Effects of nano-sized TiB_(2) particles and Al_(3)Zr dispersoids on microstructure and mechanical properties of Al-Zn-Mg-Cu based materials

The effects of TiB_(2) and Zr on the microstructure,aging response and mechanical properties of hot-extruded Al-Zn-Mg-Cu based materials were investigated and compared by multi-scale microstructure characterization techniques.The results showed that proper addition of TiB_(2) particles could refine grain size during solidification,promote dynamic recrystallization during extrusion,and inhibit grain growth during solution treatment.Meanwhile,Zr addition had minor influence on the grain refinement during solidification,but could effectively suppress recrystallization and grain growth compared with the Zr-free alloy.Furthermore,the TiB_(2) addition could simultaneously enhance the aging kinetics and peak-aged hardness of the materials.Comparatively,Zr addition could also improve the peak-aged hardness with minor effect on the aging kinetics of the materials.Finally,the quench sensitivity,elastic modulus and tensile properties of the materials were compared and studied.Specifically,the relationship between the microstructure and mechanical properties,and the strengthening mechanisms were discussed in detail.

Enhanced thermal stability and mechanical properties of high-temperature resistant Al-Cu alloy with Zr and Mn micro-alloying

The high temperature(HT)thermal stability and mechanical properties of Al-5%Cu(AC)and Al-5%Cu-0.2%Mn-0.2 Zr%(ACMZ)alloys from 573 to 673 K were systematically studied.The results displayed that micro-alloying additions of Zr and Mn elements have presented a significant role in stabilizing the main strengthening metastableθ′precipitates at a temperature as high as 573 K.Simultaneously,the HT tensile test demonstrated that ACMZ alloy retained their strength of(88.6±8.8)MPa,which was much higher than that of AC alloy((32.5±0.8)MPa)after the thermal exposure at 573 K for 200 h.Finally,the underlying mechanisms of strength and ductility enhancement mechanism of the ACMZ alloy at HT were discussed in detail.

Capsaicin-induced cell death in a human gastric adenocarcinoma cell line

AIM Capsaicin, a pungent ingredient found in red pepper, has long been used in spices, food additives, and drugs. Cell death induced by the binding of capsaidn was examined in a human gastric adenocarcinoma cell line （AGS cells）. METHODS： By using XTT-based cytotoxicity assay, flow cytometry using the TUNEL method, and quantitation of DNA fragmentation, both cell death and DNA fragmentaUon were detected in AGS cells treated with capsaicin. By using Western blotting methods, capsaicin reduced the expression of Bcl-2, the antiapoptotic protein, in AGS cells in a concentration-dependent manner. RESULTS- After incubation of AGS cells with capsaicin for 24 h, cell viability decreased significantly in a dose-dependent manner. After incubation of AGS cells with capsaicin for 24 h, apoptotic bodies also significantly increased, and were again correlated with the dose of capsaicin. When the concentration of capsaicin was 1 mmol/L, the amount of DNA fragments also increased. Similar results were also in the lower traces. CONCLUSION： These results suggest that capsaicin- induced cell death might be via a Bcl-2 sensitive apoptotic pathway. Therefore, capsaicin might induce protection from gastric cancer.

Effect of Cu element on morphology of TiB2 particles in TiB2/Al-Cu composites

In order to explore the influence of Cu element on the morphology evolution of the in-situ TiB2 particles, the10 wt.% TiB2 reinforced Al-5 wt.%Cu based composite was prepared by mixed salt casting. The morphology characterization and transformation of TiB2 reinforcements caused by Cu element were investigated by multi-scale microstructure characterization and statistics techniques. In the case of controlled casting, 5 wt.% Cu addition was found to transform the TiB2 particle morphology from hexagonal plate with sharp edges and corners to hexagonal or tetragonal prism with chamfered edges and corners with the distinguishing growth steps both on the top surface and the side surface. The TiB2 growth in Al-Cu matrix followed the rules: nano-scaled spherical nuclei-polyhedron grains-chamfered hexagonal particles-hexagonal plates-chamfered particles with obvious growth steps. The adsorption energy of Cu on different crystal surfaces of TiB2 was caculated to reveal the influence mechanism and the results indicated that Cu was preferentially adsorbed on the(10-11)TiB2 crystal planes, devoting to the small aspect ratio of TiB2.

