Influence of solution treatment on microstructure and mechanical properties of a near β titanium alloy Ti-7333

The effect of solution treatment on the microstructure and mechanical properties of Ti-7333, a newly developed near β titanium alloy, was investigated. Compared to Ti-5553 and Ti-1023, Ti-7333 possesses the slowest α to β dissolution rate, allowing a wider temperature window for processing. The rate of β grain growth decreases with the increase of soaking time and increases with the increase of solution temperature. The β grain growth exponents (n) are 0.30, 0.31, 0.32 and 0.33 for solution treatment temperature of 860 °C, 910 °C, 960 °C and 1010 °C, respectively. The activation energy (Q_g) for β grain growth is 395.6 kJ/mol. Water cooling or air cooling after solution treatment have no significant influence on microstructure, which offers large heat treatment cooling window. However, under furnace cooling, the fraction of α phase increases sharply. α phase maintains strictly the Burgers orientation relation with β phase ({0 0 0 1}_α//{1 1 0}_β and 〈1 1 −2 0〉_α//〈1 1 1〉_β), except the α_p particles formed during forging. The tensile strength decreases with the increase of the solution temperature when only solution treatment is applied, whereas the ductility increases gradually. When aging is applied subsequently, the tensile strength increases with the increase of the solution temperature and the ductility decreases gradually.     

Stabilization of Colloidal Crystals Engineered with DNA

A postsynthetic method for stabilizing colloidal crystals programmed from DNA is developed. The method relies on Ag⁺ ions to stabilize the particle‐connecting DNA duplexes within the crystal lattice, essentially transforming them from loosely bound structures to ones with very strong interparticle links. Such crystals do not dissociate as a function of temperature like normal DNA or DNA‐interconnected superlattices, and they can be moved from water to organic media or the solid state, and stay intact. The Ag⁺‐stabilization of the DNA bonds is accompanied by a nondestructive ≈25% contraction of the lattice, and both the stabilization and contraction are reversible with the chemical extraction of the Ag⁺ ions, by AgCl precipitation with NaCl. This synthetic tool is important, since it allows scientists and engineers to study such crystals in environments that are incompatible with structures made by conventional DNA programmable methods and without the influence of a matrix such as silica.     

Relationship Between the Swelling Process and the Release of a Water-Soluble Drug from a Compressed Swellable-Soluble Matrix of Poly(Vinyl Alcohol)

An attempt was made in this study to relate the release of a highly water-soluble model drug from tablet matrices of poly(vinyl alcohol) (PVAL) with the factors that may affect the release behavior. Swelling was evaluated using a simple projection method. The swollen layer was photographed to monitor its thickness. The polymer and drug dissolution were determined simultaneously by spectrophotometric methods. The resulting change of tablet area showed that the process of swelling occurred in three different stages that were intimately related to polymer dissolution: (a) a rapid initial swelling, resulting in an increased area; (b) a period with an approximately constant area; and (c) a decrease of the tablet area. In spite of the significant dissolution of PVAL during the release process, the thickness of the gel layer gradually increased. Thus, the delivery was governed by the drug concentration gradient along the diffusional path length. The drug release appeared to be controlled by a diffusion process according to Higuchi-type kinetics. The data analysis of drug and polymer profiles confirmed the diffusional mechanism.     

热处理对Ti-6Mo-5V-3Al-2Fe-2Zr合金拉伸性能的影响

研究了固溶+单级时效处理、固溶+双级时效处理、固溶+随炉冷却处理对新型亚稳β钛合金Ti-6Mo-5V-3Al-2Fe-2Zr的显微组织和拉伸性能的影响。结果表明：与固溶+单级时效处理相比,固溶+双级时效处理析出的晶内次生α相间距减小和体积分数增大而使合金的强度提高。两种热处理都使合金中生成连续的晶界α相,导致合金的塑性降低;与上述两种热处理相比,固溶+随炉冷却处理使合金中析出的晶内次生α相的间距明显减小且沿晶界生成向晶内生长的α_wgb相,使合金的强度和塑性显著提高,其抗拉强度达到1421 MPa,断后伸长率为7.7%;与次生α相的体积分数相比,其间距是影响合金强度的主要因素。随着次生α相间距的减小,合金的强度提高。     

Morphology characteristics of α precipitates related to the crystal defects and the strain accommodation of variant selection in a metastable β titanium alloy

