that combines large pores for efficient MCH flow and small pores close to the CL for liquid retention to enhance MCH utilization in the anode of D‐cell, particularly at high current densities.

Influence of Annealing Treatment on the Microstructure and Mechanical Properties of Cold-Sprayed CoCrFeNiMn High Entropy Alloy

AbstractIn this study, we developed a ~ 2 mm thick deposit of CoCrFeNiMn high entropy alloy (HEA) from cold spray. After cold-spraying, annealing at 600, 800 and 1000 °C for 5 hrs was conducted to improve and consolidate the microstructure. The influence of the annealing treatment on the microstructure, hardness and tensile strength of the HEA deposit was studied. The results showed that annealing treatment increased the fraction of metallurgical bonded areas due to diffusion, which resulted in enhanced mechanical performances of the deposit. The examined fractured surfaces of the tensile test samples revealed that the annealing treatment changed the failure behavior of the as-sprayed deposit from mostly particle-particle interface failure to void coalescence (ductile failure). Interestingly, a distinct microstructure was observed for the deposited annealed at 600 °C; a partially recrystallized microstructure with a small volume fraction of Cr-rich phase formed along grain boundaries, whereas fully recrystallized microstructure at higher two temperatures. The strengthening effect of partial recrystallisation, with a small volume fraction of the Cr-rich phase led to a greater reduced modulus and tensile strength (~196.7 GPa and 51.7 MPa) of the deposit annealed at 600 °C when compared with that annealed at 800 °C (~182.5 GPa and 43.6 MPa). It is believed that the small volume fraction of the Cr-rich phase partly constrained the deformation of the surrounding FCC HEA matrix during mechanical loading, leading to better mechanical properties as compared to the deposit annealed at 800 °C.

Effect of heat treatment on the microstructure of additive manufactured Ni-based hardfacing alloy deposits on stainless steel

Ni based (NiCrFeSiBC) hardfacing alloy was deposited on 304 L SS build plate by laser rapid manufacturing (LRM) process. As-deposited specimen showed nearly a precipitate free zone at the interface, grain boundary (GB) precipitation in stainless steel up to 10 µm, thin dilution layer (∼60 µm) followed by formation of zones with distinct microstructure, microhardness and microchemistry in the deposit. To investigate the effect of thermal exposure on the interface microstructure, deposits were heat treated in the temperature range of 823-1123 K for 5-100 h. Up to 923 K, structure of the LRM deposits resembled that of as-deposited specimen. A planar interface region devoid of precipitates was present even after thermal exposure up to 923 K. With further increase in the temperature, formation of CrB precipitates with globular morphology was observed along the deposit/build plate interface with simultaneous increase in hardness. Thermal exposures beyond 923 K promoted coarsening of M7C3 and Cr2B precipitates. Diffusion of carbon and boron from the deposit to the build plate promoted the grain boundary precipitation of chromium carbides up to a maximum distance of ∼1000 µm for the highest temperature of 1123 K.

Nanoscale phase transformation in SiC wafer by spatiotemporal tailored ultrafast laser pulses for multiple optical data encryption

Color center has shown great potential in optical data encryption due to its tunable optical performance. In this work, precise and controllable implantation of color centers within 4H-SiC wafers has been demonstrated by spatiotemporal tailored ultrafast laser irradiation. Distinct microstructures via micro-ablation, micro-cracking and internal phase transformation can be achieved by precisely regulating the spatial energy input in SiC wafer. The orientation of generated microstructures can be accurately controlled by tuning the laser polarization directions. Those color centers can be further customized by varying the defocusing distances and pulse durations. Wherein, nanoscale amorphous carbon layer with thickness ~ 100 nm was achieved by ultrafast laser induced internal phase transformation, which was ascribed to an enhanced near-field optical effect. Due to the thin-film interference, various colors can display from pink to light-green in those laser modified samples with different carbon nanolayer depths. With the highly flexible and precise modification in SiC crystal, multiple colors can therefore be implanted to encode optical information at small scale, allowing high density and complex information storage. This represents a significant advance in controlled phase transformation for nanoscale color centers fabrication, which is promising in multiple optical data encryption.

Replication of Leaf Surface Structures on Flat Phosphor-Converted LEDs for Enhanced Angular Color Uniformity.

