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Due to the long-term cold and heat cycle of gray cast iron parts, thermal fatigue phenomena, such as cracks, locally occur during the service process, resulting in the scrapping of the entire parts. If these defects are surface treated, it will help save energy, reduce emissions, and promote the development of the circular economy. In this study, the Ni60 + Mo coating was prepared on gray cast iron by plasma cladding. The microhardness, microstructure, constituents, thermal fatigue properties, and corrosion wear performance of the cladding layer were analyzed by the microhardness tester, scanning electron microscopy, x-ray diffraction, and thermal fatigue test. The results show that the Ni60 + Mo coating can effectively inhibit the crack propagation and improve the thermal fatigue performance of the cladding layer. Meanwhile, the addition of the Mo element can enhance the diffusion degree of alloying elements in the cladding layer, improve the microstructure uniform, reduce segregation, and promote the formation of equiaxed grain in the cladding layer. With the increase of the Mo element, the average hardness of the plasma cladding layer gradually increases, the fatigue cracks growth rate decreases, the matrix hardness decay value slowly decreases, and the simple wear and corrosion wear properties all decrease. The Ni60-4.5wt.% Mo coating has the best performance. [ABSTRACT FROM AUTHOR]

Cold-rolled plates of metastable austenitic stainless steel (SS) 301LN are the main materials for manufacturing lightweight railway passenger cars, where non-penetration laser welding is used to assemble weld-free sidewalls to improve corrosion resistance and joint strength. Since fast solidified austenitic SSs are susceptible to thermal cracking, microstructure evolutions of laser welded 301LN and AISI 304 were compared and simulated thermal analysis and composition-partitioned detection were carried out. The results showed that both laser welds of 301LN and AISI 304 presented microstructures solidified by mixed modes. Most areas of the 301LN weld showed microstructures solidified with primary δ-ferrite, while the weld root showed a microstructure solidified with primary γ-austenite due to the faster-rate cooling. Most areas of the AISI 304 weld showed microstructures solidified with primary γ-austenite, while the last solidified top central area presented a microstructure solidified with primary δ-ferrite due to the higher local temperature and slower-rate cooling. In addition, the concentration of nickel content caused by macro-segregation led to the 301LN weld center solidify as primary γ-austenite. The microstructure indicated that the laser weld bead of 301LN had higher thermal cracking resistance than that of AISI 304. [ABSTRACT FROM AUTHOR]

Cu matrix composites have received increased attention in a wide industrial area because of their excellent mechanical properties and good electrical and thermal conductivity. However, the addition of general ceramic reinforcements often leads to a marked reduction in electrical conductivity for Cu matrix composites. In this study, the ZrB2-reinforced Cu composites have been developed to overcome this drawback since these metal borides possess relatively high electrical conductivity. The 5 wt.% ZrB2/Cu composites were prepared using hot-pressed sintering techniques at varying temperatures from 760 to 920°C. The influence of sintering temperature on the microstructure, relative density, and mechanical and electrical properties was examined. The results of the SEM observation show that ZrB2 particles are seamlessly integrated into the Cu matrix for all ZrB2/Cu composites. The average grain size of the Cu matrix increases from 360 to 980 nm with the increase of the sintering temperature. The increase in sintering temperature also leads to the surface porosity decrease from 1.4 to 0.4%. The relative density and electric conductivity of the composites increase at the same time as the sintering temperature increases. However, microhardness increases and decreases, with a maximum value of 92 HV0.2 achieved at 840°C. The elastic modulus and nanohardness maps determined from the nanoindentation indicate that the reinforced ZrB2 particles demonstrate the highest values for elastic modulus (340–500 GPa) and nanohardness (30–48 GPa). At the same time, the Cu matrix possesses a modulus of 100–200 GPa and nanohardness of about 10 GPa. TEM observation confirmed that the sintering temperature exhibits little influence on the interface reaction between ZrB2 and Cu. Both sharp interface and interface with amorphous transition layer are observed. The variation of microhardness is mainly due to the strengthening of grain refinement and to the mismatch of the thermal expansion coefficients. The above results can provide further insights into the deeper understanding of the role of sintering temperature during hot-pressed sintering. [ABSTRACT FROM AUTHOR]

