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Ultrafine grained (UFG) n-C/Al composite bulk was obtained by mechanical milling and hot extrusion with petroleum coke utilized as carbon source. After extrusion, n-C sheets got dispersed and distributed in grain interiors or at grain boundaries. The tensile strength and corresponding thermal conductivity reached 407 ± 3 MPa and 216 ± 1.6 W m−1 K−1.

ABSTRACT Polypharmacy in managing severe tuberculosis patients usually poses a risk of adverse drug reactions. Contezolid is a new oxazolidinone antibiotic showing good in vitro and in vivo activity against Mycobacterium tuberculosis. Contezolid add‐on regimen shows promising efficacy and safety results in managing severe tuberculosis patients complicated with acute thrombocytopenia.

With the rapid development of Mg alloys, deeper understanding to the thermodynamic and diffusional kinetic behavior of intermetallic compounds (IMCs) is important for studying the effect of alloying elements to the microstructure evolution. Specially, a systematic quantitative investigation on the diffusional growth of IMCs is of great necessity. However, the works studying the elemental diffusion behaviors of multiple-element IMCs are rare in magnesium alloy systems. The current work takes the ternary Mg-Al-Zn system as research target, and combines the diffusion couple technique, phase stability diagrams, in-situ observation technique and numerical inverse method to investigate the temperature-dependent kinetic coefficients. The parabolic growth constant (PGC) and interdiffusion coefficients for Mg solid-solution phase and γ-Mg17Al12, β-Mg2Al3, ε-Mg23Al30, MgZn2, Mg2Zn3, τ-Mg32(Zn, Al)49 and ϕ-Mg5Zn2Al2 IMCs in the Mg-Al-Zn alloy system are determined. By comparing the current experimental with calculation results, the rate-controlling factor of the temperature-dependent diffusion growth of ϕ, τ and ε ternary IMCs in the Mg-Al-Zn system is further discussed in detail.

Ultra-fine grained magnesium alloys are usually prepared by severe deformation and medium-low temperature deformation. In this work, it has been found that the binary Mg-1.2Ce alloy with the uniform distributed Mg12Ce precipitates smaller than 3 μm is a good candidate to obtain ultra-fine grains by conventional one-step extrusion at high temperatures. All the three Mg-1.2Ce samples extruded at 300 °C, 350 °C and 400 °C show a bimodal microstructure with high-density dislocations, whose average grain sizes are 1.19 ± 0.92 μm, 1.32 ± 1.30 μm, and 1.44 ± 1.33 μm, respectively. A linear relation of ln(d) = -0.05ln(Z)+1.27 was determined relating the average grain size (d) to the Zener-Hollomon parameter (Z). The alloy extruded at 300 °C exhibits an exceptionally high ultimate tensile strength (UTS) of 412.3 ± 5.3 MPa and yield strength (TYS) of 387.6 ± 3.2 MPa, but a low elongation after fracture (El) of 4.9 ± 0.8 %. With the extrusion temperature increasing, the tensile strength gradually decreases. For the 1.2E-400 sample, the TYS and the UTS drop to 347.2 ± 2.1 MPa and 349.4 ± 2.8 MPa, while the El increases to a more acceptable value of 12.6 ± 1.4 %. The microstructure analysis reveals that Ce atoms segregate along grain boundaries and dislocations in the Mg-1.2Ce alloy, which can limit the gliding of GBs or the slipping and climbing of dislocations. Additionally, dislocations can be pinned by Mg12Ce precipitates, thereby also restricting dislocation and grain boundary mobility. Consequently, the dynamic recrystallization (DRX) process is delayed, leading to the formation of a bimodal microstructure.

