Composition Segregation Research Articles

Random photoluminescence emission base-on droplet evaporative segregation of All-inorganic perovskite for All-photonic cryptographic primitive

Segregation is a phenomenon of inhomogeneous distribution of constituent elements during crystallization and could be found in alloy, polymers, colloid, etc. Some researchers have also found component segregation in perovskite crystals. Until now, the existing research reports are all about the halogen segregation of perovskite at the micro level, while the research about the component segregation of perovskite at the macro level is blank, leaving no relevant application developed. Therefore, we can broaden the PUFs-based application of perovskite crystals by employing the multi-wavelength emission property arising from component macrosegregation. We synthesized perovskite crystal arrays with macroscopic composition segregation in one step by surface-tension-confined evaporative self-assembly. The macrosegregation in perovskite crystals prepared with different halogen ratios and temperature was surveyed. The photoluminescence spectra of perovskite crystals were investigated. Perovskite crystals with composition segregation could generate physically unclonable cryptographic primitives, which were made by a simple and random process and difficult to replicate. According to the number of peaks in the spectrum, we converted the optical response into quaternary cryptographic keys, and demonstrated the randomness and stability of the system. This study excavated the application prospect of macroscopic component segregation perovskite in all-photonic cryptographic primitives.

Microstructure and mechanical properties in TLP joint of FeCoNiTiAl alloy and IC10 superalloy using Mn-Ni-Cr filler

A filler metal of Mn-Ni-Cr was used to transient liquid phase (TLP) bonding high-entropy alloy (HEA) of FeCoNiTiAl and Ni3Al base IC10 superalloy for 10 min ~ 120 min at 1150 °C and a pressure of 2 MPa. There was no diffusion affected zone (DAZ) existed in the bonded zone as the filler material Mn-Ni-Cr contained no conventional melting-point depressants (MDPs) of Si/B. Hence, the TLP joint was composed of two isothermally solidified zones (ISZs) and an athermally solidified zone (ASZ). The ISZ beside IC10 consisted of strip Ni(Al, Mn) phases, resulted from the diffusion of Al atoms, and only γ-(Ni, Mn) phases formed in another ISZ adjacent to HEA base metal (BM). Moreover, sluggish diffusion of HEA can prevent the BM from dissolving and formed a straight bond line consisting of “(Hf, Ta)C + Al0.89Mn1.1” compound in the interface between HEA and bonded zone. Furthermore, increase of bonding time can lead to enrichment of Al in the bonded zone and induce composition segregation during solidification. A compound of “Ni(Al, Mn) + Ni3Ta” formed in ASZ of joint bonded for 30 min ~ 120 min. Hardness results revealed that formations of Ni(Al, Mn) phases and the compounds in ASZ can cause the alternant hardness distribution of valley and peak across the joint and lead to the generation of stress concentration. Therefore, the maximum shear strength, 269.9 MPa, was achieved in the joint dwelled for a period of 10 min.

Microstructural Study of Arc Beads in Aluminum Alloy Wires with an Overcurrent Fault.

To clarify the understanding and analysis of arc molten marks in electrical faults of aluminum alloy wires, this paper simulates overcurrent faults of aluminum alloy wires at currents of 128 A–224 A and uses thermogravimetry-differential scanning calorimetry (TG-DSC), optical microscope (OM), scanning electron microscope (SEM) and X-ray energy spectroscopy (EDS) to characterize the effects of current on the microstructure of arc beads. The results show that there are small and large amounts of Al-Si and Al-Fe binary phases in the metallographic structure of the aluminum alloy wires at the rated current, the grains are fine, and there are no significant grain boundaries. After an overcurrent fault occurs in the wires, a high-temperature arc causes the second phase in the aluminum alloy to disappear, a cellular dendritic metallographic structure appears, the grain boundaries become more well-defined, and composition segregation occurs at the grain boundaries. Using Image-Pro-Plus software to quantify the grain characteristics, the average grain size is found to gradually decrease as the current increases. In addition, by comparing and analyzing the characteristics of arc beads in aluminum wires and aluminum alloy wires under the same conditions, alloying elements are found to have a refining effect on the grain boundaries, and there are coarse precipitates at the grain boundaries in the aluminum wire arc beads.

