Magnesium matrix composite reinforced by nanoparticles-A review

Significant progress has been made in magnesium-based composites during recent decades,especially for the appearance of magnesium matrix composite reinforced by nanoparticles.The nanoparticles added not only exhibit a good strengthening effect,but also maintain the initial toughness of the matrix,effectively balancing the contradiction between the strength and plasticity in the traditional magnesium matrix composites.The magnesium matrix nanocomposites with excellent mechanical properties have pushed the development of magnesium matrix composites to a new stage.However,it is very difficult to disperse the nanoparticles in metal melt especially in magnesium melt which is different from other metal melts and dangerous during the cast processing.This means that the preparation of magnesium matrix nanocomposite is extremely challenging.Further,the magnesium matrix nanocomposites possess a distinctive characteristic in deformation behavior,strengthening and toughening mechanism due to their special size effect of nanoparticles.Accordingly,this review will focus on the new preparation technologies,deformation behavior,mechanical properties and strengthening and toughening mechanisms.The potential applications,development trends and future research ideas of magnesium matrix nanocomposite are also prospected.©2020 Published by Elsevier B.V.on behalf of Chongqing University.

Effects of Organic and Chemical Fertilizations and Microbe Inoculation on Physiology and Growth of Sweet Corn Plants

A pot culture experiment was carried out in a glasshouse to compare the physiology and growth of sweet corn plants (Zea mays L. cv. Honey Bantam) grown under organic and chemical fertilizations with or without microbial inoculation (MI). The organic fertilizer used was fermented mainly using rice bran and oil mill sludge, and the MI was a liquid product containing many beneficial microbes such as lactic acid bacteria, yeast, photosynthetic bacteria and actinomycetes. The application amounts of the organic fertilizer and chemical fertilizers were based on the same rate of nitrogen, phosphorus and potassium. Sweet corn plants fertilized with organic materials inoculated with beneficial microbes grew better than those without inoculation. There were no significant differences in physiology and growth of the sweet corn plants between treatments of chemical fertilizers with and without MI. Among the organic fertilization treatments, only the sweet corn plants with organic fertilizer and MI applied 4 weeks before sowing had similar photosynthetic capacityj total dry matter yield and ear yield to those with chemical fertilizers. Sweet corn plants in other organic fertilization treatments were weaker in physiology and growth than those in chemical fertilization treatments. There was no significant variance among chemical fertilization treatments at different time. It is concluded from this research that this organic fertilizer would be more effective if it was inoculated with the beneficial microbes. Early application of the organic fertilizer with beneficial microbes before sowing was recommended to make the nutrients available before the rapid growth at the early stage and obtain a yield similar to or higher than that with chemical fertilizations.

Microstructure and room temperature tensile properties of 1μm-SiCp/AZ31B magnesium matrix composite

In the present study,AZ31B magnesium matrix composites reinforced with two volume fractions(3 and 5 vol.%)of micron-SiC particles(1μm)were fabricated by semisolid stirring assisted ultrasonic vibration method.The as-cast ingots were extruded at 350℃ with the extrusion ratio of 15:1 at a constant ram speed of 15 mm/s.The microstructure of the composites was investigated by optical microscopy,scanning electron microscope and transmission electron microscope.Microstructure characterization of the composites showed relative uniform reinforcement distribution and significant grain refinement.The presence of 1μm-SiC particles assisted in improving the elastic modulus and tensile strength.The ultimate tensile strength and yield strength of the 5 vol.%SiCp/AZ31B composites were simultaneously improved.

SUBSTRATE MATERIALS FOR POLY-CSiTF SOLAR CELLS: OPTIMIZATION OF SILICON SHEET FROM POWDER

The optimization of silicon sheet from powder (SSP) technology as polycrystalli ne silicon thin film (poly-CSiTF) solar cells' substrate materials is studied by orthogonal design experimental method. Based on technological optimization of S SP prepared from electronic grade silicon powder, SSP solar cell devices with si mple structure are prepared and the effect of SSP substrate is discussed. Up to now, the conversion efficiency of the prepared solar cells on low purity SSP sub strate with fundamental structure has reached 8.25% (with area of 1cm×1cm).