Heat-resistant Al alloys used in such as aerospace, transportation fields are attracting more and more attention in recent years. Within Al alloy families, Al–Cu–Mg alloys have shown promising heat resistance properties. This work aims to investigate the influence of Cu/Mg ratio and content on the heat resistance of Al–Cu–Mg alloys, based on alloys of Al–4.5Cu–2.5 Mg (referred to as alloy A), Al–4.0Cu–2.2 Mg (alloy B) and Al–4.5Cu–1.6 Mg (alloy C). The alloys A and B possessed approximate Cu/Mg ratio, and they also exhibited nearly identical hardness retention rate during exposure at 200 °C. After 200 h, the rate is ∼75 %, though alloy A showed higher hardness (105 vs. 102 HBW) due to higher Cu, Mg content. In contrast, alloy C with a higher Cu/Mg ratio was less heat-resistant, with hardness retention rate of ∼70.5 % after 200 h exposure. Nano-sized S′(Al2CuMg) precipitate was main strengthening phase for the three alloys. Also, micron and submicron Al2CuMg particles could be formed with increase of Cu and Mg contents, which contributed a lot to yield strength for T6 heat-treated alloys, but slight contribution after exposure at 200 °C for 200 h. The degradation of mechanical properties during heat exposure can be attributed to the transformation and coarsening of S′ precipitates. In alloys with lower Cu/Mg ratio, there was excess Mg dissolved in Al matrix, which reduced Cu solubility in α-Al, and then slowed diffusion flux of Cu element, thus inhibited coarsening of Al2CuMg phase.

In an effort to clarify the formation mechanism of LPSO structure in Mg-Y-Zn alloy, the chemical environment and structural ordering in liquid Mg-rich Mg-Y-Zn system are investigated with the aid of ab-initio molecular dynamics simulation. In liquid Mg-rich Mg-Y alloys, the strong Mg-Y interaction is determined, which promotes the formation of fivefold symmetric local structure. For Mg-Zn alloys, the weak Mg-Zn interaction results in the fivefold symmetry weakening in the liquid structure. Due to the coexistence of Y and Zn, the strong attractive interaction is introduced in liquid Mg-Y-Zn ternary alloy, and contributes to the clustering of Mg, Y, Zn launched from Zn. What is more, the distribution of local structures becomes closer to that in pure Mg compared with that in binary Mg-Y and Mg-Zn alloys. These results should relate to the origins of the Y/Zn segregation zone and close-packed stacking mode in LPSO structure, which provides a new insight into the formation mechanism of LPSO structure at atomic level.

Morphology and distribution of intermetallic compounds in the heat-affected zone (HAZ) are easily altered during welding thermal cycles, contributing to the softening of the HAZ. Finding solutions to mitigate the softening and enhance the strength of the joint is currently at the forefront of Mg alloy processing and manufacturing. In this work, 0.7 mm thick Ce-containing Mg alloy sheets were successfully joined using fiber laser welding. The microstructure of the joint was observed employing scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Accordingly, the phase compositions in both HAZ and fusion zone (FZ) were determined. Subsequently, the mechanical properties of the joint were evaluated through tensile-shear and hardness tests. The results revealed that the HAZ experienced softening, retaining 76.6% of the strength of the base metal in the tensile-shear test. Interestingly, intermetallics composed of conventional alloying elements within the HAZ transformed into coral-like structures during the welding thermal cycles, whereas the morphology and distribution of intermetallics containing rare-earth (RE) elements barely changed. As a result, the joint exhibited cracks along the boundaries of the coral-like precipitates during tensile loading. In comparison, both intermetallics consisting of conventional elements and those containing RE elements were fragmented into micron-sized fine particles in the FZ, leading to an increase in the strength of the FZ. Ultimately, the mechanisms responsible for the softening of the HAZ and the strengthening of the FZ were elucidated, presenting a promising welding solution for Mg alloys.

Magnesium alloys, as the lightest structural alloys, provide the possibility of solving environmental problems by improving energy efficiency. Developing and maintaining nanocrystalline matrix is a huge challenge, and the key to achieving ultra-high strength. The nanocrystalline Ti/AZ61 composite prepared by hot pressing was annealed, and its microstructural evolution was characterized via SEM, XRD, and TEM, including the changes in magnesium matrix, Ti dispersions, and nano-scale precipitates. The density and mechanical properties of annealed composites were tested and analyzed. After annealing treatment at 623 K for 80 h, the average grain size of nanocrystalline Ti/AZ61 composites was 102 nm. 97% of Ti dispersions were submicron sized, and Ti3Al precipitates remained nanometer-sized. Ti dispersions and Ti3Al precipitates were uniformly distributed in the magnesium matrix. Compared with hot pressed composites, the crack that originated from the prior particle boundary (PPB) was restrained for annealed composites. The improved density and PPB bonding strength of annealed Ti/AZ61 composites had a positive impact on strength and plasticity. After annealing treatment for 40 h, the density increased from ∼2.041 g/cm3 to 2.066 g/cm3. The hardness, yield strength, and FFS were 146 HV, 493 MPa, and 5.6%, respectively, with corresponding increasing rates of 7%, 12%, and 65%, respectively.

