The discovery of iron-based superconductors has offered a new material family for exploring the mechanism of high-temperature superconductivity. 122-type iron-based superconductors has been widely studied by various researchers due to the easy fabrication for the parent compounds of 122-type iron arsenic matrix of high-quality single crystals of large-size. However, which do not intrinsically exhibit superconductivity. Generally, superconductivity is induced through chemical doping to introduce electrons, holes or chemical pressure in these compounds. This paper summarizes several fabrication methods on the single crystals of 122-type iron-based superconductors, including the flux method, Bridgman method, and optical floating zone method. The related research progress of these crystal growth methods are also reviewed. Besides, the recent rsearch progress related with chemical dopingof 122 iron arsenic superconductors, such aselectron doping, hole doping and isovalent doping etc. is also summerized.
In2Se3 has recently received much attention because of its excellent ferroelectric, thermoelectric, and photoelectric properties. However, the stacking defects, known as an important factor affecting the properties of van der Waals layered materials, have not yet been explored for In2Se3. Herein, the atomic configurations of stacking defects in van der Waals layered β-In2Se3 were studied by means of aberration-corrected scanning transmission electron microscopy combined with first-principles calculations. There are a significant amount of replacement-type stacking faults (RSFs) and slip-type stacking faults (SSFs) in 2H β-In2Se3. Moreover, the 1T phase slip-type stacking fault (tSSF), which is thermodynamically prone to spontaneous formation, was observed in 2H β-In2Se3. However, only the SSF was observed as a high energy configuration in 3R β-In2Se3. The phase separation occurred between 2H and 3R β-In2Se3 with a coherent stacking interface. In addition, nine potential stacking fault configurations of β-In2Se3 were constructed, the corresponding stacking fault energies were calculated, and the causes of stacking faults were analyzed from an energetic perspective. Finally, the need for a classification term describing the stacking faults in van der Waals-like layered materials is pointed out.
The hot deformation behavior of 6013 Al-alloy at 530~575oC and strain rate of 0.001~0.1 s-1 was studied by hot compression simulation test. Based on the electron backscatter diffraction technique, the microstructure evolution and dynamic softening mechanism were discussed, while the so called Zener-Hollomon (Z) parameter was adopted to represent the combined effect of deformation temperature and strain rate. The results show that the flow stress of the alloy increases with the increase of ln Z, and the deformation activation energy of the alloy under steady state condition is 217.3 kJ/mol. With the increase of lnZ, the recrystallization area fraction and sub-grain size tend to decrease linearly. For 23.91 ≤ lnZ < 29.55, dynamic recrystallization is the main softening mechanism, in which geometric dynamic recrystallization is dominant. For 29.55 < lnZ ≤ 30.24, dynamic recovery is the main softening mechanism.
Two type powders of CoNiCrAlY alloy were prepared by gas atomization (GA) and water atomization (WA) respectively, then which were used as feedstock powders to further prepared the corresponding coatings on a directionally solidified high temperature alloy DZ411by using high velocity oxygen fuel (HVOF) technique and subsequently they were subjected to proper subsequent vacuum heat treatment. The flowability and apparent density of the prepared powders were measured according to GB/T 1484 and GB/T 1479. Meanwhile, the phase composition, microstructure, microhardness, and adhesive strength to the substrate of the prepared coatings were characterized via optical microscopy and scanning electron microscopy, automatic hardness tester, and universal testing machine. The high temperature oxidation performance of the coatings/ DZ411 was assessed in air at 1050oC for 200 h. The results show that compared with WA, the CoNiCrAlY powder prepared by GA is spherical or nearly spherical, with good flowability and high apparent density. The prepared GA coating has a dense and uniform structure with high β phase content, low porosity, high adhesive strength and high microhardness. After vacuum heat treatment, mutual fusion of particles was clearly observed within the two coatings, while the amount of β phase increases and its distribution becomes much more uniform, correspondingly, their porosity and microhardness decrease. The adhesive strength of WA coating after vacuum heat treatment has been improved, but there are still larger pores within the coating. The vacuum heat treated GA coating presents much better oxidation resistance.
By aging treatment of a medium manganese lightweight steel at 550oC, the evolution of its microstructure and mechanical properties was analyzed. The results indicate that aging treatment has a significant impact on precipitates. When the aging time is less than 30 minutes, a large number of intragranular κ'-carbides formed by spinodal decomposition, which distributed dispersedly in the austenite matrix. As the aging time increases, besides the intragranular κ'-carbides, intergranular κ-carbides are also formed at grain boundaries through eutectoid reactions as a layered structure of α ferrite and κ-carbide. Intragranular κ'-carbides greatly increase the strength, but intergranular κ-carbides significantly reduce the ductility of the steel. Compared with long-time aging, the strength of the steel can be significantly increased by short-time aging, while the steel still maintains a high elongation with better overall mechanical properties. Among them, the good performance is achieved for the steel after aging for 30 minutes, namely a tensile strength of 1031 MPa, yield strength of 784 MPa, an elongation of 41.08%, and a product of strength and elongation of 42.35 GPa·%.