Amplitude analysis of the decays D^(0)→π^(+)π^(−)π^(+)π^(−)and D^(0)→π^(+)π^(−)π^(0)π^(0)

Using e^(+)e^(−)annihilation data corresponding to an integrated luminosity of 2.93 fb^(−1)taken at the center-of-mass energy√s=3.773 GeV with the BESIII detector,a joint amplitude analysis is performed on the decays D^(0)→π^(+)π^(−)π^(+)π^(−)and D^(0)→π^(+)π^(−)π^(0)π^(0)(non-η).The fit fractions of individual components are obtained,and large interferences among the dominant components of the decays D^(0)→a_(1)(1260)π,D^(0)→π(1300)π,D^(0)→ρ(770)ρ(770),and D^(0)→2(ππ)_(S)are observed in both channels.With the obtained amplitude model,the CP-even fractions of D^(0)→π^(+)π^(−)π^(+)π^(−)and D^(0)→π^(+)π^(−)π^(0)π^(0)(non-η)are determined to be(75.2±1.1_(stat).±1.5_(syst.))%and(68.9±1.5_(stat).±2.4_(syst.))%,respectively.The branching fractions of D^(0)→π^(+)π^(−)π^(+)π^(−)and D^(0)→π^(+)π^(−)π^(0)π^(0)(non-η)are measured to be(0.688±0.010_(stat.)±0.010_(syst.))%and(0.951±0.025_(stat.)±0.021_(syst.))%,respectively.The amplitude analysis provides an important model for the binning strategy in measuring the strong phase parameters of D^(0)→4πwhen used to determine the CKM angleγ(ϕ_(3))via the B^(−)→DK^(−)decay.

Determination of the number ofψ(3686)events taken at BESⅢ

The number ofψ(3686)events collected by the BESⅢdetector during the 2021 run period is determined to be(2259.3±11.1)×10~6 by counting inclusiveψ(3686)hadronic events.The uncertainty is systematic and the statistical uncertainty is negligible.Meanwhile,the numbers ofψ(3686)events collected during the 2009 and 2012run periods are updated to be(107.7±0.6)×10~6 and(345.4±2.6)×10~6,respectively.Both numbers are consistent with the previous measurements within one standard deviation.The total number ofψ(3686)events in the three data samples is(2712.4±14.3)×10~6.

Processing, Microstructure and Mechanical Properties of Ti6Al4V Particles-Reinforced Mg Matrix Composites

Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of the ingots. Furthermore, the optimal speed of the heating and the liquid stirring could overcome particle settlement caused by the density difference between the matrix and the particles. Ti6Al4V particles distributed uniformly in the composites with different particle contents. The average grain size decreased with the increase in the particle contents. The Ti6A14V particles bonded pretty well with the alloy matrix. In addition, there were some interfacial reactions in the composites. There were rod-like A13Ti phases at the interface. The precipitates extended from the particle surface to the matrix, and they might improve the interfacial bonding strength. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased, and the elongation was much better than that of the same matrix material reinforced with SiC particles. Thus, the novel composites exhibit better comprehensive mechanical properties.

Effect of forced-air cooling on the microstructure and age-hardening response of extruded Mg-Gd-Y-Zn-Zr alloy full with LPSO lamella

The homogenized Mg-8.2 Gd-3.8 Y-1.0 Zn-0.4 Zr(wt.%)alloy full of plate-shaped long period stacking ordered(LPSO)phases was hot extruded in the atmosphere and cooled by the forced-air,then the effect of forced-air cooling on the microstructure and age-hardening response of the alloy was investigated in this work.The results show that in comparison with the extruded sample cooling in the atmosphere,the forced-air cooling restricts dynamic recrystallization(DRX)and brings about finer dynamic recrystallized(DRXed)grain size,stronger basal texture and higher dislocation density.Furthermore,the forced-air cooling promotes the dynamic precipitation in the DRXed regions and facilitates formation of plate-shaped LPSO phases andγ’phases with smaller interspacing in the unrecrystallized(un DRXed)regions,then slightly restricts the precipitation ofβphases during aging.After peak-ageing treatment,the extruded sample with forced-air cooling shows superior tensile properties with a tensile yield strength of 439 MPa,an ultimate tensile strength of 493 MPa,and elongation to failure of 18.6%.