Profound and comprehensive investigations on the morphology characteristics of α precipitates are essential for the microstructural control of metastable β titanium alloys.At the very beginning of aging treatment,intragranular α precipitates with a dot-like morphology begin to generate nearby the dislo-cations,then those dot-like α precipitates with the same crystallographic orientation tend to connect with each other to develop a lath-like morphology.With the progress of aging treatment,the orientated lath-like α precipitates gradually combine with each other to form the V-shaped clusters or the triangular ones.The dislocations of{1(-1)0}β < 11 (-1)>β edge type are evidenced within the β grains,and it is found that variant selection ofα precipitates induced by the transformation strain and the interplay between α vari-ants and the dislocations are confirmed as the key factors for the formation of the V-shaped or triangular clusters.The results of this work could provide underlying knowledge on the morphology characteristics of intraguranular α precipitates related to the crystal defects and the strain accommodation of α variants in metastable β titanium alloys.     

Meropenem–Clavulanate: A New Strategy for the Treatment of Tuberculosis?

The Great White Plague : Mycobacterium tuberculosis, the bacteria causing tuberculosis, is a continuing threat to global health through the emergence of resistant strains and the lack of novel therapeutic agents. Recently reported results on this important work are highlighted.

     

Syngas to iso-paraffins over Co/SiO2 combined with metal/zeolite catalysts

Selective production of gasoline ranged iso-paraffins from synthesis gas was performed in a consecutive dual reactor system, in which Fischer–Tropsch reaction was carried out over Co/SiO₂ catalyst in the upper reactor and hydroconversion of the Fischer–Tropsch hydrocarbons occurred over precious metal/zeolite catalyst in the lower reactor. Results indicate that the product distribution of traditional Fischer–Tropsch synthesis was significantly modified and high selectivity to iso-paraffins was achieved with the presence of metal/zeolite catalyst in the lower reactor. A significant effect of metals (Pt and Pd), zeolites (zeolites of β and USY), and the preparation methods (impregnation and ion exchange) of the metal/zeolite catalyst on the iso-paraffins selectivity and product distribution was clearly observed. This was explained based on the property of the metal for hydrogen spillover and the acidic and structural properties of the zeolite in the bifunctional metal/zeolite catalyst.     

Characterization of hot deformation and microstructure evolution of a new metastable β titanium alloy

The hot deformation characteristics of as-forged Ti?3.5Al?5Mo?6V?3Cr?2Sn?0.5Fe?0.1B?0.1C alloy within a temperature range from 750 to 910 °C and a strain rate range from 0.001 to 1 s^?1 were investigated by hot compression tests. The stress?strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate. The microstructure is sensitive to deformation parameters. The dynamic recrystallization (DRX) grains appear while the temperature reaches 790 °C at a constant strain rate of 0.001 s^?1 and strain rate is not higher than 0.1 s^?1 at a constant temperature of 910 °C. The work-hardening rate θ is calculated and it is found that DRX prefers to happen at high temperature and low strain rate. The constitutive equation and processing map were obtained. The average activation energy of the alloy is 242.78 kJ/mol and there are few unstable regions on the processing map, which indicates excellent hot workability. At the strain rate of 0.1 s^?1, the stress?strain curves show an abnormal shape where there are two stress peaks simultaneously. This can be attributed to the alternation of hardening effect, which results from the continuous dynamic recrystallization (CDRX) and the rotation of DRX grains, and dynamic softening mechanism.     

一种新型亚稳β钛合金热变形的本构模型(英文)

基于新型亚稳β钛合金Ti2448在温度1023～1123K、应变速率63～0.001s-1下的等温热压缩流动应力曲线特征,构建能够完整描述该合金流动应力与应变、应变速率、变形温度之间关系的本构模型。在此过程中,通过基于统一黏塑形理论改进双曲正弦函数,构建合金在高应变速率(≥1s-1)下发生动态回复(DRV)的模型;通过对标准的Avrami方程进行简化,表征了Ti2448在低应变率(1s-1)下发生的动态再结晶(DRX)软化机制。最终通过应用全局优化求解非线性方程的新方法确定模型中的相关参数。根据所建模型得到的预测曲线和实验曲线吻合得较好,能够有效预测Ti2448在热变形过程中的流动应力,为构建亚稳β钛合金热变形本构模型提供一种有效的方法。     

高熔体流动速率β晶型聚丙烯的研制

研究了β晶型成核剂(酰胺化合物)、过氧化物对高熔体流动速率聚丙烯Z3 0S的力学性能、熔体流动性能的影响。通过广角X射线衍射、DSC分析和偏光显微镜观察表明,β晶型成核剂促使生成 β晶型聚丙烯,使聚丙烯的球晶细密化,因而聚丙烯Z3 0S的冲击性能提高