We explored the use of biomimetic structures, including those that mimic leaf structures, to enhance the angular color uniformity of flat phosphor-converted light-emitting diodes (pcLEDs). The distinct microstructures found on natural leaf surfaces, such as micro-scale bumps, ridges, and hierarchical patterns, have inspired the design of artificial microstructures that can improve light extraction, scattering, and overall optical performance in LED applications. The effects of these leaf surface microstructures on the phosphor layer of flat pcLEDs were evaluated. An imprinting technique was employed to directly replicate the surface morphology structures from fresh plant leaves. The results indicated that this method provided excellent scattering capability and reduced the disparity in light output between blue and yellow light emissions from flat pcLEDs at various angles. Subsequently, uniform correlated color temperature in the flat pcLEDs was achieved, reducing the yellow ring effect. Furthermore, the availability of diverse wrinkle and surface patterns from a wide range of natural prototypes could reduce design costs compared with traditional mold fabrication, making the method suitable for application in mass production.

Controllability of optical, electrical, and magnetic properties of synthesized Cd-doped MgFe2O4 nanostructure

This study explores the synthesis of cadmium-magnesium co-doped magnesium ferrite (Mg1+xCdxFe2–2xO4, 0.00 ≤ x ≤ 0.30, Δx = 0.05) via a citric acid-assisted sol-gel auto-combustion method. X-ray diffraction (XRD) analysis revealed crystal structure changes due to Cd and Mg co-doping, with the 0.25 Cd sample showing the smallest crystallite size and highest lattice strain. High-resolution transmission electron microscopy (HRTEM) confirmed the nanostructure and largest surface area for this sample. Diffuse reflectance spectra, analyzed using the Kubelka-Munk relation, indicated that the 0.25 Cd sample had the lowest energy gap (2.08 eV), supported by band position calculations. Electrical conductivity and charge transport mechanisms were examined at various temperatures. Magnetization studies showed reduced saturation magnetization at x = 0.25, ascribed to cation distribution changes and spin canting, with coercivity and anisotropy decreasing with higher Cd content. Overall, the 0.25 Cd sample exhibited optimized optical, electrical, and magnetic properties due to its distinct microstructure.

Broadband Response Diaphragm Materials for Human Acoustics Engineering.

High-performance fiber-reinforced composite materials demonstrate great potential for manufacturing diaphragms in human-engineered acoustic loudspeakers. However, the notable scarcity of high-quality fibers and the uncontrollable nature of the diaphragm structure limit the production of high-quality sound that conforms to human hearing. In this study, a novel composite diaphragm material is devloped by integrating the swelling carboxymethyl cellulose microfiber (CMF) with the hot-melted sheath-core fiber (SCF) based on the "interpenetrating polymeric network" ("IPN") strategy. Simulation methods and Flory-Huggins theory are applied to explain the mechanism of fiber-structure-property interaction in composite diaphragm materials. Owing to the distinct microstructure, this bio-based diaphragm material shows superior mechanical characteristics, including low density (≈0.92gcm- 3), high tensile strength (≈235MPa), and high modulus (≈9.73GPa). Moreover, the loudspeaker mounted with bio-based diaphragm material exhibits enhanced sensitivity (≈82.6dB) and stable performance across a broad frequency spectrum. This study not only elucidates the multiphysics working principles of loudspeakers but also establishes a crucial connection between the physical properties of diaphragms and loudspeaker performance. It opens up new avenues for the design of high-performance bio-based loudspeaker diaphragms in high-fidelity (Hi-Fi) acoustic devices.

High-intensity ultrasound modification of techno-functional and structural properties of white finger millet protein fractions.

In this study, albumin, globulin, and glutelin were extracted from white finger millet, and their amino acid content, functional and structural properties were investigated. The protein concentration of albumin, globulin, and glutelin were 76.01%, 74.32%, and 69.55%, respectively. The results showed that all the fractions had a significant amount of essential amino acids. Aqueous protein dispersions (10%, w/v) were treated for 12min at different ultrasound power levels (100, 200, and 300W). The solubility, emulsifying, and foaming properties of albumin and glutelin were significantly (p<0.05) improved after ultrasound treatment (20kHz) which indicates that ultrasound could unfold protein aggregates. A decrease in particle size, increase in surface hydrophobicity, and zeta potential correlated with improved functional properties. Ultrasound treatment reduced the size of all proteins except for fractions at 300W and also sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a significant change in the molecular weight of albumin and glutelin at 300W. Scanning electron microscopy of treated protein fraction showed distinctive microstructure with irregular structure compared to untreated protein fraction. Although Fourier transform infrared spectroscopy spectra of proteins were similar after ultrasonication, a partial increase in the intensity of the Amide A band was observed. In conclusion, the ultrasound-treated protein fraction can be used as a high-value plant-based emulsifier.

