Nano-sized Phase Research Articles

The Influence of Precipitated Particles on the Grain Size in Cold-Rolled Al-Mn Alloy Foils upon Annealing at 100-550 °C.

The Al-Mn alloy heat exchanger fin production process includes a brazing treatment at s high temperature of 600 °C, in which coarse grains are preferred for their high resistance to deformation at elevated temperatures by decreasing the grain boundary sliding. In this study, Al-1.57Mn-1.57Zn-0.58Si-0.17Fe alloy foils cold rolled by 81.7% (1.1 mm in thickness) and 96.5% (0.21 mm in thickness) were annealed at 100-550 °C for 1 h to investigate their recrystallization behavior, grain sizes, and precipitates by increasing the annealing temperature, using micro-hardness measurement, electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The micro-hardness results showed that the recrystallization finishing temperatures for the two samples were almost the same, 323 ± 2 °C. The EBSD results showed that when the annealing temperature decreased from 550 to 400 °C, the recrystallized grain sizes of the two samples were nearly identical-both increased slightly. Further decreasing the annealing temperature from 400 to 330 °C caused the grain sizes to increase more, with the thinner foil sample having a more significant increase. The SEM and TEM observations showed that the micron-sized primary-phase remained unchanged during the annealing process. The nano-sized secondary phase precipitates formed during the hot-rolling process experienced a coarsening and dissolving process upon annealing. The particle size of the secondary phase increased from 32 nm to 44 nm and the area fraction decreased from 4.2% to 3.8%. The nucleation analysis confirmed that the large primary-phase could act as a nucleation site through particle stimulated nucleation (PSN) mode. The relatively dense secondary phase precipitates with small sizes at lower temperatures could provide higher Zener drag to the grain boundaries, leading to fewer nuclei and thereafter coarser grains. The coarsening of the recrystallized grains in the foils could be implemented through thickness reduction and/or precipitation processes to form densely distributed nano-sized precipitates.

PRODUCTIVE METHODS FOR INCREASING THE EFFICIENCY OF INTERMEDIATE REACTIONS IN THE SYNTHESIS OF FUNCTIONAL CERAMICS

This study focuses on investigating the potential of modified ceramic technology methods for producing composition materials with nano-level heterogeneity, approximating the properties of functional ceramics (FC) obtained through helio-technology. Three different powder synthesis methods were utilized: oxide method, ceramic technology, and sol-gel technology. X-ray diffraction and electron microscopy analyses were employed to compare the microstructure of powders obtained by these methods with samples synthesized using helio-technology. The results revealed that powders obtained through modified ceramic technology methods exhibited a more homogeneous structure and smaller particle size compared to those obtained through helio-technology. Nano-sized, metastable, and amorphous phases formed at the boundaries of such powders are considered responsible for the generation of pulsed infrared radiation. These findings have significant practical implications in various fields that require composition materials with controlled properties and the ability to generate pulsed infrared radiation.

Microstructural design to Al-6Mg-5Gd alloy for the unification of structural and neutron shielding properties

Design of composition and microstructure can effective improve the structural and neutron shielding properties of neutron shielding materials. Based on the shielding standard of 30%B4C/Al, an Al-6Mg-5Gd (wt%) alloy was designed by Shmakov-Yamamoto model and successfully fabricated by Powder Metallurgy-based routines (e.g., powder fabrication, spark plasma sintering and hot extrusion techniques). By the rapid solidification in the atomization process, the submicron cell structures were formed in powders. Due to the difference in the original powder size, the as-sintered alloys had heterogeneous microstructures, leading to the bimodal grain structures of as-extruded alloys. During these processes, the formation of nano-sized τ(C15) (Al4MgGd) phase in combination with its firstly observed transformation behavior showed the great impacts on microstructure evolutions. Therefore, the as-extruded alloy exhibited the superior yield strength (335±7 MPa), ultimate tensile strength (462±5 MPa) and elongation (10.2±0.3%). Through the neutron absorption test, the as-extruded alloy showed the comparable of macroscopic transmission cross section with 30%B4C/Al. In comparison with the available Al-based neutron shielding materials, our report exhibited the best unification of mechanical and functional properties. The underlying mechanisms for synergic strength-ductility behavior were discussed on the nano-sized phase strengthening, α-Al/τ interface modulation, and bimodal grain features. Critically, this work designed and studied a high-performance neutron shielding material, shedding light on the advanced structural-functional integrated materials.