Investigation into the magnetic properties of CoFeNiCr y Cu x alloys

The search for cheap, corrosion-resistant, thermally-mechanically stable functional magnetic materials, including soft magnetic and magneto-caloric materials has led to research focused on high entropy alloys (HEAs). Previous research shows that alloying elements with negative enthalpies of mixing can facilitate a second-order phase transition. On the other side of the spectrum, compositional segregation cause by positive enthalpy of mixing alloying additions (such as Cu) may also be used to tune magnetic properties. This paper studies the structural, magnetic and magneto-caloric effect of the FCC alloys CoFeNiCr y Cu x (x = 0.0, 0.5, 1.0 and 1.5, y = 0.0, 0.8 and 1.0) to tune these properties with Cu and Cr alloying. Scanning electron microscopy of the compositions show nanoparticles forming within the grains as the Cu concentration increases. Cr addition to CoFeNiCu1.0 has a larger effect on the magnetic and magneto-caloric properties compared to the Cu addition to CoFeNiCr1.0. The addition of Cu (x = 0.5) to CoFeNiCr1.0 improved both the saturation magnetisation and Curie temperature; addition of Cr (y = 1.0) to CoFeNiCu1.0 decreased the Curie temperature by 900 K. All alloys were determined to have a second-order phase transition around their Curie temperature. The refrigerant capacity at 2 T was found to be similar to existing HEAs, although the Curie temperatures were lower than room temperature. Based on this data the CoFeNiCr0.8Cu composition was fabricated to increase the Curie temperature towards 300 K to explore these HEAs as new candidates for room temperature magneto-caloric applications. The fabricated composition showed Curie temperature, saturation magnetisation, and refrigerant capacity increasing with the small reduction in Cr content.

Wide-Band-Gap Mixed-Halide 3D Perovskites: Electronic Structure and Halide Segregation Investigation.

Mixed-halide organolead perovskites ( ) are of great interest for both single-junction and tandem solar cells because of their wide band gap. In this study, we investigate the family of mixed iodide/bromide (I/Br) and bromide/chloride (Br/Cl) perovskites, revealing the strong influence of halide substitution on electronic properties, morphology, film composition, and phase segregation. A qualitative blue shift with the I → Br → Cl series was observed, with the resulting optical absorption ranging from 420 to 800 nm covering nearly the entire visible region. The ionization potential increases from ≈6.0 to ≈7.0 eV as the halide composition changes from I to Br. However, with Cl components, the valence band position shows little variation, while the conduction band minimum shifts to a lower value with increasing Cl concentration. By collecting XPS spectra as a function of the sputtering depth, we observed halide segregation in both I/Br and Br/Cl mixed-halide perovskite films, where the large halide ion (I in the I/Br mix or Br in the Br/Cl mix) is preferentially found on the surface of the film and the smaller halide ion (Br in the I/Br mix or Cl in the Br/Cl mix) accumulates at the bottom of the film. These differences in the band structure, electronic properties, morphology, and film composition impacted the device performance: a decreased short-circuit current density and increased open-circuit voltage were observed with the I → Br → Cl series. This study highlights the role of halides in the band structure and phase segregation in mixed-halide perovskite solar cells and provides a foundational framework for future optoelectronic applications of these materials.

Interfacial characteristics and residual welding stress distribution of K4750 and Hastelloy X dissimilar superalloys joints

Gas tungsten arc welding (GTAW) method was employed to join a newly developed cast superalloy K4750 with Hastelloy X by using K4750 and Hastelloy X filler metals (FMs), respectively. Thereby we obtained two kinds of interfaces namely K4750 base metal (BM) and Hastelloy X FM, and K4750 FM and Hastelloy X BM. The elemental distribution, interfacial characteristics, and the residual welding stress of the dissimilar joints were investigated by electron probe micro analyzer (EPMA), electron backscattered diffraction (EBSD), and section technique, respectively. The results showed that the elemental distribution across both interfaces were varied significantly. And the composition segregation regions were identified in both interfaces but the segregation extent was different. Epitaxial growth was clearly observed in both interfaces. The distribution of the residual welding stress across the joint exhibited that the highest tension stress area in both as-welded joints was located at the joint heat affected zone (HAZ). The residual welding stress in the joint with Hastelloy X FM was significantly relieved through post weld heat treatment (PWHT).