Probing rapid solidification pathways in refractory complex concentrated alloys via multimodal synchrotron X-ray imaging and melt pool-scale simulation

AbstractRefractory complex concentrated alloys (RCCAs) show potential as the next-generation structural materials due to their superior strength in extreme environments. However, RCCAs processed by metal additive manufacturing (AM) typically suffer from process-related challenges surrounding laser material interaction defects and microstructure control. Multimodal in situ techniques (synchrotron X-ray imaging and diffraction and infrared imaging) and melt pool-level simulations were employed to understand rapid solidification pathways in two representative RCCAs: (i) multi-phase BCC + HCP Ti0.4Zr0.4Nb0.1Ta0.1 and (ii) single-phase BCC Ti0.486V0.375Cr0.111Ta0.028. As expected, laser material interaction defects followed similar systematic trends in process parameter space for both alloys. Additionally, both alloys formed a single-phase (BCC) microstructure after rapid solidification processing. However, significant differences in microstructure selection between these alloys were discovered, where Ti0.4Zr0.4Nb0.1Ta0.1 showed a mixture of equiaxed and columnar grains, while Ti0.486V0.375Cr0.111Ta0.028 was dominated by columnar growth. These behaviors were well described by the influence of undercooling effects on columnar-to-equiaxed transition (CET). Distinct microstructure formation in each alloy was verified through CET predictions via analytical melt pool simulations, which showed a ~ 5 × increase degrees in undercooling for Ti0.4Zr0.4Nb0.1Ta0.1 compared to Ti0.486V0.375Cr0.111Ta0.028. Overall, these results show that microstructure control based on modulating the freezing range must be balanced with process considerations which resist defect formation, such as solidification crack formation in RCCAs. Graphical abstract

Molten Metal Jetting for Repairing Aluminum Components

Molten metal jetting (MMJ) is an additive manufacturing (AM) method where droplets of molten metal are used to build parts. Like most AM technologies, MMJ is typically used to build stand-alone parts rather than add onto existing parts. However, the droplet-wise deposition method of MMJ is inherently compatible with the ability to build on existing parts. Here, we utilize MMJ to “repair” machined damage on cast aluminum parts. A commercial MMJ system was used to fill in varied but defined groove geometries to find optimal shapes amenable to repair with MMJ. Subsequently, grooves were cut into tensile specimens and back-filled (repaired) using MMJ. Tensile tests indicate that MMJ repair restores significant strength to samples despite the distinct microstructure and void structures present in the repaired section. Repaired samples demonstrated tensile strengths ∼72% of the as-received material, compared to UTS of ∼33% for damaged samples. These results indicate that MMJ is a viable method to repair parts where other repair methods may be impractical.

Exploring the hardness-independent wear behavior of typical wear-resistant materials under dynamic and static conditions

In this study, three types of wear-resistant materials including high-chromium cast iron (HCCI), medium-chromium cast steel (MCCS), and low-chromium cast steel (LCCS), with similar macroscopic hardness but distinct microstructures and impact toughness have been prepared. The wear behavior of these three materials under different loads were investigated by impact wear experiments under dynamic load and three-body wear experiments under static load. The results revealed that the almost fully martensitised MCCS had the least mass loss under low dynamic impact load wear conditions. The brittleness associated with large carbides intensified with increasing impact load, culminating in a significant reduction in the impact wear resistance of HCCI. The residual austenite rapidly transformed into martensite, thereby effectively improving the wear resistance of the LCCS. Comparatively, the experimental steels were all characterized by fatigue wear of the abrasive on the material surface under static wear conditions at low loads and showed similar wear resistance. Conversely, the large carbides demonstrated superior wear resistance under conditions of high static load, and HCCI had the best wear resistance.