Phonon relaxation effect by regeneration of nano-inclusions in SiGe for ultralow thermal conductivity and enhanced thermoelectric performance

SiGe alloys exhibit high thermoelectric performance at mid to high temperatures, but their wide applications are hindered by intrinsically high thermal conductivity. Here, we report a new strategy for regenerating ultrafine nano phases of CrSi2 and SiO2 with an average grain size of approximate 130 nm by chemical reaction of Si and strong oxidizing CrO3 in a p-type SiGe matrix. Based on the Debye-Callaway calculation, the nano-sized second phase leads to a reduction in phonon relaxation time, thereby lowering the thermal conductivity to an ultralow value of 2.15 W m−1 K−1 at 873 K. The boundaries between the second phases (CrSi2) and the matrix (SiGe) establish potential barriers, allowing carrier filtering and phonon scattering, thus increasing the power factor. Eventually, the sample (CrO3)0.3-Si80Ge20B0.5 reaches a peak ZT of approximately 1.12 at 873 K, with an average ZT of approximately 0.62 from 323 K to 873 K, representing a 55.56% improvement compared with Si80Ge20B0.5. Our method provides a promising approach for enhancing the thermoelectric performance of SiGe.

Effect of aging treatment on microstructure and wear performance of Ni-rich NiTiFe alloy

NiTi-based alloys with high nickel content have been utilized as a novel bearing material because of their exceptional hardness, superior wear resistance and corrosion resistance etc. In this work, microstructure, hardness and wear behavior of (Ni56Ti44)95Fe5 alloy were investigated as a function of aging duration. It is found that with increasing aging duration, Ni4Ti3 phase formed continuously and transformed into Ni3Ti phase in a short time due to the addition of Fe. In this case, the highest hardness (729 HV) and the lowest coefficient of friction (0.611) were obtained in the sample aged at 400 °C for 5 h. The dependence of hardness and wear behavior of (Ni56Ti44)95Fe5 alloy was attributed to the combined effect of Orowan strengthening by nano-sized Ni4Ti3 phase and the soften effect of Ni3Ti phase. The wear behavior of (Ni56Ti44)95Fe5 alloy was governed by the combined mechanism of adhesive wear, abrasive wear and oxidative wear.

Excellent tribocorrosion resistance of additively manufactured Ti-based heterogeneous composite coating via hardening and toughening effects

To improve the tribocorrosion resistance of oil drill pipes used in deep-sea drilling, a Ti-based composite coating was successfully fabricated by laser direct energy deposition technology on the TC4 titanium alloy surface. The microstructure analysis showed that a new heterogeneous structure of multistage strengthening phases (micron-sized TiN phases and nano-sized TiB phases) distributed on the β matrix (soft Cu-rich phases and hard Mo-rich phases) was formed, and the size of β grain was refined to 2 μm with the content of Cu higher than 12 wt.%. The microhardness of the composite coating was increased to more than 700 HV0.2 due to the solution strengthening of Mo elements and the formation of hard TiN phases. At the same time, the fracture toughness of 12Cu composite coating was significantly increased to 8.37 MPa m1/2, which was attributed to the combined effect of grain refining, high-density dislocations in Cu-rich phases, and nanoscale TiB phases. The synergistic enhancement of hardness and toughness of 12Cu composite coating promoted the generation of titano-molybdenum-copper composite oxide film on the worn surface, and the tribocorrosion resistance increased more than 7 times compared with TC4.

Toxicity assessment of nano-sized MAX phases: considerations for safe-by-design approaches

Toxicity of two nano-sized MAX phases, Ti2AlC and Ti3AlC2 were investigated to provide fundamental data for implementing the safe-by-design (SbD) approach.