In-situ fabrication of Ti2AlNb-based alloy through double-wire arc additive manufacturing

For the reason of high temperature strength, high oxidation resistance and low density, Ti2AlNb-based alloy is expected to replace nickel-based alloy in the range of working temperature 600–800 °C and become a new generation of high-temperature structural alloys in the aerospace industry. However, Ti2AlNb-based alloys have great high-temperature deformation resistance and high brittleness, which greatly restricts its preparation and processing using traditional technology. In this research, an innovation method named double-wire arc additive manufacturing technology was adopted to in-situ manufacture Ti-22Al-24Nb (at%) alloy, and the TiNb and pure Al wire with designed feeding speed were taken as raw materials. The deposited component was investigated systematically. Results show that the composition error between the average testing value and designed value are under 1.1%, but there are also existing local segregation of composition and microstructure. The segregation phenomenon further deteriorates its mechanical properties, which means the ultimate tensile properties and elongation under room temperature and high temperature (650 °C) are 504 ± 38.59 MPa, 0.41 ± 0.03% and 375 ± 32.60 MPa, 0.76 ± 0.05% respectively on average. At the same time, the prepared alloy exhibits fully lamellar structure and XRD results show that the basic composition phases B2, O and α2 of the Ti2AlNb-based alloy successfully appeared. The in-situ manufacturing method demonstrated in this work is expected to significantly promote the wider application of AM due to its low cost advantage and high flexibility.

Effects on microstructural refinement of mechanical properties in steel‑copper joints laser welded with alternating magnetic field augmentation

In this research project, pure copper and stainless steel were joined using laser beam welding in the presence of an alternating magnetic field. The microstructure, element distribution and mechanical properties of the welded joints were then analyzed using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and other methods. We determined that the microstructure in the fusion zone transformed in the alternating magnetic field improved laser welding process from bulky banded and spherical structures to fine blocky and granular structures. Grain refinement and inhibition of composition segregation were achieved with the addition of electromagnetic force generated by alternating current, reducing susceptibility to solidification cracking. During the metallurgical interaction, diffusion of solute atoms decreased the microstructure gradient significantly, reducing thermal stress and improving the mechanical properties of the welded joints. The emergence of an increased number of shear dimples in the fracture confirmed improvement in ductility. A physical model is proposed to validate the strengthening and toughening mechanisms of the laser welded joints augmented by alternating magnetic force.

Unravelling diet composition and niche segregation of colonial waterbirds in a Mediterranean wetland using stable isotopes

Rice fields and waterbirds are an example of a synergy that can occur between agriculture and conservation. This connection is especially relevant during the farming period, when nesting waterbirds need to obtain resources to cover their energy requirements and those of their chicks in rice fields. However, new farming techniques may potentially put fulfilling this role at risk. Studies on how species use rice fields to feed during this critical period are essential to understand waterbird population dynamics and to optimize conservation measures. At present, several species of colonial birds in l’Albufera de València (Spain) that depend on trophic resources available in rice fields have decling populations and decreases in productivity. We therefore assessed trophic niche segregation in the diet of chicks of a waterbird community composed of seven species through stable isotope analyses of carbon (δ13C) and nitrogen (δ15N) obtained from chick blood and tissue samples of potential prey. According to trophic niche widths, chicks of Black‐headed GullChroicocephalus ridibundusand Gull‐billed TernGelochelidon niloticashowed a similar diet, although Gull‐billed Tern had a major trophic specialization. The Western Cattle EgretBubulcus ibisfed its chicks in a wider range of different habitats, with organisms located at the base of the food chain and with a greater importance of terrestrial prey than other species. Conversely, the Glossy IbisPlegadis falcinellushad a more differentiated diet, mostly in freshwater habitats and mainly consuming odonates. Grey HeronArdea cinerea, Little EgretEgretta garzettaand Squacco HeronArdeola ralloidesshowed overlap between their niches, largely explained by the presence and abundance of cyprinid fish and odonates in their diets. Our results suggest a less important role than expected of Red‐swamp CrayfishProcambarus clarkii, and a more important role of odonates despite being a less energy‐rich prey. In conclusion, the diet of generalistic species of waterbirds in this study suggests that their trophic niches can overlap when relative prey abundance is high.

