As an emerging two-dimensional transition metal carbide or carbonitride, MXene exhibits excellent metallic conductivity, abundant surface functional groups and ultrathin two-dimensional structure, which endows it great potential in electrochemical energy storage. Lithium-sulfur batteries have a high theoretical specific capacity and become a very competitive choice in the new generation of energy storage devices. Two-dimensional MXenes and the assembled three-dimensional materials, as advanced sulfur carriers, can effectively improve the inherent poor conductivity and serious dissolution of discharge products of lithium-sulfur batteries. This paper reviews the current applications of MXene materials with two-dimensional and three-dimensional structures in lithium-sulfur batteries, analyzes the relationship between different structures and performance, summarizes the current challenges and difficulties, and gives a view on the direction to proceed for future designs.

With the increasing cleanliness of steels in recent years, it has made possible for making micro-alloyed steels with rare earth elements. It is found that the addition of rare earths has a significant effect on the solid-state phase transformation behavior of steels, especially for low-carbon low-alloy steels. The effectiveness in modifying the inclusions and inducing nucleation by RE addition has been studied intensively and approved substantially. Whereas, the micro-alloying effect of RE on the ferrite phase transformation of steel is still unclear. The effect of rare earth elements (RE) on austenite-ferrite transformation temperature during continuous cooling, and the isothermal transformation kinetics of Fe-C alloys and Fe-C-Si-Mn low carbon steels has been investigated in this article. It is found that a tiny amount of RE addition can reduce the starting point temperature of proeutectoid ferrite during continuous cooling. Additionally, the addition of RE also changes the ferrite transformation kinetics in the isothermal process: for Fe-C-(RE) alloys, the addition of RE slows down the transformation rate during the whole transformation process due to the pinning carbon diffusion effect; For Fe-C-Si-Mn alloys, RE elements can play a double role of pinning carbon diffusion and changing grain boundary energy, and then prolong the incubation period and decreases the rate of phase transformation during the initial stage, while increase the phase transformation rate during the middle and late of phase transformation.

The effect of different solution temperatures on the micro-substructure and γ' phase of GH4742 superalloy were studied by EBSD and TEM, and the mechanical properties of GH4742 superalloy were measured. The results show that the proportion of static recrystallization of matrix increased with increasing solution temperature in the range of 1080℃ to 1120℃, which resulted in the decrease of the proportion of low-angle grain boundaries from 13.2% to 3.2%; Meanwhile, the grains were significantly coarsened with a size increase from 11.0 μm to 111.6 μm, the proportion of Σ3 twin boundary increased from 13.2% to 58.6%. The volume fraction of the primary γ' phase in the matrix decreased evidently with the increase of the solution temperature, while the size of the primary γ' phase increased, and the volume fraction and size of the secondary γ' phase increased continuously, and that of the tertiary γ' phase changed little. The variety of strengthening contribution of γ' phase was small by different solution temperatures, and the strengthening increment caused by grain boundary strengthening plays determine role in the strength of the matrix. The room temperature strength of GH4742 alloy decreased dramatically with the increase of solution temperature, while the high temperature strength and rupture fracture time increased markedly. The GH4742 alloy solution treated at 1100℃ exhibits good mechanical properties at either room temperature or high temperature.

The low-cycle fatigue behavior of TC4 ELI (Extra-low-interstitial) alloy plates for pressure shells in deep-sea submersible with different notch stress concentration factors under constant total strain amplitude was investigated. The results indicate that cyclic harding and cyclic softening occur in the smooth specimens under the lower strain amplitude (≤0.7%) and higher strain amplitudes (0.8% and 0.9%), respectively, at the initial stage of the cyclic loading. While the cyclic hardening occurs in all the notched specimens under the strain amplitudes of 0.2% to 0.7% at the initial stage of the cyclic loading. Based on the variation of material hysteretic energy under the cyclic loading, a relative crack initiation life prediction model was established to describe the damage degree of TC4ELI alloy specimens under the low cycle fatigue loading. The relationship between notch stress concentration factors and low cycle fatigue performance parameters was also described. This model can effectively predict the relative fatigue crack initiation life of TC4ELI alloy with low notch stress concentration factor under high strain amplitude conditions.