Study of the Chemical Vapor Deposition of Nano-Sized Carbon Phases on {001} Silicon.

Different nano-sized phases were synthesized using chemical vapor deposition (CVD) processes. The deposition took place on {001} Si substrates at about 1150-1160 °C. The carbon source was thermally decomposed acetone (CH3)2CO in a main gas flow of argon. We performed experiments at two ((CH3)2CO + Ar)/Ar) ratios and observed that two visually distinct types of layers were deposited after a one-hour deposition process. The first layer type, which appears more inhomogeneous, has areas of SiO2 (about 5% of the surface area substrates) beside shiny bright and rough paths, and its Raman spectrum corresponds to diamond-like carbon, was deposited at a (CH3)2CO+Ar)/Ar = 1/5 ratio. The second layer type, deposited at (CH3)2CO + Ar)/Ar = a 1/0 ratio, appears homogeneous and is very dark brown or black in color and its Raman spectrum pointed to defect-rich multilayered graphene. The performed structural studies reveal the presence of diamond and diamond polytypes and seldom SiC nanocrystals, as well as some non-continuously mixed SiC and graphene-like films. The performed molecular dynamics simulations show that there is no possibility of deposition of sp3-hybridized on sp2-hybridized carbon, but there are completely realistic possibilities of deposition of sp2- on sp2- and sp3- on sp3-hybridized carbon under different scenarios.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Al0.6CoCrFeNi High-Entropy Alloy.

The effect of heat treatment on the microstructure and tensile properties of an as-cast Al0.6CoCrFeNi high-entropy alloy (HEA) was investigated in this paper. The results show that the as-cast Al0.6CoCrFeNi HEA presents a typical FCC dendrite morphology with the interdendritic region consisting of BCC/B2 structure and heat treatment can strongly affect the microstructure and mechanical properties of HEA. Microstructure analysis revealed the precipitation of a nano-sized L12 phase in the FCC dendrite and the formation of the FCC and σ phases in the interdendritic region after annealing at 700 °C. The coarse B2 phase was directly precipitated from the FCC dendrite in the 900 °C-annealed sample, with the coexistence of the B2, FCC, and σ phases in the interdendritic region. Then, the interdendritic region converted to a B2 and FCC dual-phase structure caused by the re-decomposition of the σ phase after annealing at 1100 °C. The tensile test results show that the 700 °C-annealed HEA presents the most significant strengthening effect, with increments of corresponding yield strength being about 107%, which can be attributed to the numerous nano-sized L12 precipitates in the FCC dendrite. The mechanical properties of 1100 °C-annealed alloy revert to a level close to that of the as-cast alloy, which can be attributed to the coarsening mechanism of B2 precipitates and the formation of a soft FCC phase in the interdendritic region. The observed variation in mechanical properties during heat treatment follows the traditional trade-off relationship between strength and plasticity.

Interfacial strain driven nucleation and growth of grain boundary phases

Secondary phases precipitation in grain boundaries (GBs) are ubiquitous presence in multicomponent polycrystalline materials, and play a crucial role in determining the materials performances. However, the atomistic formation mechanism remains a matter of conjecture since the GB phase is difficult to well characterize. Here, using a typical Mg-rare-earth binary alloy as the model system, we systematically investigated the precipitation behaviors of nano-sized secondary phases in a partially coherent tilt GB. Atomic-scale observations combined with theoretical calculations show that GB elastic strain minimization drives the segregation of solutes to the interfacial strain zones, and the selective substitution of solutes resulting in the nucleation of face-centered-cubic (FCC) phase from the bi-crystalline hexagonal closed-packed (HCP) lattices. Interphase boundary strain driven solute diffusion plus atomic shuffling can realize the growth of parent phase {11¯00}HCP lattices to the {110}FCC atomic-planes. These findings not only confirm a novel HCP to FCC phase transition pathway, but also provide a mechanistic insight into the nucleation and growth of GB phases.