The aim of this study was to determine the microstructural evolution, tensile characteristics, and strain-hardening response of AZ31B magnesium alloy welds as influenced by post-weld heat treatment (PWHT). Thus, the AZ31B alloy was welded by using a low-power pulsed Nd:YAG laser-arc hybrid welding equipped on the six-axis welding robot in the present study. Microstructure, mechanical properties and strain-hardening behaviors of the AZ31B joints under various post-weld heat treatment (PWHT) temperatures were characterized. As the heat treatment temperature increases, the grain size of the welded joint gradually increases, and the amount of β-Mg17AI12 phase noticeably decreases. The mechanical properties of the welded joint specimens showed a significant enhancement when subjected to heat treatment at 300 °C and 350 °C for 20 min. Especially, after 350 °C heat treatment for 20 min, the ultimate tensile strength (UTS) and elongation (EL) of specimen were 339.6 MPa and 20.1%, respectively, which were up to 99.5% and 98.5% of the AZ31B base material (BM). The strain-hardening capacity of specimens is significantly influenced by the grain size. Due to having the largest grain size, the 400–20 min specimen exhibited the highest hardening capacity and strain hardening exponent. In Kocks-Mecking type curves, both stage III and stage IV were observed in BM and joint specimens. At higher net flow stresses, the strain hardening rate in the 400–20 min joint specimen was higher due to the larger grains, which allowed for more dislocation accommodation and improved the capacity for dislocation storage.

As a typical spinel structure material, ZnMn2O4 has been widely researched in the field of electrode materials. However, ZnMn2O4 nanoparticles as electrode materials for supercapacitors have the disadvantages of low conductivity, inferior structural integrity, and easy aggregation, resulting in unsatisfying electrochemical performance. In this work, we use a hydrothermal method and high-temperature calcination to deposit ZnMn2O4 nanoparticles on carbon cloth and explore the influence of hydrothermal reaction time on the deposition morphology and distribution of ZnMn2O4 nanoparticles on carbon cloth. The deposition process of ZnMn2O4 nanoparticles on carbon cloth was analyzed, and a ZMO-9 electrode was deduced to be the most suitable electrode for supercapacitors. A series of electrochemical performance tests show that the ZMO-9 electrode has excellent specific capacitance (specific capacity) (499 F·g−1 (299.4 C·g−1) at a current density of 1 A·g−1) and rate performance (75% capacitance retention at a current density of 12 A·g−1). The assembled asymmetric supercapacitor has an energy density of 46.6 Wh·kg−1 when the power density is 800.1 W·kg−1. This work provides a reference for the structural design of ZnMn2O4 supercapacitor electrode materials and the improvement of electrochemical properties.

Nanocrystalline (NC) magnesium alloys and composites present potential for improving energy efficiency in transportation applications due to outstanding strength. Unfortunately, softening owing to grain growth at elevated temperature would induce fatal invalidity. The NC SiCp/AZ91 composite was isothermally annealed. A study on the thermal stability, including phase transformation, grain growth, softening, and strengthening mechanisms was carried out. After annealing treatment at 673 K for 240 min, the average grain size of AZ91-15vol.%SiCp composite increased from 29.0 nm to 53.1 nm. Coherent interface between nano-scale Mg17Al12 precipitates and Mg matrix was certified by HRTEM. Pinning effect due to the dispersing submicron SiC particles with size of 164 nm and nano-scale Mg17Al12 precipitates and dragging effect due to dissolving Al element were the reasons for excellent thermal stability. After annealing treatment, the hardness values of AZ91-xvol.%SiCp (x = 5, 10 and 15) composites were 1.61 GPa, 1.48 GPa and 1.78 GPa. Taking annealed AZ91-15vol.%SiCp composite as an example, there was no evident softening phenomenon and the decreasing ratio was ∼2% in comparison with milled composite with hardness of 1.82 GPa. Non-thermal sensitive SiC particles and high thermal stability Mg matrix played a key role in non-softening of composites.

