Search

The strength–ductility mechanism of the low-carbon steels processed by laser cutting is investigated in this paper. A typical gradient-phased structure can be obtained near the laser cutting surface, which consists of a laser-remelted layer (LRL, with the microstructure of lath bainite + granular bainite) and heat-affected zone (HAZ). As the distance from the laser cutting surface increases, the content of lath martensite decreases in the HAZ, which is accompanied by a rise in the content of ferrite. Considering that the microstructures of the LRL and HAZ are completely different from the base metal (BM, ferrite + pearlite), a significant strain gradient can be inevitably generated by the remarkable microhardness differences in the gradient-phased structure. The hetero-deformation-induced strengthening and hardening will be produced, which is related to the pileups of the geometrically necessary dislocations (GNDs) that are generated to accommodate the strain gradient near interfaces. Plural phases of the HAZ can also contribute to the increment of the hetero-deformation-induced strengthening and hardening during deformation. Due to the gradient-phased structure, the low carbon steels under the process of laser cutting have a superior combination of strength and ductility as yield strength of ~487 MPa, tensile strength of ~655 MPa, and total elongation of ~32.7%.

The slow Li+ transport rate in the thick sulfur cathode of the Li--S battery affects its capacity and cycling performance. Herein, Fe-doped highly ordered mesoporous silica material (Fe--HSBA-15) as a sulfur carrier of the Li--S battery shows high ion conductivity (1.10 mS cm-1) and Li+ transference number (0.77). The Fe--HSBA-15/S cell has an initial capacity of up to 1216.7 mA h g-1 at 0.2C and good stability. Impressively, at a high sulfur load of 4.34 mg cm-2, the Fe--HSBA-15/S cell still maintains an area specific capacity of 4.47 mA h cm-2 after 100 cycles. This is because Fe--HSBA-15 improves the Li+ diffusion behavior through the ordered mesoporous structure. Theoretical calculations also confirmed that the doping of iron enhances the adsorption of polysulfides, reduces the band gap and makes the catalytic activity stronger. [ABSTRACT FROM AUTHOR]

Interfacial properties of Li-ion cells containing LiCoO2 and a mixture of natural and artificial graphite in a LiPF6-based nonaqueou electrolyte were studied during storage and operation under various temperatures. The graphite/electrolyte interface showed a higher activation energy of Li-ion transfer than the LiCoO2/electrolyte interface for a cell with 100% state of charge. Li-plating occurred on graphite in charging at low temperature, where the charge transfer resistance of graphite electrode became dominating in the fully charged cell. The instability of solid electrolyte interphase (SEI) film on graphite during storage and cycles led to a decrease in impedance and capacity loss. Mechanisms of reversible capacity loss of an aged cell during storage were discussed. [ABSTRACT FROM AUTHOR]