Fabrication of TiAl alloys turbocharger turbine wheel for engines by metal injection molding

The TiAl turbine wheels possess high acceleration responsiveness and low energy consumption due to its low density, high specific strength and excellent oxidation resistance. However, the mechanical properties of the turbine wheels fabricated by conventional casting can't be fully utilized resulted from inherent defects and compositional segregation. Herein, we used a near-net shaping MIM technology to fabricate this alloy and firstly produced a TiAl alloy turbocharger turbine. The rheological properties of feedstocks, microstructure and mechanical properties were systematically studied. Results indicate that the Feedstock F3 has better rheological properties and no powder-binder separation during injecting using numerical simulation. The microstructure is homogenous and fine-grained fully α2/γ lamellar structure with average size of 111.7 μm. The HIPed TiAl alloy displays excellent mechanical properties which are higher than that of the equivalent casting TiAl alloys. This work presents a valuable method for fabricating complex-shaped TiAl alloy turbine wheels.

Transient liquid phase bonding of Ni3Al based superalloy using Mn–Ni–Cr filler

A new 70Mn–25Ni–5Cr (wt. %) filler with no traditional melting-point depressants (MPDs) of Si/B was used for transient liquid phase (TLP) bonding a directionally solidified (DS) superalloy based on Ni3Al intermetallic compound (IMC) at 1150 °C, a pressure of 2 MPa for 10–120 min. Experimental results show that the joint can be divided into 3 zones, isothermally solidified zone (ISZ), athermally solidified zone (ASZ) and diffusion-affected zone (DAZ), which was similar to microstructure of typical TLP joint bonded by Ni based filler. The joint microstructures were mainly composed of γ-Ni, γ′-Ni3(Al, Ta), MC and M23C6 carbides. Besides, in the ISZ, due to the enrichment of Al, which diffused from the base metal (BM), strip-shaped Ni(Mn, Al) phases formed in such region. The ASZ included γ-Ni and compounds of “equiaxed Ni(Mn, Al) + acicular Ni3Ta” owing to the composition segregation during the later stage of solidification. Moreover, as the bonding time increased, the volume fraction of Ni(Mn, Al) and MC carbides decreased owing to homogenization of alloying elements. After bonding for 120 min, sufficient isothermal solidification (IS) of filler can also decrease segregation of Mn/Al in front of the S/L interface and the Ni(Mn, Al)+Ni3Ta compounds were eliminated almost. Thus, the highest tensile strength was 816.9 MPa of the TLP joint of 120 min, which has been equivalent to that of BM (812 MPa). However, due to the existence of a few residual large MC carbides in the joint, which can induce the stress concentration and decreased the ductility of the joints, the highest joint elongation of 4.4% was only about 40% of the BM.

Composition uniformity of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals grown in 〈0 0 1〉 direction

As a typical representative of the second generation of relaxor-PbTiO3 (PT) ferroelectric single crystals, Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals exhibit an improved thermal stability of piezoelectric properties compared with PMN-PT single crystals. The high quality and large-size PIN-PMN-PT single crystals are required for transducers. Composition segregation inevitably exists in relaxor-PT ferroelectric crystals grown by the vertical Bridgman method, resulting in poor uniformity of piezoelectric properties. The single crystal boule grown in 〈001〉 direction have the best composition uniformity. In this work, the composition uniformity of PIN-PMN-PT single crystals grown in 〈001〉 direction was investigated. The PT content varies from 31 mol% to 35 mol% from the bottom to the top of crystal boule. The TR/M−T decreases gradually from 113 °C to 73 °C and TC increases from 155 °C to 184 °C respectively. Optimizing the poling condition, the dielectric and piezoelectric properties of 80% of the single crystal boule can keep consistent.The free dielectric constant ε33T/ε0 and piezoelectric coefficient d33 are 4500–5000 and 1700–1900 pC/N, respectively, showing the improvement of theutilization of crystal boule.