AA6060 aluminum alloy was subjected to severe plastic deformation through equal-channel angular pressing (ECAP) up to 8 passes via route BC. ECAPed samples isochronally annealed for 1 hour at a temperature range of 150-450 °C. The microstructure and texture of the studied material were evaluated by electron backscatter diffraction, and the microhardness was characterized by Vickers microhardness testing. It was found that shearing texture is typically enhanced after ECAP processing. Grain size and grain growth kinetics were also studied. ECAP led to a substantial rise in hardness, with stability following 4 passes. Microstructures and material properties were relatively stable up to annealing temperatures of 150 °C. Some sub-micrometer grains were kept in the 8 passes sample to annealing temperatures of 300 °C. Annealing at elevated temperature resulted in a reduction in hardness leading to a rise in grain size and a decrease in dislocation density. After annealing temperature up to 450 °C, the texture index reveals a tendency to the texture weakening and randomization. The activation energy required for the grain growth of the AA6060 alloy was exceptionally low above 300 °C. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization (DRX) behaviors and their transformation process during hot deformation with various Zener–Hollomon (Z) values were investigated in nuclear grade 316H stainless steel, and the factors influencing DRX transformation, especially adiabatic heating, were evaluated in depth. During hot deformation, with the increase of the Z value, the degree of flow softening (DFS) showed a tendency to decrease first and then increase gradually. The analysis of the microstructure revealed that at low Z value (not exceeding 3.9 × 1019 s–1) deformation conditions, DRX was massively activated and the recrystallization mechanism had a transition from continuous DRX (CDRX) to discontinuous DRX (DDRX) with the increasing Z values, leading to the transition of homogeneous grains to heterogeneous grains. Furthermore, with the reactivation of DRX at high Z value deformation conditions, the discontinuous DRX becomes the primary recrystallization mode. Adiabatic heating plays an important role in facilitating the reactivation of DRX and flow softening during hot deformation with low temperature or high strain rate (high Z values, above 6.1 × 1021 s–1). [ABSTRACT FROM AUTHOR]

Incipient melting of homogenized Al–4.5Cu–1.5 Mg–0.1Fe (wt%) alloy, which refers to the intermetallics basically eliminated after homogenization except Al7Cu2Fe phase, has been found under 590 °C. Abnormal phenomenon of the direct formation of a large number of fine dispersed particles and rapid dissolution of Cu- and Fe-rich phases has been observed during the 590 °C annealing process. The gradual gathering of the Cu and Mg solute in Al matrix as liquid phase since the temperature is much higher than its liquidus has been found to be the main reason for such solid-solution incipient melting. This work should provide some guidance for the homogenization process design of Al alloys. [ABSTRACT FROM AUTHOR]

The problem of preparation high-quality graphene has puzzled researchers in the past years. Here we report a novel method to synthesize D peak-free graphene (DPFG) comprising an ordered array of carbon atoms, which can obviously reduce graphene defects. In our investigations, sodium dodecyl benzene sulfonate (SDBS) solution was applied to specially treat nickel foil substrate, which increased nucleation sites for graphene growth and promoted the ordering of carbon atoms around SDBS so as to reduce the defects of graphene. The methodology involves the transformation of the formation of carbon atoms precipitation using dehydrogenation reaction and select coupling. There is a significant interaction between the SDBS and the nickel foil interface, which not only improves structural stability and electrical conductivity but also accelerates the growth of DPFG. Consequently, a hexacyclic-ring system formed due to molecular recombination, based on what further dehydrogenation occurred under full control by temperature. It was easy for those hexacyclic-ring systems to induce nucleation points and promote graphene growth, which caused carbon atoms to regularly grow around the hexacyclic-ring system, and thus reduces obviously the defects of graphene. Our work demonstrated a possible way to design and fabricate DPFG, as well as the applicability of the DPFG in electrochemical application. [ABSTRACT FROM AUTHOR]

Purpose: Multivariate analysis of T2-weighted signal, diffusion ADC, and DKI parameters and tractography were used to differentiate chronic non-specific low back pain (CLBP) patients and asymptomatic controls (AC).Methods: A total of 30 patients with CLBP and 23 AC underwent diffusion kurtosis imaging (DKI) of lumbar spine with a 3T MRI scanner to get the ADC values and seven parameters of DKI in the nucleus pulposus (NP) of the intervertebral disc. The tractography and the tract-related parameters as other parameters were also generated to indicate the intactness of annulus fibrosus (AF). T2-grades of the discs were also quantified based on an eight-grade degeneration grading system. ADC and T2-grades were compared with DKI parameters for the differentiation of CLBP and AC groups.Results: There was no difference in the T2 grades, ADC value, and multiple parameters in DKI of NP between CLBP and AC groups (P > 0.05). The average FA values in NP in AC group were found significantly higher than in the CLBP group (P < 0.05). The scores for the intactness of AF of the intervertebral discs were significantly different in CLBP and AC groups, with 90% of sensitivity and 70% specificity (P < 0.05). Additionally, there were significantly differences in the length and volume values of the AF in CLBP and AC groups (P < 0.05).Conclusion: DKI is a good noninvasive method, and it might help to differentiate CLBP from AC. Particularly, the continuation of DKI tractography reflects the presence of annulus fibrosus fissures, an important character in the generation of the low back pain. These slides can be retrieved under Electronic Supplementary Material. [ABSTRACT FROM AUTHOR]

