Effects of Cooling Rate and Component on the Microstructure and Mechanical Properties of Mg–Zn–Y Alloys

The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y(wt%) alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing(SDAS) of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates(Rc) from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0:45:45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction(Vf) of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.     

Effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers

In this paper, polyborosilazane precursor was synthesied from HMDZ, HSiCl₃, BCl₃ and CH₃NH₂ using a multistep method. By controlling the storage conditions, parts of the polyborosilazane fibers were hydrolyzed. FT-IR, NMR, XRD, TEM and monofilament tensile strength test were employed to study the effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers. FT-IR and NMR results indicate that Si-N group in PBSZ reacts with H₂O to form Si-O-Si group. After pyrolysis reaction at 1400℃, Si-O-Si group will finally transformed into highly ordered cristobalite and β-quartz, resulting in formation of the wrinkled surface of the obtained SiBN ceramic fiber. The strip-like defects on fiber surface, according to monofilament tensile strength test, had a significant effect on mechanical property of the obtained SiBN ceramic fiber and caused no increase in fiber tensile strength of hydrolytic polyborosilazane fiber before and after pyrolytic process.     

YSZ/MoS2 self-lubricating coating fabricated by thermal spraying and hydrothermal reaction

Thermal sprayed ceramic coatings have extensively been used in components to protect them against friction and wear. However, the poor lubricating ability severely limits their application. Herein, yttria-stabilized zirconia (YSZ)/MoS₂ composite coatings were successfully fabricated on steel substrate with the combination of thermal spraying technology and hydrothermal reaction. Results show that the synthetic MoS₂ powders are composed of numbers of ultra-thin sheets (about 7 ~ 8?nm), and the sheet has obvious lamellar structure. After vacuum impregnation and hydrothermal reaction, numbers of MoS₂ powders, look like flowers, generate inside the plasma sprayed YSZ coating. Moreover, the growing point of the MoS₂ flower is the intrinsic micro-pores of YSZ coating. The friction and wear tests under high vacuum environment indicate that the composite coating has an extremely long lifetime (>?100,000 cycles) and possesses a low friction coefficient less than 0.1, which is lower by about 0.15 times than that of YSZ coating. Meanwhile, the composite shows an extremely low wear rate (2.30?×?10^?7 mm³ N^?1 m^?1) and causes slight wear damage to the counterpart. The excellent lubricant and wear-resistant ability are attributed to the formation of MoS₂ transfer films and the ultra-smooth of the worn surfaces of hybrid coatings.     

复合材料在旋转压缩机上的应用分析

文章介绍了目前旋转式压缩机主要零部件的材料状况,详细论述了金属基复合材料、陶瓷基复合材料在旋转压缩机上的应用情况及前景,为复合材料在压缩机领域的应用提供指导。     

Theoretical Prediction of Chiral 3D Hybrid Organic–Inorganic Perovskites

Hybrid organic–inorganic perovskites (HOIPs), in particular 3D HOIPs, have demonstrated remarkable properties, including ultralong charge‐carrier diffusion lengths, high dielectric constants, low trap densities, tunable absorption and emission wavelengths, strong spin–orbit coupling, and large Rashba splitting. These superior properties have generated intensive research interest in HOIPs for high‐performance optoelectronics and spintronics. Here, 3D hybrid organic–inorganic perovskites that implant chirality through introducing the chiral methylammonium cation are demonstrated. Based on structural optimization, phonon spectra, formation energy, and ab initio molecular dynamics simulations, it is found that the chirality of the chiral cations can be successfully transferred to the framework of 3D HOIPs, and the resulting 3D chiral HOIPs are both kinetically and thermodynamically stable. Combining chirality with the impressive optical, electrical, and spintronic properties of 3D perovskites, 3D chiral perovskites is of great interest in the fields of piezoelectricity, pyroelectricity, ferroelectricity, topological quantum engineering, circularly polarized optoelectronics, and spintronics.     

A novel method based on convolutional neural networks for deriving standard 12-lead ECG from serial 3-lead ECG

Frontiers of Information Technology & Electronic Engineering - Reconstruction of a 12-lead electrocardiogram (ECG) from a serial 3-lead ECG has been researched in the past to satisfy the need...     

Structural,morphological, dielectric and magnetic properties of Zn-Zr co-doping yttrium iron garnet

In this study, yttrium iron garnet co-doped with Zn and Zr atoms with a chemical formula Y₃Zn_xZr_xFe_(5−2x)O₁₂ (x = 0.0-0.3) has been successfully prepared by the solid-state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y₃Zn_xZr_xFe_(5−2x)O₁₂ were investigated. The microstructure analysis indicates that co-doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO₂ appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co-doping method. Zn–Zr co-doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C).