Observation of the Crab Nebula with LHAASO-KM2A−a performance study

A sub-array of the Large High Altitude Air Shower Observatory(LHAASO),KM2A is mainly designed to observe a large fraction of the northern sky to hunt for γ-ray sources at energies above 10 TeV.Even though the detector construction is still underway,half of the KM2A array has been operating stably since the end of 2019.In this paper,we present the KM2A data analysis pipeline and the first observation of the Crab Nebula,a standard candle in very high energy γ-ray astronomy.We detect γ-ray signals from the Crab Nebula in both energy ranges of 10-100 TeV and>100 TeV with high significance,by analyzing the KM2A data of 136 live days between December 2019 and May 2020.With the observations,we test the detector performance,including angular resolution,pointing accuracy and cosmic-ray background rejection power.The energy spectrum of the Crab Nebula in the energy range 10-250 TeV fits well with a single power-law function dN/dE=(1.13±0.05stat±0.08sys)×10^(-14).(E/20 TeV)-309±0.06stat±0.02syscm^(-2) s^(-1) TeV^(-1).It is consistent with previous measurements by other experiments.This opens a new window of γ-ray astronomy above 0.1 PeV through which new ultrahigh-energy γ-ray phenomena,such as cosmic PeVatrons,might be discovered.

Effect of environments and normal loads on tribological properties of nitrided Ni(45)(FeCoCr)(40)(AlTi)(15)high-entropy alloys

The tribological properties of nitrided Ni(45)(FeCoCr)(40)(AlTi)(15)high-entropy alloys(HEAs)were investigated in air and simulated acid rain under different normal loads(5,7,10,and 12 N)at ambient temperature.The results revealed that as-cast HEAs were only composed of FCC phase,while the volume fraction of FCC phase in the nitrided alloys was significantly reduced.Moreover,the hard phases of AIN,CrN,Fe4 N,and TiN phases were formed in the nitrided alloys.The thickness of the nitriding layer was about 8.4μm.The hardness increased from 8.7 GPa in as-cast alloys to 14.5 GPa in the nitrided alloys.In addition,under the same conditions,the friction coefficient of the nitrided alloys was higher than that of as-cast alloys,but the wear rate was generally lower than that of as-cast alloys.Furthermore,the wear rate of the nitrided alloys was the lowest in acid rain due to the lubrication,cleaning,and cooling in the liquid environment.In air,dominating wear mechanisms in as-cast and nitrided alloys were abrasive,delamination,and adhesive wears.And,the wear mechanism of as-cast and nitrided alloys in acid rain was mainly abrasive and corrosion wears.

Performance of LHAASO-WCDA and observation of the Crab Nebula as a standard candle

The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.

A Novel Melt Processing for Mg Matrix Composites Reinforced by Multiwalled Carbon Nanotubes

Carbon nanotubes（CNTs） reinforced Mg matrix composites were fabricated by a novel melt processing.The novel processing consisted of two courses：CNTs pre-dispersion and ultrasonic melt processing.Mechanical ball-milling was employed to pre-disperse CNTs on Zinc（Zn） flakes.Serious CNT entanglements were well dispersed to single CNT or tiny clusters on Zn flakes.The ultrasonic melt processing further dispersed CNTs in the Mg melt,especially tiny CNT clusters.Thus,a uniform dispersion of CNTs was achieved in the as-cast composites.Hot extrusion further improved the distribution of CNTs.CNTs increased both the strength and elongation of the matrix alloy.Notably,the elongation of the matrix alloy was enhanced by 40%.Grain refinement and the pulling-out of CNTs resulted in the evident improvement of ductility for the composites.