Objective: Our aim was to assess the microstructural changes of intervertebral disc degeneration induced by annulus needle puncture in rats by diffusion kurtosis imaging (DKI).Methods: Eighteen rats (36 discs) were punctured percutaneously at the intervertebral disc between C6/7, C7/8 (C-coccygeal vertebrae) with a 21-gauge needle. The rats were divided into six groups according to the time after the puncture: 3 h, 48 h, 3 days, 7 days, 10 days and 14 days. There were six discs in three rats in the control group. The rats' tail was imaged at 3T MRI with T2-weighted and diffusion-weighted and diffusion kurtosis imaging (DWI)/DKI sequences. The discs were categorized using a five-grade degeneration system based on the T2 images. The height of the discs and the parameters in DWI/DKI were measured and compared between the different time points. The histological images were also obtained from the discs.Results: The histological study revealed that the discs in the rat of the punctured groups were degenerated. The T2 grades of different groups presented an increasing trend from 7 to 10 days after puncture (R2 = 0.9424, P < 0.001), while the DWI/DKI parameters changes were consistent with the histological changes at the different time points and showed significant differences between the different groups (P < 0.05).Conclusions: DKI provides quantitative assessment of the microstructure changes of disc degeneration, and it is a non-invasive method. The DKI multi-parameter analysis is sensitive to discs changes caused by puncture. These slides can be retrieved under Electronic Supplementary Material. [ABSTRACT FROM AUTHOR]

Abstract: Lignocellulose hydrogels (LCGs) with varying lignin content were prepared by the dissolution-regeneration process using N-methylmorpholine-N-oxide solvent system. The varying lignin content in LCGs can lead to different aggregation states due to the hydrophobic association of lignin, with an important impact on the micromorphology and pore structure of hydrogel. The presence of lignin is beneficial for the mechanical improvement of LCGs when lignin content is lower than 6.5%. LCGs with 6.5% lignin exhibits better viscoelasticity (580.0 kPa), compressive modulus (55.0 kPa), and a more homogeneous structure than others. The LCGs with a lignin content of 11.6% exhibit the best adsorption property (86.1 mg g−1 for Pb2+ and 69.3 mg g−1 for Cu2+), which is dominated by chemisorption and multiple diffusion mechanisms. The work provides a feasible route for lignin-containing hydrogel production and develops a method for tailoring micromorphology and the physical properties of the hydrogel by controlling lignin content.Graphical abstract: [ABSTRACT FROM AUTHOR]

In this study, the enhanced surface properties and microstructure evolution of quenched and tempered cold work die steel Cr12MoV, which were induced by ultrasonic surface rolling process combined with deep cryogenic treatment (UDCT), were systematically investigated. The results indicated that UDCT had an advantage over conventional ultrasonic surface rolling process (USRP) in improving surface mechanical properties, including smaller surface roughness and smoother machined surface with less cracks and defects; higher surface microindentation hardness with the value of ~ 890 HV (increased by ~ 6.2% compared with USRP); and lower friction coefficient. Such enhancements in surface properties are mainly attributed to the martensitic transformation of retained austenite, the dispersion strengthening of small secondary carbides and the homogenized carbides distribution during UDCT. [ABSTRACT FROM AUTHOR]

Sol-gel transition properties play a key role in various applications of thermosensitive hydrogels, but conventional methods for studying the sol-gel transition have some limitations. For extensive characterization of the water-polymer interaction and microstructure change during sol-gel transition, we propose a rapid and nondestructive method based on monitoring water mobility through low field NMR (LF-NMR), and this was applied to chitosan/β-glycerophosphate (CS/GP) hydrogels. The spin-spin relaxation time ( T ) that depicted water mobility was measured by LF-NMR within 90 s. The T component corresponding to water protons trapped in polymer networks ( T ) was very sensitive to sol-gel transition. A remarkable decrease of T value indicated obvious variations of water mobility when CS/GP was heated, and a turning point was observed on the T -time curve. The gel point associated with this turning point could be easily determined by fitting the T -time curves to a bilinear regression model, and the results showed good accuracy and repeatability owing to the nondestructive nature of LF-NMR. Variations in water components and microstructure of CS/GP caused by water migration after solidification were also analyzed by monitoring dynamic changes of T . This rapid, nondestructive method provides a powerful tool for studying the sol-gel transition of hydrogels. [ABSTRACT FROM AUTHOR]