Halide Segregation in Mixed-Halide Perovskites: Influence of A-Site Cations.

Mixed-halide perovskites offer bandgap tunability essential for multijunction solar cells; however, a detrimental halide segregation under light is often observed. Here we combine simultaneous in situ photoluminescence and X-ray diffraction measurements to demonstrate clear differences in compositional and optoelectronic changes associated with halide segregation in MAPb(Br0.5I0.5)3 and FA0.83Cs0.17Pb(Br0.4I0.6)3 films. We report evidence for low-barrier ionic pathways in MAPb(Br0.5I0.5)3, which allow for the rearrangement of halide ions in localized volumes of perovskite without significant compositional changes to the bulk material. In contrast, FA0.83Cs0.17Pb(Br0.4I0.6)3 lacks such low-barrier ionic pathways and is, consequently, more stable against halide segregation. However, under prolonged illumination, it exhibits a considerable ionic rearrangement throughout the bulk material, which may be triggered by an initial demixing of A-site cations, altering the composition of the bulk perovskite and reducing its stability against halide segregation. Our work elucidates links between composition, ionic pathways, and halide segregation, and it facilitates the future engineering of phase-stable mixed-halide perovskites.

Nanostructure and compositional segregation of soft magnetic FeNi\u2010based nanocomposites with multiple nanocrystalline phases

Soft magnetic metal amorphous nanocomposite alloys are produced through rapid solidification and thermal annealing yielding nanocrystals embedded within an amorphous precursor. Similar free energies in Co‐rich and FeNi‐based alloy systems result in multiple nanocrystalline phases being formed during devitrification. Studies of multi‐phase crystallization processes have been reported for Co‐rich alloys but relatively few have investigated FeNi‐based systems. A detailed characterization of compositional partitioning and microstructure of an optimally annealed FeNi‐based MANC (Fe70Ni30)80Nb4Si2B14 alloy is presented through complementary high‐resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). HRTEM demonstrates orientation relationships between FCC and BCC nanocrystals, suggesting heterogeneous nucleation of nanocrystals in the amorphous matrix or a cooperative mechanism of nucleation between BCC and FCC nanocrystallites. APT results show evidence for (i) the segregation of Fe and Ni between nanocrystals of different phases, (ii) B partitioning to the amorphous phase, and (iii) an Nb‐enriched shell surrounding nanocrystals.

Intratracheally instillated diesel PM2.5 significantly altered the structure and composition of indigenous murine gut microbiota

A diverse and large community of gut microbiota reside in the intestinal tract of various organisms and play important roles in metabolism and immune homeostasis of its host. The disorders of microbiota-host interaction have been closely associated with numerous chronic inflammatory and metabolic diseases, including inflammatory bowel disease and type 2 diabetes. The accumulating evidence has shown that fine particulate matter (PM2.5) exposure contributes to the diabetes, atherosclerosis and inflammatory bowel diseases; however, few studies have explored the impact of inhaled diesel PM2.5 on gut microbiota in vivo. In this study, C57BL/6J mice were exposed to diesel PM2.5 for 14 days via intratracheal instillation, and colon tissues and feces were harvested for microbiota analysis. Using high-throughput sequencing technology, we observed that intratracheally instillated diesel PM2.5 significantly altered the gut microbiota diversity and community. At the phylum and genus levels, principal coordinate analysis (PCoA) and principal component analysis (PCA) indicated pronounced segregation of microbiota compositions, which were further confirmed by β diversity analysis. As the most affected phylum, Bacteroidetes was greatly diminished by diesel PM2.5. On the genus level, Escherichia, Parabacteroides, Akkermansia, and Oscillibacter were significantly elevated by diesel PM2.5 exposure. Our findings provided clear evidence that exposure to diesel PM2.5 via intratracheal instillation deteriorated the gastrointestinal (GI) tract and significantly altered the structure and composition of gut microbiota, which might subsequently contribute to the developmental abnormalities of inflammation, immunity and metabolism.