In this study, Mg–6.0Zn–3.0Sn–0.5Mn (ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid, and a phosphate conversion coating (PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid, exhibited excellent corrosion resistance and behavior.

Abstract The Ce0.8Gd0.2O2−δ (CGO) interlayer is commonly applied in solid oxide fuel cells (SOFCs) to prevent chemical reactions between the (La1−x Sr x )(Co1−y Fe y )O3−δ (LSCF) oxygen electrode and the Y2O3-stabilized ZrO2 (YSZ) electrolyte. However, formation of the YSZ–CGO solid solution with low ionic conductivity and the SrZrO3 (SZO) insulating phase still happens during cell production and long-term operation, causing poor performance and degradation. Unlike many experimental investigations exploring these phenomena, consistent and quantitative computational modeling of the microstructure evolution at the oxygen electrode–electrolyte interface is scarce. We combine thermodynamic, 1D kinetic, and 3D phase-field modeling to computationally reproduce the element redistribution, microstructure evolution, and corresponding ohmic loss of this interface. The influences of different ceramic processing techniques for the CGO interlayer, i.e., screen printing and physical laser deposition (PLD), and of different processing and long-term operating parameters are explored, representing a successful case of quantitative computational engineering of the oxygen electrode–electrolyte interface in SOFCs.

In the present study, the microstructure and mechanical properties of a new Mg-4Al-3.5Ca-2Gd (AXE432) alloy are investigated. The microstructure of the as-cast AXE432 alloy consists of α-Mg, C14 (Mg2Ca), and C36((Mg, Al)2Ca) phases. After the heat treatment at 480 °C for 8 h, the C14 with fine lamellar structure changes from narrow stripes to micro-scale particles, and part of the C36 and the C14 dissolve into the α-Mg matrix, with many short needle-shaped C15 (Al2Ca) phase precipitating in the primary a-Mg grains. The AXE432 alloy extruded at a temperature as high as 420 °C exhibits a refined dynamically recrystallized (DRXed) microstructure with grain sizes less than 1.5 ± 0.5 μm and a strong {0001}1¯0> basal texture with a maximum intensity of 5.62. A complex combination of the effects from grain size, texture, second-phase particles, and strain hardening results in balanced mechanical properties, with the tensile yield strength (TYS), ultimate tensile strength (UTS), elongation (El), compressive yield strength (CYS), and ultimate compressive strength (UCS) of 331.4 ± 2.1 MPa, 336.9 ± 3.8 MPa, 16.1 ± 2.3%, 270.4 ± 1.6 MPa and 574.5 ± 12.4 MPa, respectively.

The effects of mold temperatures on the microstructures and mechanical properties of thixoforged Grp (graphite particles)/AZ91D composites have been investigated, followed by partial remelting and thixoforging technology. The results indicate that the best semi-solid microstructure could be obtained after being partially remelted at 600 °C and held for 60 min. Correspondingly, under a mold temperature of 300 °C, the best tensile properties were obtained by thixoforging. The UTS (ultimate tensile strength) and elongation of the thixoforged Grp/AZ91D were up to 304.1 MPa and 13.9%, respectively, which increased 11.3% and 43.1% in comparison with the thixoforged AZ91D, respectively. The variation of the tensile properties responded to the influences of mold temperatures on the amount of eutectic phase, the distribution of Grp, and the grain size of α-Mg. Meanwhile, HRTEM (High Resolution Transmission Electron Microscope) showed good bonding between Grp and AZ91D, and many edge dislocations were found in the inverse FFT (Fast Fourier Transform) image. And the result showed that the increase in tensile properties is attributed to the synergistic effect of load transfer, dislocation strengthening, and Orowan looping mechanisms from the Grp strengthening the matrix.

The effects of Grp (graphite particles) addition and holding time on the microstructure and mechanical properties of the Grp/AZ91D composite were investigated in this work. The results indicated that the distribution of Grp in the matrix was determined by the self-stabilizing mechanism and relationships between the solidifying interface and the particles. Due to the self-stabilizing mechanism, a small amount of Grp would uniformly distribute in the melt alloy, and as the amount of Grp increased, agglomeration would occur. Accordingly, the former would be engulfed by the solidifying interface and the latter would be pushed. With an increased holding time, Grp tended to agglomerate, due to the interfacial reaction that occurred, and as a result, the solidifying interface will push it. The Grp/AZ91D composite with the addition of 1.5 wt.% Grp and a holding time of 15 min obtained grains 30.2 μm in size with a hardness of 89.07 HV, which was a decrease of 83.04% and increase of 35.06% compared to AZ91D, respectively.