The high strength, high temperature resistance and high thermal shock resistance of ceramic nanofibers are essential to high temperature thermal insulation materials, which have good application prospects in aerospace and other fields. The low thermal conductivity and good infrared refractive index of ZrO2 nanofibers have attracted much attention in the field of thermal insulation. However, the poor thermal stability (≤ 1200oC) of ZrO2 nanofiber limits their utilization in the field of high-temperature thermal insulation. In this study, a novel membrane of SiO2/ZrO2-0.5 nanofibers (d = 495.8 ± 45.5 nm) with high temperature resistance up to 1300oC was prepared by combining electrospinning technology and preceramic polymer pyrolysis method, the SiO2/ZrO2-0.5 nanofiber composed of amorphous SiO2 phase and t-ZrO2 nanocrystalline. The fabricated SiO2/ZrO2-0.5 nanofiber membrane shows high tensile strength (4.88 ± 0.27 MPa), good flexibility and excellent thermal insulation performance at high temperatures. Finally, it is worth noting in particular that the thermal conductivity of SiO2/ZrO2-0.5 nanofiber membrane is only 0.167 W·m-1·K-1 at 1000oC, which is significantly lower than those of the known traditional ceramic fiber membranes.
Metal-organic framework (MOF) glass with characteristics of porous and easy forming, shows broad application prospects in the fields of adsorption and separation. However, the porous structure will collapse and deform during the formation of MOF glass, which limits the separation performance of MOF glass, besides very few MOFs have been found so far. In this work, a novel MOF glass agSALEM-2 was prepared via successively melting and quenching processes, with MOF crystal SALEM-2 as precursor, which not only has a fusible chemical composition but also an abundant pore structure. The prepared melting-quenching process of SALEM-2 was investigated by means of XRD, SEM and TIG etc. The results show that before melting, the SALEM-2 undergoes thermally amorphization, recrystallization and decomposition processes sequentially; during melting, a part of the organic ligands 2-methylimidazole (MIm) in SALEM-2 decomposes to generate defects, leading to a lower melting point; during quenching, the MIm can prevent the re-formation of the framework structure and thus partially preserves its porous structure in the liquid state, the higher the quenching rate, the higher the degree of retention of the porous structure in the liquid state. Thus, the porous glass agSALEM-2 with a BET specific surface area of up to 150 m2/g was successfully prepared. This study enriches the variety of MOF glass materials and provides an effective strategy to enhance the porosity of MOF glasses.
Coal fly ash (CFA) was modified with HCl and NaOH solutions as to produce a novel modified porous adsorbent (MCFA). The CFA and MCFA were characterized by SEM、BET、FT-IR、XRD、XPS. Meanwhile, simulated wastewaters containing dyes, such as basic violet, basic green, Congo red, and methyl violet, respectively were prepared, then the effect of the MCFA dosage on the adsorption capacity for dyes, and the effect of pH value of wastewaters on adsorption capacity for dyes were examined. The characterization results showed that the surface of MCFA is rather rough and porous, with a specific surface area of 32.0 m2/g, superior to 5.2 m2/g of the original CFA, accordingly its adsorption performance may be enhanced due to the increasing active and adsorptive sites on the surface. The MCFA has excellent adsorption effect on the desired four dyes. The maximum removal efficiency of basic violet and basic green all reached 99%, respectively by using adsorbent dosage of 2 mL for a given dye solution of 100 mg/L. By fitting data with isothermal adsorption and kinetic models, it follows that Freundlich isotherm model was fitted for the adsorption process, and both physical and chemical adsorption are involved in the adsorption process. The adsorption behavior of all four dyes could be described better by pseudo-second-order kinetics rather than pseudo-first-order kinetics, and the adsorption effect was significant, which can be used as an excellent adsorbent in the treatment industry of dye wastewaters.
A novel secondary hardened steel 25CrMo3NiTiVNbZr was developed via optimization the chemical composition of the 25Cr3Mo3NiNbZr steel bymeans of the so called JMatpro and Thermo-Calc software. Then the microstructure, phase composition, morphology of precipitates and mechanical performance at 700℃ of the 25CrMo3NiTiVNbZr steel were characterized by means of transmission electron microscopy (TEM), electron backscattering diffraction (EBSD), while its the high-temperature streng-thening mechanism was also elucidated. The results show that the tensile strength and yield strength of 25CrMo3NiTiVNbZr steel at 700oC are 543 MPa and 409 MPa, respectively, which are 139 MPa and 123 MPa higher than that of 25Cr3Mo3NiNbZr steel. The high-temperature strengthening of the 25CrMo3NiTiVNbZr steel may mainly ascribed to themechanism, precipitation strengthening. In the process of being stretched at 700oC, the precipitation strengthening increment derived from the precipitation of the strengthening phase for the 25CrMo3NiTiVNbZr steel reached 367 MPa, which was 147 MPa higher than that of the 25Cr3Mo3NiNbZr steel. This is mainly due to the higher thermal stability and smaller size (average size at 7.93 nm) of the precipitated strengthening phases in the 25CrMo3NiTiVNbZr steel. After high-temperature stretching, the average size of precipitates remained at 8.14 nm.