Microstructural and electrochemical characterization of the passive film on a 50-kg hot rolled FeCrNiCoMn high entropy alloy

FeCrNiCoMn high entropy alloy has outstanding mechanical properties at cryogenic temperature, and the related articles surge recently. However, the studies of large-scale FeCrNiCoMn alloys have not yet been reported. This work detailed the microstructure and corrosion behavior associated with the compositional segregation of a 50-kg FeCrNiCoMn in 0.5 M H2SO4 in the form of as-cast, hot-rolled, annealed, and homogenized alloys. Interdendritic segregation was observed in the central and columnar zones of as-cast FeCrNiCoMn, where Mn was the critical element trigging the corrosion. The annealing at 900 °C for 1.5 h effectively improved the general corrosion resistance and passivity of the partially-recrystallized FeCrNiCoMn, whereas the complete homogenizing at 1200 °C for 24 h did not further improve the passivity. The structure of the passive film was characterized using Auger electron spectroscopy (AES), high-resolution transmission electron (HRTEM), and scanning transmission electron microscopy (STEM). The AES results show that the passive film on the Mn-rich and Mn-poor regions had a similar composition. Like 304 L SS, the homogenized FeCrNiCoMn had the passive film enriched of Cr and with Ni enrichment beneath the surface. The passive film on homogenized FeCrNiCoMn was amorphous based on HRTEM and the thickness was estimated to be 1.66 nm by STEM. Finally, the corrosion behavior of the distinct FeCrNiCoMn alloys was discussed in detail based on the effect of casting defects, composition segregation, deformation defects, grain boundaries, and Mn-related oxide/sulfide inclusions.

Gas adsorbate-induced Au atomic segregation and clustering from Cu(Au)

Surface compositional and phase segregation in an alloy can change its functionality, especially for applications where surface structure and chemistry play a vital role. For instance, the surface status of alloy catalysts significantly affects their catalytic performance for both heterogeneous and electrochemical processes. Surface segregation is believed to be driven by the difference in surface energy to reduce the total free energy of the alloy. However, the atomistic processes during the segregation process remain elusive, especially for gas molecule-induced segregation, where both structural and chemical reordering may occur. Herein, we achieved in-situ atomic-scale visualization of the surface segregation behaviors of a solid solution Cu(Au) alloy under the CO gas by an aberration-corrected environmental transmission electron microscope. CO-induced Cu(Au) surface ordering structures largely change the surface chemistry of the alloy. Further gas exposure at elevated temperature could facilitate Au atom diffusion through a specific “atomic channel” structure for dealloying and clustering on the surface. The segregated Au nanoparticles show rich phase and morphological dynamics interacting with the alloy surface, where the gas adsorption also plays an important role. These atomic insights provide direct evidence for the surface segregation and dealloying mechanisms of bimetallic alloys, and highlight the role of gas adsorbate in these surface processes.

The Mechanical Response of Nanoporous Gold and Silver Foams with Varying Composition and Surface Segregation

The mechanical response of an Au-Ag nanoporous foam is studied via molecular dynamics simulations, while segregation effects are captured by a Monte-Carlo simulation scheme. The addition of silver to nanoporous Au structures increases the strength of the foams.Dislocation evolution in alloyed and pure elemental structures is analyzed. We find that the yielding behavior is dependent on surface compositions and the corresponding capillary forces, while elastic behavior is dependent on bulk composition. Trends in the yield response of this material as a function of size and surface composition are effectively predicted with a model that accounts for surface effects.

Nanostructure and compositional segregation of soft magnetic FeNi-based nanocomposites with multiple nanocrystalline phases

Abstract

Electrically Assisted Solid-State Joining of CrMnFeCoNi High-Entropy Alloy

Equiatomic CrMnFeCoNi high-entropy alloy was joined in solid-state by electrically assisted pressure joining (EAPJ). Cracks and compositional segregation were not found in joining zones (JZ). As the applied electric current increased, the microstructure of JZ changed from a deformed and partially recrystallized microstructure to a fully recrystallized one with grain growth. JZ showed sound mechanical properties through the Vickers hardness and uniaxial tension results. EAPJ of high-entropy alloy can overcome the disadvantage of fusion welding.