Room‐Temperature Mechanical Properties of V20Nb20Mo20Ta20W20 High‐Entropy Alloy

Refractory high‐entropy alloys (HEAs) have shown promising high temperature strengths, while their mechanical behaviors at room temperature are rarely reported. In this work, the room‐temperature mechanical properties of V₂₀Nb₂₀Mo₂₀Ta₂₀W₂₀ refractory HEA under various different loading modes including tension, compression, bending, shear loading, and microhardness are investigated. The results show that this alloy exhibits very high compressive strength but quite low strengths under tension, bending, and shear loading, similar to the conventional brittle materials. However, pronounced plasticity and slip bands are observed in compression samples, and no indentation cracking is observed in low‐load microhardness tests, which indicate the potential ability of plastic deformation in this refractory HEA. The present work suggests that the microstructure or composition of this HEA should be carefully tailored before its practical usage to suppress its large tendency for cracking and eventually improve its ductility and strength under tension.

     

Synthesis of MnAPO-20, CoAPO-20, NiAPO-20, and CuAPO-20 using tetrahedral tetrahalometallates

Highly crystalline MnAPO-20 and CoAPO-20 have been prepared at previously unreported substitution levels using tetrahedral tetrahalometallates. X-ray diffraction and infrared spectroscopy indicate that framework substitution of manganese and cobalt has taken place. Samples have also been studied using X-ray fluorescence, scanning electron microscopy, thermogravimetric analysis, and a Gouy balance. MnAPO-20 and CoAPO-20 synthesized with metal(II) acetates using the same molar ratios were not as pure as those synthesized using the tetrahedral complexes even at low substitution levels. Interplanar spacings and unit cell sizes were found to be smaller in these traditionally prepared AlPO₄-20 analogs, indicating less framework incorporation of the transition metal. NiAPO-20 and CuAPO-20 have also been prepared by this method, although framework substitution of Ni(II) and Cu(II) is not confirmed.     

Pseudo-quinary Ti20Zr20Hf20Be20(Cu20 -xNix) high entropy bulk metallic glasses with large glass forming ability

A series of pseudo-quinary Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu_20 -xNi_x) (x = 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 at.%) high entropy bulk metallic glasses (HE-BMGs) with large glass forming ability (GFA) were successfully prepared by copper mold tilt-casing. The critical diameters (D_c) of these HE-BMGs are all above 12 mm. In particular, the developed Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu_7.5Ni_12.5) and Ti₂₀Zr₂₀Hf₂₀Be₂₀Ni₂₀ high entropy alloys (HEAs) can be produced in the amorphous state with diameters up to 30 mm and 15 mm, respectively, which are the largest HE-BMG and quinary HE-BMG hitherto. The two HE-BMGs also exhibit high yield strength, together with the plastic strain values of (3.0 ± 1.1) % and (4.0 ± 0.9) %, respectively. With increasing Ni additions in the pseudo-quinary HEAs, the crystallization growth resistance and thermal stability have been improved, which is apparently due to the sluggish diffusion of the atoms in the HEAs.     

Track nanodosimetry of 20-MeV protons at 20 nm

Track nanodosimetry is the theoretical and experimental research which studies the stochastic aspects of ionisation yield produced by ionising particles in nanometric target volumes, positioned at different distances from the primary particle track. The STARTRACK experimental set-up, mounted on the +50° beam line at the Tandem-Alpi particle accelerator of Legnaro National Laboratories, has been conceived to give an experimental basis to nanodosimetric calculations. STARTRACK is a detection system able to measure the ionisation cluster-size distributions in a 20 nm propane site, by counting the electrons set in motion by different ion tracks, with the resolution of one electron. The 'sensitive volume' SV can be moved at different distances from the primary particle track (different impact parameter). Distributions of 20-MeV protons have been measured and compared with Monte Carlo calculations.     

ZKP—20型二十工位真空开关管排气台

介绍了ＺＫＰ－２０型二十工位真空开关管排气台的结构设计，采用ＰＣ工业程序控制系统，实现了整个排气工艺过程的自动化，降低了操作人员劳动强度，提高了生产效率。     

使用索尼DSC-U20

索尼DSC—U20是索尼公司新推出的一款数码照相机,它是索尼DSC—U10的改进型,照相机的总像素为211万,有效像素从DSC—U10的100万提高到200万,最大分辨率从1280×960提高到1632×1224。     

二十年的设计路

我不是一个喜欢向后看的人,压力大也许是一个原因,不管是来自于设计的,还是来自于自己的。我几乎没有时间停下来回顾,我所能做的只是不断催促着自己前进。逆水行舟,不进则退。     

Infrared brazing Ti-6Al-4V and SP-700 alloys using the Ti-20Zr-20Cu-20Ni braze alloy

Great efforts have been made in brazing high-strength α-β titanium alloys below their beta-phase transformation temperature in order to obtain optimized mechanical properties. The brazing temperature of the cold roll-bonded Ti-20Zr-20Cu-20Ni foil is roughly 70 °C lower than that of Ti-15Cu-15Ni filler metal. Moreover, the detrimental Cu-Ni and Cu-Ni-Zr rich Ti phases can be greatly reduced or eliminated by properly choosing the brazing thermal cycle. This research demonstrates the potential application of Ti-20Zr-20Cu-20Ni foil in brazing titanium alloys.     

Optical constants and electrical conductivity of Ge20Se60Sb20 thin films

Optical absorption and electrical resistivity of amorphous Ge₂₀Se₆₀Sb₂₀ films are investigated as a function of the thermal annealing. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation (h) = B(h–E_o)². Increasing the annealing temperature from 423 K to 553 K, decreases the optical gap of the film from 1.25 eV to 0.78 eV. The effect of annealing temperature on high frequency dielectric constant () and carrier concentration (N) was also studied. As a result of annealing the film at 533 K, the electrical resistivity and activation energy for conduction decreased from 5.7 × 10⁷ to 2.9 × 10² ·cm and from 0.94 to 0.34 eV, respectively. The crystalline structures resulting from heat treatment at different elevated temperatures have been studied by X-ray Diffraction (XRD). The optical and electrical changes were attributed to the amorphous-crystalline transformations in the chalcogenide films.