Effects of the normalizing treatment on microstructural evolution, mechanical properties, and impact fracture behavior of 20MnV low alloy cryogenic as-rolled steel were evaluated. The results indicate that grain boundary carbide and acicular ferrite of the as-rolled steel were eliminated and a large amount of nanoscale VC precipitates were observed after 860 °C normalizing treatment. The as-normalized steel had lower strength, higher elongation, and impact absorbed energy than as-rolled steel. The optimal comprehensive mechanical property, especially the superior cryogenic toughness with impact absorbed energy values at −20 and −50 °C were 62 and 40 J, respectively, was obtained at 860 °C. The as-rolled steel contained shearing crack and necking crack simultaneously, while 860 °C as-normalized steel only contained deflecting necking crack, indicating the significant improvement of the toughness. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy, transmission electron microscopy, tensile test, exfoliation corrosion test, and slow strain rate tensile test were applied to investigate the properties and microstructure of Al-Zn-Mg-Cu alloy processed by final thermomechanical treatment, retrogression reaging, and novel thermomechanical treatment (a combination of retrogression reaging with cold or warm rolling). The results indicate that in comparison with conventional heat treatment, the novel thermomechanical treatment reduces the stress corrosion susceptibility. A good combination of mechanical properties, stress corrosion resistance, and exfoliation corrosion resistance can be obtained by combining retrogression reaging with warm rolling. The mechanism of the novel thermomechanical treatment is the synergistic effect of composite microstructure such as grain morphology, dislocation substructures, as well as the morphology and distribution of primary phases and precipitations. [ABSTRACT FROM AUTHOR]

In the paper, the effect of niobium addition on the microstructure, mechanical properties and wear resistance of high chromium cast iron has been studied. The results show that the microstructure of the heattreated alloys is composed of M7C3 and M23C6 types primary carbide, eutectic carbide, secondary carbide and a matrix of martensite and retained austenite. NbC particles appear both inside and on the edge of the primary carbides. The hardness of the studied alloys maintains around 66 HRC, not significantly affected by the Nb content within the selected range of 0.48%-0.74%. The impact toughness of the alloys increases with increasing niobium content. The wear resistance of the specimens presents little variation in spite of the increase of Nb content under a light load of 40 N. However, when heavier loads of 70 and 100 N are applied, the wear resistance increases with increasing Nb content. [ABSTRACT FROM AUTHOR]

This paper studied the microstructures and dielectric properties of PZT coatings prepared by supersonic plasma spraying. Samples of the PZT coatings were evaluated by various techniques. The phases and microstructures of the coatings were investigated by XRD, SEM, and TEM, respectively. The results showed that the coatings deposited on steel substrate had a dense microstructure, and there was no phase transformation during spraying. Additionally, the Curie temperature of the PZT coatings was about 370 °C by the investigation of dielectric constant. [ABSTRACT FROM AUTHOR]

Here, we report the atomic-scale microstructural characterization and dielectric properties of crystalline cubic pyrochlore BiMgNbO (BMN) nanoparticles with mean size of 70 nm, which were synthesized by sol-gel method. The crystallinity, phase formation, morphology, and surface microstructure of the BMN nanoparticles were characterized by X-ray diffraction (XRD), Raman spectra, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), respectively. The phase evolution of the BMN nanoparticles investigated by XRD patterns showed that uniform cubic pyrochlore BMN nanoparticles were obtained after calcination at temperature of 800 °C, and their structural information was revealed by Raman spectrum. TEM images demonstrated that the BMN nanoparticles had a spherical morphology with an average particle size of 70 nm, and their crystalline nature was revealed by HRTEM images. In addition, HRTEM images also demonstrate a terrace-ledge-kink (TLK) surface structure at the edges of rough BMN nanoparticles, where the terrace was on the (100) plane, and the ledge on the (001) plane. The formation of such a TLK surface structure can be well explained by a theory of periodic bond chains. Due to the surface structural reconstruction in the BMN nanoparticles, the formation of a tetragonal structure in a rough BMN nanoparticle was also revealed by HRTEM image. The BMN nanoparticles exhibited dielectric constants of 50 at 100 kHz and 30 at 1 MHz, and the dielectric loss of 0.19 at 1 MHz. [ABSTRACT FROM AUTHOR]