KTaO3 and KNbO3, two typical perovskite ferroelectric crystal materials with identical cubic structure at high temperature, undergoes totally different phase transition path. The underlying mechanism is explored by comparing their phonon anharmonic behavior based on first-principle calculation. The results of Grüneisen parameters indicate larger phonon anharmonicity of KNbO3 than that of KTaO3, which leads to structural unstable of KNbO3. Different with previous studies of soft mode theory, apparent phonon anharmonicity of both crystals are stemmed not from the center, but the corner and boundary of the first Brillouin zone. In order to essentially understand the difference in the anharmonic behavior of phonons, the chemical bond strength of these two perovskite materials was analyzed by ELF. The results show that due to the stronger covalent properties of Ta-O bond, it will cause weak phonon anharmonicity, and ultimately lead to high phonon relaxation time and low Grüneisen parameters of KTaO3. The weakly ionic Nb-O bond give rise to the obvious phonon anharmonic behavior and lattice instability of KNbO3, resulting in a series of temperature-dependent phase transitions.

This study is based on the tunnel-face slope engineering of Dongfeng tunnel in Shanxi section of China’s Shuozhou-Huanghua Railway. The sandstone specimens in the perennial freeze-thaw zone of the slope were collected to carry out freeze-thaw cycle static physical mechanics test and split Hopkinson pressure bar (SHPB) dynamic mechanical test. Thus, the damage process of sandstone under freeze-thaw cycle and impact load is studied. Also, the dynamic compressive strength and dynamic elastic modulus of sandstone are analysed under different loading strain rates and freeze-thaw cycle based on LS-DYNA, a dynamic finite element program. The results showed that the dynamic compressive strength of sandstone subjected to multiple freeze-thaw cycles under 0.04 MPa air pressure has a greater damage ratio than that under 0.055 MPa and 0.07 MPa air pressure, which was more likely to cause damage to slope sandstone than in actual engineering; the dynamic compressive strength and elastic modulus of sandstone decrease greatly within a certain range of freeze-thaw cycles and loading strain rate, leading to significant deterioration. When the freeze-thaw cycle exceeded 200 times and the strain rate was greater than 200 s−1, the physical and mechanical properties of sandstone gradually tended to be stable.

In Southwest China, most regions are mountainous, where traditional drill-and-blast method is adopted to excavate relatively harder rocks. However, blasting would cause vibration to adjacent structures and might result in damage or even failure. This paper considers a case where subway tunnel is overlying an existing railway tunnel, while the excavation requires blasting method. Vibration and stress distribution are calculated via Dynamic Finite Element Method (DFEM) for both full-face excavation and CD method. Result shows that vibration induced by CD method is only 28% of that caused by full-face blasting with same distance. Peak vibration is located on the lining facing the blasting source, while peak tensile stress is on the other side of the contour due to the reflection of stress wave on strata boundary. And peak value of tensile stress induced by full-face blasting is capable of causing lining failure; thus full-face blasting is not suggested within 40 m beyond the underlying tunnel axis. However, CD method has shown much advantage, since blasting within 25 m is also considered safe to the underlying tunnel. But when the blasting source is as near as 12 m within the underlying tunnel, the CD method is no longer safe.

The mechanical behaviors of the thixoforged in situ Mg2Sip/AM60B composite at elevated temperatures were evaluated. The results indicated that the thixoforged composite exhibits higher UTS (ultimate tensile strength) than that of the thixoforged AM60B at the cost of elongation. As the testing temperature rises from 25 to 300 °C, the UTS of both these two materials decreases while their elongations increases. The enhanced dislocation motion ability, the softened eutectic β phase at 120 °C, the activated non-basal slipping and the dynamic recovery and recrystallization mechanisms at 150 °C are responsible for the change in tensile properties with testing temperatures. The fracture mode transforms from the ductile into the brittle as the initial strain rate increases from 0.01 to 0.2 s−1 at 200 °C.