Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10^-4s^-1to 1 s^-1, the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions（n2and n1） and the transition strain（εL） decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.

Effect of Rare Earths on Solidification Microstructure and High Temperature Mechanical Property of Sn60-Pb40 Solder alloy

Trace rare earth elements were used in order to strengthen the Sn60 Pb40 solder alloy. The experimental results show that the high temperature tensile strength of near eutectic Sn60 Pb40 solder alloy is increased by about 70% after adding trace rare earth elements. Analysis shows that the high affinity between rare earth element and Sn leads to the variation of contact angle at the three phase junction of S/L interface during eutectic growth and further changes the Pb concentration at the S/L interface needed for coupled eutectic growth. Thus the eutectic microstructure can directly grow upon the primary Pb rich phase and the formation of coarse Sn rich halo is suppressed. Therefore homogeneous metallurgical microstructure can be obtained.

Tensile ductility improvement of AlSi9Cu1 alloy by chemical composition optimization

Diesel engines, characterized by higher breakout pressure and compression ratio in comparison with gasoline engines, require particularly elevated tensile properties for their engine parts. In order to maintain both high strength and high ductility in the cylinder head, i.e., to obtain higher percent elongation without further reducing the tensile strength, Al Si9Cu1 alloy was used to prepare the cylinder head in an aluminum diesel engine. At the same time, the effect of different modification elements, Na or Sr, and Fe content on the reduction of secondary dendrite arm spacing(SDAS) was discussed, and the design of T7 heat treatment parameters were analyzed in order to improve the tensile ductility. The result shows:(1) The SDAS is as small as 18±3 μm for the Sr modified alloy.(2) The percent elongation of the alloy with Sr modification increases by 66.7% and 42.9%, respectively, compared with the unmodified alloy and the alloy with Na modification.(3) Lower Fe content alloy(0.10%) gives good results in percent elongation compared to the alloy with higher Fe content(0.27%); in particular, after Sr modification and T7 heat treatment, the elongation of over 5% is obtained.

A cation-dipole-reinforced elastic polymer electrolyte enabling long-cycling quasi-solid-state lithium metal batteries

The application of ionic liquids(IL)in polymer electrolytes represents a safer alternative to the currently used organic solvents in lithium batteries due to their nonflammability and thermal stability.However,as a plasticizer,it is generally agreed that the introduction of ionic liquid usually leads to a trade-off between ion transport and mechanical properties of polymer electrolyte.Here we report the synthesis of an IL-embedded polymer electrolyte with both high ionic conductivity(2.77×10^(-4)S cm^(-1)at room temperature)and excellent mechanical properties(high tensile strength up to 11.4 MPa and excellent stretchability of 387%elongation at break)achieved by strong ion–dipole interactions between polymer electrolyte components,which was unveiled by the DFT calculation.Moreover,this polymer electrolyte also exhibits nonflammability,good thermal stability and the ability to recover reversibly from applied stress,i.e.,excellent elasticity.This highly viscoelastic polymer electrolyte enables tight interfacial contact and good adaptability with electrodes for stable lithium stripping/plating for 2000 h under a current density of 0.1 mA cm^(-2).By coupling with this polymer electrolyte,the LiFePO_(4)/Li cells exhibit outstanding cycling stability at room temperature as well as the reliability under extreme environmental temperature or being abused.

Effect of heating rate on the properties of silicon carbide fiber with chemical-vapor-cured polycarbosilane fiber

Silicon carbide (SiC) fiber has recently received considerable attention as promising next-generation fiber because of its high strength at temperatures greater than 1300 ℃ in air.High-quality SiC fiber is primarily made through a curing and heat treatment process.In this study,the chemical vapor curing method,instead of the thermal oxidation curing method,was used to prepare cured polycarbosilane (PCS) fiber.During the high temperature heat treatment of the cured PCS fiber,varied heating rates of 10,20,30,and 40 ℃/min were applied.Throughout the process,the fiber remained in the amorphous silicon carbide phase,and the measured tensile strength was the greatest when the oxygen content in the heat-treated fiber was low,due to the rapid heating rate.The fiber produced through this method was also found to have excellent internal oxidation properties.This fast,continuous process shows a great promise for the production of SiC fiber and the development of high-quality products.