Cyclic oxidation resistance is an essential factor affecting the reliable use of Ti65 Ti-alloy plates in aerospace vehicles. In this paper, the cyclic oxidation resistance of Ti65 plates was investigated by cyclic oxidation testing at 650℃~800℃. The results showed that the NiCrAlSiY coated Ti65 plate was composed of three regions after 500 cycles of oxidation test: coating, diffusion layer, and substrate region. The interface of coating/plate was relatively compact, and the coated plate exhibited a fully antioxidant level. The major oxide on the surface of coated plate was found to be Al₂O₃, while TiO₂ was detected when oxidation temperature increased to 800℃. During cyclic oxidation, the elements diffusion between coating and substrate were mainly Ni and Ti, while the diffusion of a small amount of Cr occurred when temperature increased to 800℃. The inter-diffusion of Ni and Ti were thought to lead to the generation of Ti₂Ni and TiNi at coating/plate interface. After cyclic oxidation, the tensile strength retention of both coated and as-received plates were more than 90%, while the elongation of coated plates was only about 30% of the original plates (before cyclic oxidation). The plates without coating were failed by brittle fracture after cyclic oxidation, obviously, the significant reduction of tensile elongation might be due to the brittleness caused by infiltration of oxygen element at high temperature on the plate surface.

The microstructure and crystallographic structure characteristics of as cold-rolled strip and foil with different thicknesses of GH3536 alloy after annealing was investigated by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD) to get an insight into the recrystallization and grain growth behavior. The results show that the cold rolled strip and foil of GH3536 alloy show a microstructure composed of elongated grains along the rolling directions, and its main phase was γ. The grain growth equations of the strip and foil with thicknesses of 200,100 and 50 μm annealed at 1050~1150℃ for 10~60 min were established respectively, and the relevant activation energies were acquired as follows: Q_{200 μm}=800.34 kJ/mol, Q_{100 μm}=609.50 kJ/mol and Q_{50 μm}=314.79 kJ/mol. The activation energy of the thinner strip and foil was smaller, and the grain growth was more prone to occur. The main factors affecting the grain growth were related to deformation degree and precipitated particles.

Graphene/SiO₂ nanocomposites were prepared by sol-gel method using graphene and Tetraethyl orthosilicate as raw materials. The tribological properties of graphene/SiO₂ nanocomposites as water-based lubrication additives were evaluated by ball-disk friction and wear testing machine under different loads and in the presence of ultra-pure waters with different additive concentrations. The surface morphology and elemental characteristics of the friction pair were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that under the loading condition of 15N, in ultra-pure water with 0.2% (mass fraction) Graphene/SiO₂ nanocomposites as additives the ball-disk pair exhibits the best tribological properties, with the coefficient of friction and the wear rate of the steel ball 17.9% and 61.7% lower, respectively than those in the blank ultra-pure water. Based on the wear surface analysis, the lubrication mechanism is as follows: during the friction process, the physical adsorption film formed by graphene/SiO₂ nanocomposites on the wear surface, the layered shear action of graphene, the repair action of SiO₂ on the wear surface, and the action of ball bearings. All together effectively improve the tribological properties of ultra-pure water.

To search superior photoanode materials for further enhancing the cell performance of quantum dot-sensitized solar cells (QDSSCs), the zero-dimensional SnO₂ may be a good option for its excellent cycling stability, high mobility and bandgap tunability. For this purpose, hollow nanospheres of SnO₂, as the candidate material for scattering layer of the photoanode were synthesized by a simple one-step hydrothermal method, and then screen-printed on the TiO₂ substrate to produce a photoanode for quantum dot sensitized solar cells (QDSSCs), which showed excellent electrochemical performance. It is demonstrated that the hollow sphere structure of SnO₂ facilitates the storage of electrolytes and improves its chemical stability while ensuring an efficient electron transfer rate, allowing the cyclic reaction to proceed more efficiently. ZnCuInSe quantum dots were used as sensitizers for the preparation of QDSSCs. Thus it is meaningfull to investigate the effect of photoanodes with different thickness of TiO₂ films printed with quantum dots on the photovoltaic performance of solar cells. Several sets of test results show that when the thickness of the SnO₂ scattering layer is 9 μm, the photoelectric conversion efficiency reaches a maximum value of 7.31%. This opens up the possibility of using SnO₂ in QDSSCs.