Fluorinated Polyimides incorporated with heterogeneous ZrO2@KNbO3 as multiple carrier transport barriers for Ultra-High energy storage

Advanced electronic devices and electrical power systems require high capacitor energy storage, fast charge–discharge speed and high temperature stability. Inorganic and organic nanocomposite film can achieve this great goal, but the major obstacle is the easy failure of breakdown in harsh environments. Here, we report a seires of inorganic–organic composite films prepared by blending a novel core–shell heterogeneous ZrO2@KNbO3 with fluorinated polyimide (FPI). The ZrO2@KNbO3 forms a distinctive sandwich-like microstructure, which delivers the p-n-p heterojunction interfaces. Multiple energy barriers, arisen at the interfaces, block the charge carrier transport. As a result, the 0.3 ZrO2@KN/FPI nanocomposite film achieves ultrahigh energy densities of 11.62 J cm−3 and 7.9 J cm−3 under electric fields of 665.6 MV m−1 and 550 MV m−1 at 25 °C and 150 °C, respectively, giving rise to a concurrent enhancement in breakdown strength and electrical displacement. Additionally, the 0.3 ZrO2@KN/FPI composite film exhibits superior charge–discharge cycling stability, enduring up to 100,000 cycles. This research provides a cutting-edge perspective to regulate the charge transport path, especially to inhibit charge transport at the interfaces, demonstrating a great potential for high-temperature dielectric capacitor applications.

Synthesis of nano cubic microstructure LiNi0.8Co0.1Mn0.1O2 cathode materials via rapid precipitation assisted with hydrothermal treatment

In this work, a modified Ni-rich cathode material LiNi0.8Co0.1Mn0.1O2 with a unique nano cubic microstructure is successfully synthesized via a rapid precipitation assisted with hydrothermal treatment. The formation of this distinctive microstructure is attributed to the homogeneous rapid precipitation in microreactor, which predominantly generates uniform crystal nuclei. The as-prepared material with nano-/microstructure shows superior initial reversible capacity (205.3 mAh·g−1 at 2.7–4.3 V) and rate capability (163.9 mAh·g−1 at 5 C). Additionally, it maintains a high capacity (188.2 mAh·g−1) with a retention of 87.2 % at 1 C after 200 cycles, demonstrating outstanding cycling stability. Our work presents a straightforward and efficient approach for producing nano-cubic microstructure layered cathode materials.

In situ Rb–Sr geochronology of slickensides reveals reactivation of cratonic margins post-Gondwana assembly

Assessing the time-strain evolution of orogenic structures is a crucial but difficult task, especially for upper-crust structures where the deformation conditions are often below the closing temperature of the main geochronometers. Conventional Rb–Sr and total fusion 40Ar/39Ar techniques are insufficient to spatially-resolve distinct microstructures, such as inherited and recrystallized micas associated with fault zones developed under low to medium-temperature conditions. Here we present in situ Rb–Sr geochronology of fine-grained micas from fault-related rocks of the São Francisco Craton margin, in the Southern Espinhaço Range (SE Brazil), to investigate the timing and effects of fault reactivation at the dawn of Gondwana assembly. Fine-grained muscovite and biotite from slickensides yield Rb–Sr isochron ages spanning 500–450 Ma associated to thrust faults reactivation. This tectonic reactivation is coeval with brittle-ductile deformation of marbles in the footwall of the main regional thrust zones. These novel mica Rb–Sr ages indicate that thrust reactivation was 30–80 Ma younger than the last regional metamorphic event related to collisional deformation in the Araçuaí Orogen, coinciding with the timing of post-collisional magmatism and a fluid flow event in the cratonic margin. We envisage that fault reactivation in the São Francisco Craton margin might be associated with thermal post–orogenic relaxation due to gravitational collapse of the Araçuaí Orogen, with gravity-driven mass transport from the orogenic core causing compressive reactivation in the external fold-thrust-belt. These new results indicate that the Brasiliano thrust fronts remained active throughout the main interval of biogeochemical development in the Ediacaran–Cambrian transition post-Gondwana assembly.

Investigation of kinetics of passive layer formation on various microstructures in thermo-mechanically treated steel in simulated concrete pore solution

Carbon steel bars are critical in steel-reinforced concrete structures, and their corrosion can lead to significant deterioration. This research explored the passive layer formation on different carbon steel microstructures using a high throughput approach. Thermomechanically treated steel bars with three distinct microstructures, i.e., martensite in the outer layer, bainite in the middle, and pearlite in the center, were vertically cut and immersed in the simulated concrete pore solution. Scanning electrochemical microscopy was employed to study the formation of the passive layer, the kinetics of the passivation, and the effective rate constant of the species inside the solution on each microstructure. Results showed that the formation of the passive layer is a time-dependent process, and passivation was influenced by the local microstructure. Martensite demonstrated superior passivation behavior compared to pearlite and bainite.