Geometrical reconstruction of fluorescence events observed by the LHAASO experiment

The LHAASO-WFCTA experiment,which aims to observe cosmic rays in the sub-EeV range using the fluorescence technique,uses a new generation of high-performance telescopes.To ensure that the experiment has ex-cellent detection capability associated with the measurement of the energy spectrum,the primary composition of cosmic rays,and so on,an accurate geometrical reconstruction of air-shower events is fundamental.This paper de-scribes the development and testing of geometrical reconstruction for stereo viewed events using the WFCTA(Wide Field of view Cherenkov/Fluorescence Telescope Array)detectors.Two approaches,which take full advantage ofthe WFCTA detectors.are investigated.One is the stereo-angular method,which uses the pointing of triggered SiPMs in the shower trajectory,and the other is the stereo-timing method,which uses the triggering time of the fired SiPMs.The results show that both methods have good geometrical resolution:the resolution of the stereo-timing method is slightly better than the stereo-angular method because the resolution of the latter is slightly limited by the shower track length.

Bulk nanocrystalline W-Ti alloys with exceptional mechanical properties and thermal stability

Nanocrystalline(NC)W metals and alloys often exhibit higher radiation tolerance and strength than their coarse-grained counterparts.However,their thermal stability is low,making it difficult to achieve bulk NC W metals and alloys by consolidation using conventional techniques such as pressure-less sintering,hot-explosive-compaction sintering,and spark plasma sintering.Here we report the synthesis and mechanical properties of bulk NC W_(100-x)Ti_(x)(x=10 at.%-30 at.%)alloys prepared by consolidating mechanically alloyed NC powders under a high-temperature/high-pressure condition.Adding 20 at.%-30 at.%Ti largely improves the sinterability of NC W-Ti alloy powders.The room-temperature microhardness and compressive yield strength of consolidated bulk NC W_(80)Ti_(20) alloy are∼16.9 and 6.0 GPa,respectively,which are mainly caused by grain boundary strengthening and significantly higher than those of previously reported W and W alloys.The ultimate compressive strength of bulk NC W_(80)Ti_(20) measured between 900 and 1100°C deceases with increasing temperature.This behavior can be explained by the activation of Rachinger grain boundary sliding.No grain growth is observed in bulk NC W_(80)Ti_(20) after compression at 1000°C.Theoretical calculation suggests that it is the segregation of Ti at grain boundaries that decreases the specific grain boundary free energy and makes the NC W_(80)Ti_(20) alloy thermodynamically stable.

A dynamic range extension system for LHAASOWCDA-1

Purpose The main scientific goal of LHAASO-WCDA is to survey gamma-ray sources with energy from 100 GeV to 30 TeV.To observe high-energy shower events,especially to measure the energy spectrum of cosmic rays from 100 TeV to 10 PeV,a dynamic range extension system(WCDA++)is designed to use a 1.5-inch PMT with a dynamic range of four orders of magnitude for each cell in WCDA-1.Method The dynamic range is extended by using these PMTs to measure the effective charge density in the core region of air shower events,which is an important parameter for identifying the composition of primary particles.Result and Conclusion The system has been running for more than one year.In this paper,the details of the design and performance of WCDA++are presented.

Prospects for a multi-TeV gamma-ray sky survey with the LHAASO water Cherenkov detector array

The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. WCDA is aimed at the study of TeV γ-rays. In order to evaluate the prospects of searching for TeV γ-ray sources with WCDA, we present a projection of the one-year sensitivity of WCDA to TeV γ-ray sources from TeVCat using an all-sky approach. Out of 128 TeVCat sources observable by WCDA up to a zenith angle of 45°, we estimate that 42 would be detectable in one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei(AGN).