Microstructure of Nd2Fe17N3 Magnetic Powder Surface With Nano-α-Fe Phases Separated Surface Layer

We investigated the application of Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> magnetic powder with planar magnetic anisotropy to magnetic field amplification materials at several tens of MHz. Consequently, we succeeded in developing a magnetic property with real permeability ~ 8 and imaginary permeability below 0.8 at 100 MHz using a phosphoric acid coating and a simple heat treatment process in air. In this study, microstructural analysis conducted using transmission electron microscopy and X-ray diffraction revealed that the coating layer became thicker, and the Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surface was phase-separated into nano-sized α-Fe phases and Nd-rich phases, either oxide, oxynitride, or nitride. Additionally, the nano-sized α-Fe phases and the nano-sized Nd-rich phases were oriented over a wide area spanning several hundred nanometers. We concluded that these characteristic structures have led to improved properties.

Effect of Sm and Ce content on microstructure and mechanical property of newly developed Mg-Sm-Ce-Mn based alloy

In this work, the effect of Sm and Ce contents on mechanical property of Mg-Sm-Ce-Mn based alloy have been investigated, and it is found that both the strength and ductility increased continuously with the increase of solute contents. In the as-extruded Mg-1.6Sm-0.8Ce-0.4Mn alloy, a high strength-ductility synergy was obtained, with yield strength (YS) of 269 MPa and an elongation (EL) of 21%. The increase of Sm and Ce elements introduces the high density of micro-sized and nano-sized second phases as well as the Sm segregation at grain boundaries, which leads to an increase in the recrystallization fraction, more evident dynamic recrystallized (DRXed) grain refinement, and also the texture weakening. The increased density of nano-phases and the DRXed grains refinement lead to the higher strength, and the decrease in dislocation density and texture weakening contribute to the excellent ductility. The relevant work can shed light on designing other low-cost and high-performance Mg wrought alloys containing the cheap light rare-earth elements.

Hydrogen desorption kinetics of magnesium hydride co-doped with titanium trifluoride and nickelocene

MgH2 is a promising hydrogen storage material and its hydrogen desorption kinetics can be enhanced by introducing catalysts. To deeply understand synergetic effect of multiple phases on hydrogen desorption of MgH2, the formation mechanism of catalytic phases and their effect on hydrogen storage properties were studied in a MgH2 - 5 wt% TiF3 - 15 wt% NiCp2 composite. The experimental results demonstrate that the nano-sized Mg2NiH4, TiH2 and MgF2 phases can be formed in situ after sample preparation and activation. The in situ formed phases provide a synergetic effect on hydrogen absorption and desorption during subsequent cycling, leading to the significant enhancement of hydrogen desorption kinetics and cycle durability. This work provides guidance for the design and preparation of novel Mg-based materials with excellent hydrogen storage properties.

Study of the effect of heat treatment on corrosion property of the AlxCoCrFeNi high-entropy alloys (x = 0.3, 0.7, and 1) prepared by spark plasma sintering

The effect of spark plasma assisted heat treatment (SPHT) on the corrosion property of Al0.3CoCrFeNi, Al0.7CoCrFeNi, and AlCoCrFeNi HEAs is studied in this paper. The Tafel and EIS measurement is adopted to determine how the corrosion resistance varies before and after SPHT. The Al0.3CoCrFeNi and Al0.7CoCrFeNi HEAs show an enhancement in corrosion resistance after SPHT as their corrosion current density (icorr) decreases and polarization resistance. The SPHTed Al0.7CoCrFeNi HEA features the best corrosion resistance as it has the lowest icorr of 7.1 × 10−10 A/cm2 and the highest polarization resistance of 139.89 kΩ·cm2. Nevertheless, SPHT damages the corrosion resistance of the AlCoCrFeNi HEA. The phase transition of FCC-B2 and BCC-FCC is revealed to benefit the corrosion resistance but the precipitation of the σ phase is found to damage corrosion resistance after SPHT. Cr is proven to be the most corrosion-resistant content while Al and Ni contents are easy to be corroded. The different particle size of the transformed phase decides their disparate effects on corrosion resistance as the micro-sized Cr-enriched phase increases the corrosion resistance by effectively covering the corrosion surface but the nano-sized Cr-enriched phase decreases the corrosion resistance by reducing the Cr contents in the neighboring matrix.