Enhancing mechanical performance of Ti2ZrNbHfVAlx refractory high-entropy alloys through laves phase

Refractory high-entropy alloys (RHEAs) have attracted significant interest because of their exceptional mechanical characteristics. This study examines the mechanical characteristics, microstructure and strengthening mechanism of Ti2ZrNbHfVAlx alloys (x = 0, 0.2, 0.4, 0.6, 0.8, 1, and 1.2). The results demonstrate that the introduction of Al causes a transformation in the phase structure of the alloys, resulting in the BCC phase and the Laves phase, characterized by a distinctive dendritic microstructure. The compressive yield strength is positively correlated with the rising Al content, while also resulting in a noticeable decrease in ductility due to the presence of the Laves phase. One of the alloys, the compressive yield strength of Ti2ZrNbHfVAl1.2 RHEA is as high as 1789.94 MPa, the compressive strain is 10.60 %, and the specific yield strength (SYS) of 269.67 kPa m3 kg−1. Moreover, the Vickers hardness exhibits a rise from 317.29 to 533.73 HV. The high compressive yield strength mostly originates from solid solution and the second phase strengthening. The current investigation not only offers a resolution for attaining a harmonious combination of strength and ductility but also gives a valuable understanding of the advancement of RHEAs with exceptional mechanical characteristics.

Characteristic deformation microstructure evolution and deformation mechanisms in face-centered cubic high/medium entropy alloys

Face-centered cubic (FCC) high/medium entropy alloys (HEAs/MEAs), novel multi-principal element alloys, are known to exhibit exceptional mechanical properties at room temperature; however, the origin is still elusive. Here, we report the deformation microstructure evolutions in a tensile-deformed Co20Cr40Ni40 representative MEA and Co60Ni40 alloy, a conventional binary alloy for comparison. These FCC alloys have high/low friction stresses, fundamental resistance to dislocation glide in solid solutions, respectively, and share similar other material properties, including stacking fault energy. The Co20Cr40Ni40 MEA exhibited higher yield strength and work-hardening ability than in the Co60Ni40 alloy. Deformation microstructures in the Co60Ni40 alloy were marked by the presence of coarse dislocation cells (DCs) regardless of grain orientation and a few deformation twins (DTs) in grains with the tensile axis (TA) near 〈1 1 1〉. In contrast, the MEA developed three distinct deformation microstructures depending on grain orientations: fine DCs in grains with the TA near 〈1 0 0〉, planar dislocation structure (PDS) in grains with other orientations, and a high density of DTs along with PDS in grains oriented 〈1 1 1〉. Three-dimensional electron tomography revealed that PDS in the MEA confined dislocations within specific {1 1 1} planes, indicating suppression of cross-slip of screw dislocations and dynamic recovery. In-situ X-ray diffraction during tensile deformation showed a higher dislocation density in the MEA than in the Co60Ni40 alloy. These findings demonstrate that FCC HEAs/MEAs with high friction stresses naturally develop unique deformation microstructures which is beneficial for realizing superior mechanical properties compared to conventional materials.

Evolution of Graded Surface Microstructure and Property of Ti6Al4V Threads Processed by Surface Rolling

The surface rolling process is important for the forming property of titanium alloy bolts. This study systematically investigated the evolution of the surface microstructure and property of Ti6Al4V threads induced by surface rolling processes with different feeding times. Gradient surface microstructure and property, as characterized by the depth-dependent variations of refined and deformed grains and hardness, were revealed. A comparative analysis of the microstructure and property of the topmost and subsurface layers in different characteristic areas (root, flank, and crest) of the thread was specifically carried out. The surface microstructure and properties are highly heterogeneous in different areas of the rolled thread. Meanwhile, a gradient microstructure and hardness along the depth from the surface was revealed in the surface layer. Our results showed that the highly heterogeneous surface microstructure and property can be attributed to the close correlation between the different stress/strain levels at different depths from the surface and the different deformation mechanisms in the characteristic surface areas of the thread. The present study has indicated that the distinctive microstructure and property in the different characteristic areas of the rolled thread should be featured by those of surface layers at different depths.