In this study, a high Cr cast iron surface composite material reinforced with WC-Co particles 2-6 mm in size was prepared using a pressureless sand mold infiltration casting technique. The composition, microstructure and hardness were determined by means of energy dispersive spectrometry (EDS), electron probe microanalysis (EPMA), scanning electron microscope (SEM) and Rockwell hardness measurements. It is determined that the obtained composite layer is about 15 mm thick with a WC-Co particle volumetric fraction of ~38%. During solidification, interface reaction takes place between WC-Co particles and high chromium cast iron. Melting and dissolving of prefabricated particles are also found, suggesting that local Co melting and diffusion play an important role in promoting interface metallurgical bonding. The composite layer is composed of ferrite and a series of carbides, such as (Cr, W, Fe)23C6, WC, W2C, M6C and M12C. The inhomogeneous hardness in the obtained composite material shows a gradient decrease from the particle reinforced metal matrix composite layer to the matrix layer. The maximum hardness of 86.3 HRA (69.5 HRC) is obtained on the particle reinforced surface, strongly indicating that the composite can be used as wear resistant material. [ABSTRACT FROM AUTHOR]

ZrO nanocrystallites based charge trap memory cells by incorporating a (ZrO)(SiO) film as a charge trapping layer and amorphous AlO as tunneling and blocking layer were prepared and investigated. The precipitation reaction in charge trapping layer forming ZrO nanocrystallites during rapid thermal annealing was investigated by transmission electron microscopy. The density and size of ZrO nanocrystallites are the critical factors for controlling the charge storage characteristics. The ZrO nanocrystallites based memory cells after postannealing at 800 C for 60 s exhibit the best electrical characteristics and a low charge loss ∼5 % after 10 write/erase cycles operation. [ABSTRACT FROM AUTHOR]

The effects of trace silver and magnesium additions on the microstructure and mechanical properties of the Al−Cu−Li alloys were investigated. The experimental results indicate, that the effect of combined additions of Ag and Mg is the most obvious, the next is that of individual addition of Mg, and that of individual addition of Ag is the least. The addition of Ag and Mg in Al−Cu−Li alloy accelerates the precipitation of T1 and results in increasing the ageing hardness and strength. Prior cold work significantly improves the tensile strength by enhancing T1 precipitation in all the alloys investigated. [ABSTRACT FROM AUTHOR]

Examines the effect of lithium on the aging characteristics and microstructures of aluminum-copper-magnesium-silver alloys with low copper:magnesium ratio. Alloys preparation by melting and casting under argon atmosphere; Indication that low copper:magnesium ratio aluminum-copper-magnesium alloys containing silver and lithium exhibit promising properties; Implication that the alloy possesses higher tensile properties.

Examines the effect of lithium on the aging characteristics and microstructures of aluminum-copper-magnesium-silver alloys with low copper:magnesium ratio. Alloys preparation by melting and casting under argon atmosphere; Indication that low copper:magnesium ratio aluminum-copper-magnesium alloys containing silver and lithium exhibit promising properties; Implication that the alloy possesses higher tensile properties.

Compositionally graded (Ba1-xSrx)TiO3 (BST) thin films (with 0.0 ? x ? 0.25) were grown by pulsed laser deposition on the (100)MgO single-crystal substrates covered with a conductive La0.5Sr0.5CoO3 (LSCO) layer as a bottom electrode. Their epitaxial growth, dielectric response, and microstructure were characterized. The epitaxial relationships between the BST, LSCO, and MgO can be determined as [001]BST//[001]LSCO//[001]MgO and (100)BST//(100)LSCO//(100)MgO, from the x-ray diffraction (rocking curve, ? scans) and electron-diffraction patterns. Dielectric data showed that the room temperature values of the dielectric constant and dielectric loss of the graded BST films were 630 and 0.017 at 100 kHz, respectively. Cross-sectional transmission electron microscopy (TEM) images reveal that both the BST films and the LSCO bottom electrode grow with a columnar structure, and they have flat interfaces and overall uniform thickness across the entire specimen. Cross-sectional high-resolution TEM images reveal that at the LSCO/MgO(100) interface, an interfacial reaction is not seen, whereas edge-type interfacial dislocations with their extra half-planes residing in the LSCO side are observed with an average interval of 2.20 nm, close to the theoretical value of 2.15 nm. At/near the LSCO/BST interface, the graded BST films grow perfectly and coherently on the LSCO lattice because they have the same type of crystal structure and almost same lattice constants, and no interfacial dislocations are observed. Planar TEM images show that the graded films exhibit granular and/or polyhedral morphologies with an average grain size of 50 nm, and the aligned rectangular-shaped voids were also observed. High-resolution TEM images show that the length sizes of voids vary from 8 to 15 nm, and with width of 5 to 10 nm along the <001> direction in the (100) plane. [ABSTRACT FROM AUTHOR]