Hierarchical crystalline–amorphous nanocomposites with high strength and large deformability enabled by elemental diffusion

Amorphous/nanocrystalline dual-phase structures have recently emerged as an effective way for overcoming the strength–ductility trade-off and breaking the limitation of the reverse Hall–Petch effect. Here, we proposed a new strategy to develop a hierarchical and interconnected amorphous–crystalline nanocomposite arising from the nanoscale elemental interdiffusion and oxygen adsorption behavior during thermal treatment processes. The nanocomposite consisted of a three-dimensional (3D) hierarchical network structure where the crystalline phase (Cr–Co–Ni–Al) was embedded into the Al–O-based amorphous phase network with critical feature sizes encompassing three orders of magnitude (from micrometer to nanometer scale). It can achieve ultrahigh compression yield strength of ∼3.6 GPa with large homogeneous deformation of over 50% strain. The massive interstitial atoms induced lattice distortion and hierarchical amorphous phase boundary contributed to the strength improvement. in situ Uniaxial compression inside a transmission electron microscope (TEM) revealed that the exceptional deformability of the nanocomposites resulted from the homogenous plastic flow of nano-sized amorphous phase and the plastic co-deformation behavior restricted by the nano-architected dual-phase interface. The proposed dual-phase synthesis approach can outperform conventional nanolaminates design strategies in terms of the mechanical properties achievable while providing a pathway to easily tune the microstructure of these nanolaminates.

Effect of Sr on Microstructure and Strengthening Mechanism of Al-4.6Mg Alloy.

The as-cast Al-4.6Mg alloy was subjected to deformation and sensitization-desensitization heat treatment, and then the microstructure and the enhancement mechanism of Sr were investigated by optical microscopy, scanning electron microscopy-energy-dispersive spectroscopy, electron backscatter diffraction, and transmission electron microscopy. The precipitation phases of Al-4.6Mg alloy were mainly β-Al3Mg2, Al6Mn, and Al6(Mn Cr), and the nanoscale precipitation phases were Al3Mn and Al11Mn4. The formation of β-Al3Mg2 was hindered by the addition of 0.1 wt.% Sr. In addition, the precipitate phase Al4Sr and the nano-sized precipitate phase τ-Al38Mg58Sr4 were uniformly distributed in the spherical matrix. The addition of Sr promoted the redissolution of Mg atoms in Al-4.6Mg alloy, increasing the solubility of Mg in the α-Al matrix from 4.7 wt.% to 5.1 wt.%. The microstructure analysis showed that Sr addition inhibited the recovery and recrystallization of the alloy because the Sr element elevated the recrystallization temperature. As a result, the grain deformation was intensified, the grain size was decreased from 6.96 μm to 5.39 μm, the low-angle grain boundaries were increased from 78.7 at % to 84.6 at %, and the high-angle grain boundaries were increased from 21.3 at % to 15.4 at %. Furthermore, the mechanical properties of the alloy were significantly improved, and the plasticity degraded after the addition of the Sr element. The yield strength of the alloy was enhanced mainly through fine grain strengthening, dispersion strengthening, solid solution strengthening, and working hardening. The strengthening mechanisms were analyzed in detail.

Modulation of structure and corrosion behavior of Si-DLC coatings on AZ31 by applying a self-source bias

The Si-DLC coating was fabricated on AZ31 via a dual system consisting of a self-source bias and a meshed plasma immersion deposition, where the incident ion energy can be modulated by the self-source bias. The structure was characterized using field emission scanning electron microscope, transmission electron microscope, Raman spectroscopy, and Fourier transform infrared spectroscopy. The corrosion behavior was evaluated using an electrochemical workstation. The utilization of the bias significantly densifies the coating structure, producing a nano-sized SiC phase and elevating its corrosion resistance. Notably, the −500 V bias coating exhibits superior short-term corrosion resistance. Interestingly, the high-energy ion bombardment produced by the high bias induces carbon diffusion in the coating, leading to the formation of a nano-ceramic TiC interface, which further enhances the corrosion resistance of the Si-DLC coating. Moreover, the increase in bias is accompanied by a decrease in surface porosity, hydrogen content, and sp2/sp3 ratio. In addition, the mechanisms involved in the formation of the TiC nano-interface and the corrosion resistance of the coating are analyzed and explained. A modulated approach to enhance the corrosion resistance of Si-DLC coatings and provide protection against magnesium alloys is achieved by dense structures resulting from high-energy ion bombardment.