Microstructure and mechanical properties of in-situ TiB_2/A356 composites and a prediction model of yield strength

The in-situ TiB2/A356 composites were successfully synthesized through the mixed salt reaction method. The advantage of this technique was that the particle sizes and morphology can be controlled by the melt reaction. Therefore, the technique can be designed to obtain expected properties, such as high strength at high and room temperatures, high damping capacity, high modulus and good fatigue life. Results showed that in the as-cast state of A356 alloy and TiB2/A356 composites, the eutectic Si phase is normally in the needle shape, and TiB2 particles are mostly in the cubic or near spherical shape, with the size ranging from 30 to 500 nm uniformly distributed in the grains. Also, TiB2 particle clusters are observed in composites. With an increase in TiB2 particles, the average grain size of composites decreases both in as-cast and T6 state. It is found that both the yield stength and ultimate tensile strength increase with an increase in the TiB2 volume fraction. On the contrary, the elongation reduces with the addition of TiB2 particles. Based on the experimental results and Clyne＇s report, a revised model related to particle strengthening mechanism was proposed to fairly predict yield strengths of TiBJA356 composites. The satisfactory agreement between the calculated values and experimental data reported in the literature was obtained.

单体电化学测量银纳米颗粒动态光解过程

银纳米颗粒吸收光后会发生能量转换从而导致其晶体结构变化,分析光解过程中纳米颗粒的物理和化学性质十分重要。本文利用具有高灵敏度、高时间分辨率和高通量性质的单体电化学测量技术,原位实时追踪单个银纳米颗粒的动态光解过程。当银纳米颗粒与限域电极界面碰撞时,其会发生动态氧化,从而产生高通量的法拉第电流信号。激光照射会使银纳米颗粒结构发生变化,导致瞬态电流幅值降低和碰撞频率升高。通过统计高通量计时电流信号,实现了对银纳米颗粒在光照条件下的形貌和结构转变过程的定量评估。研究表明,单体电化学可精准获取光解过程中银纳米颗粒的结构变化信息,揭示颗粒之间物理化学性能的异质性,有助于在单颗粒尺度上对银光解动力学进行深入探究。

Enhanced single-nanoparticle collisions for the hydrogen evolution reaction in a confined microchannel

Single nanoparticle(NP)collisions technique has been widely employed in electrocatalysis.However,the short collision duration of single NPs hinders the further improvement in their electrocatalytic performance.Here,to increase the dynamic collision duration of single NPs in the electron tunneling region,enhanced near-wall hindered diffusion is introduced in the stochastic collision process by coupling a Au ultramicroelectrode(UME)with a confined microchannel.In the case of single palladium nanoparticle(Pd NP)collisions for the hydrogen evolution reaction(HER),the hydrodynamic trapping confined in the microchannel effectively permits the activation of the HER on the single Pd NPs.The microchannel-based Au UME is promising in the application of single-NP collisions to energy conversion.

Fabrication and analysis of TIG welding-brazing butt joints of in-situ TiB2/7050 composite and TA2

Lightweight hybrid structures of Al MMCs and titanium alloy dissimilar materials have great prospect in the defence industry application. So, it is necessary to join Al MMCs with Ti metal to achieve this structural design. In this work, in-situ Ti B_(2)/7050 composite and TA2 were firstly attempted to join by TIG welding-brazing technique. The result was that the intact welding-brazing butt joint was successfully fabricated. The joint presents dual characteristics, being a brazing on TA2 side and a welding on Ti B_(2)/7050 side. At brazing joint side, ER4043 filler metal effectively wets on TA2 under TIG heating condition,and a continuous interfacial reaction layer with 1 e3 mm is formed at welded metal/TA2 interface. The whole interfacial reaction layers are composed of Ti(Al Si)3 intermetallic compounds(IMCs), but their morphologies at the different regions present obvious distinguishes. The microhardness of the reaction layers is as much as 141 e190 HV. At welding joints side, the fusion zone appears the equixaed crystal structure, and the grain sizes are much smaller than those of welded metal, which is attributed to the effect of Ti B2 particulates from the melted Ti B_(2)/7050 on acceleration formation and inhibiting growth for the new crystal nucleus. The tensile test results show that average tensile strength of the optimal welding-brazing joint is able to achieve 138 MPa. The failure of the tensile joint occurs by quasi-cleavage pattern, and the cracks initiate from the IMCs layer at the groove surface of TA2 and propagate into the welded metal.