Deformation behavior and microstructure evolution induced by nano-sized Al6Mn phase particles in a homogenized Al–6Mg–0.8Mn alloy during hot compression

In the present work, hot compression deformation behavior and microstructure evolution in a homogenized Al–6Mg–0.8Mn alloy with nano-sized Al6Mn phase particles were investigated at the temperature ranging from 300 to 500 °C with tha strain rate of 0.001–1 s−1. The constitutive equation of the Al–6Mg–0.8Mn alloy was established and the average deformation activation energy was calculated to be 167.07 kJ/mol. The flow stress of the alloy decreased with increasing the compression temperature and raised with increasing the strain rate, which was closely associated with the competitive relationship between work hardening and dynamic recovery (DRV). The low compression temperature accelerated the formation of shear bands in the alloy. The low strain rate was beneficial for the generation of low-angle grain boundaries (LAGBs), and the high compression temperature and strain rate promoted dynamic recrystallization (DRX). The interaction between the nano-sized Al6Mn phase particles participating near the initial grain boundaries and mobile dislocations facilitated the generation of LAGBs. Discontinuous DRX through grain boundary bulging mechanisms and continuous DRX with the LAGBs transforming to HAGBs led to the preferred formation of recrystallized grains along the initial large-sized grains. Furthermore, this interaction also resulted in the dissolution of Al6Mn phase particles.

Nano-sized stationary phase packings retained by single-particle frit for microchip liquid chromatography

Modern chromatography is increasingly focused on miniaturization and integration. Compared to conventional liquid chromatography, microfluidic chip liquid chromatography (microchip-LC) has the potential due to its zero-dead volume connection and ease of integration. Nano-sized packings have the potential to significantly enhance separation performance in microchip-LC. However, their application has been hindered by packing difficulties. This study presents a method for packing nano-sized silica particles into a microchannel as the stationary phase. The microchip-LC packed column was prepared by combining the weir and the porous silica single-particle as frit to retain the packing particles. A surface tension-based single-particle picking technique was established to insert porous single-particle frit into glass microchannels. Additionally, we developed a slurry packing method that utilizes air pressure to inject nano-sized packing into the microchannel. Pressure-driven chromatographic separation was performed using this nano-packed column integrated into a glass microchip. The mixture of four PAHs was successfully separated within just 8 min using a 5 mm separation channel length, achieving high theoretical plates (106 plates/m). Overall, these findings demonstrate the potential of utilizing nano-sized packings for enhancing chromatographic performance in microchip systems.

All-polymer organic solar cells with nano-to-micron hierarchical morphology and large light receiving angle

Distributed photovoltaics in living environment harvest the sunlight in different incident angles throughout the day. The development of planer solar cells with large light-receiving angle can reduce the requirements in installation form factor and is therefore urgently required. Here, thin film organic photovoltaics with nano-sized phase separation integrated in micro-sized surface topology is demonstrated as an ideal solution to proposed applications. All-polymer solar cells, by means of a newly developed sequential processing, show large magnitude hierarchical morphology with facilitated exciton-to-carrier conversion. The nano fibrilar donor-acceptor network and micron-scale optical field trapping structure in combination contributes to an efficiency of 19.06% (certified 18.59%), which is the highest value to date for all-polymer solar cells. Furthermore, the micron-sized surface topology also contributes to a large light-receiving angle. A 30% improvement of power gain is achieved for the hierarchical morphology comparing to the flat-morphology devices. These inspiring results show that all-polymer solar cell with hierarchical features are particularly suitable for the commercial applications of distributed photovoltaics due to its low installation requirement.