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| 1 | Current understanding of the origin of equiaxed grains in pure metals during ultrasonic solidification and a comparison of grain formation processes with low frequency vibration,pulsed magnetic and electric-current pulse techniques显示文摘The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(i.e.independent of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electric current pulse techniques.The dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites(ultrasonic field),wall crystals arising from the cold surface of the mould(electric current pulse,magnetic and pulsed magnetic fields).In all these cases fluid flow provides an additional contribution(e.g.reduced temperature gradients,growth rate and remelting of dendrites)to maintaining an equiaxed grain structure.The origin of equiaxed grains under an external field also depends on the casting conditions(volume and shape of casting)and the type of alloy other than the mechanisms specific to a particular technique.The current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals(magnesium and zinc)subjected to Ultra Sonic Treatment(UST).The role of the temperature range of UST application,time duration and an unpreheated sonotrode are examined with respect to the origin,evolution of equiaxed grain structure,morphology and the columnar to equiaxed transition.The origin of grains was analysed from three fundamental aspects that contribute to refinement(i)heterogeneous nucleation(ii)fragmentation of existing dendrites and(iii)grains produced from the colder surfaces(arising from mould walls or vibrating surfaces as wall crystals).A comparison of UST refinement with mechanical,low-frequency vibration,electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces(sonotrode and mould wall)in influencing grain refinement. | Nagasivamuni Balasubramani Gui Wang David H.St John Matthew S.Dargusch | 2021 | Journal of Materials Science & Technology2021，，6： | 5 |
| 2 | A comparative study of the role of solute,potent particles and ultrasonic treatment during solidification of pure Mg,Mg-Zn and Mg-Zr alloys显示文摘Ultrasonic treatment(UST)applied during the solidification of pure Mg,eutectic(Mg-Zn)and peritectic(Mg-Zr)alloys was investigated in order to explore the grain refinement mechanisms.Temperature dependent grain refinement is observed in pure Mg where decreasing the superheat temperature(at which UST is applied from above the melting temperature,TM)from 100℃to 40℃produces significant refinement with a uniform grain structure.The presence of solute reduces the temperature dependence of the UST refinement and excellent grain refinement is obtained regardless of the superheat temperature(100℃or 40℃)and even with the use of preheated sonotrode in the Mg-6 wt.%Zn alloy.A further improvement in grain refinement is achieved when the alloy contains potent particles that introduce additional nucleation of grains in Mg-0.5 and 1.0 wt.%Zr alloys(producing an average grain size of≤100μm).At 40℃superheat,UST of Mg-Zn alloys produces excellent refinement(average grain size<200μm)with non-dendritic grains,which is normally achieved only with the addition of grain refining master alloy in the as-cast condition.The enhanced refinement observed in the eutectic alloy is explained through the undercooling imposed by a relatively cold sonotrode combined with high frequency vibrations and acoustic streaming.The advantages of using a cold sonotrode,a low superheat and solute are demonstrated for achieving significant refinement during solidification of Mg alloys under UST without or with a lower addition of grain refining master alloys. | Nagasivamuni Balasubramani Gui Wang Mark A.Easton David H.St John Matthew S.Dargusch | 2021 | Journal of Magnesium and Alloys2021，9，3： | 4 |
| 3 | 混凝土高拱坝设计中必须考虑的问题(摘译)显示文摘混凝土高拱坝的大部分问题都出现在拱座。本文拟从以下几个方面来分析这一区域的应力和变形。 | H.Stuble R.Windmann 高健 | 1997 | 浙江水利水电专科学校学报1997，0，1： | 2 |
| 4 | Softwood hemicellulose-degrading en-zymes from Aspergillus niger:purification and properties of a _-man-nanase显示文摘 | Ademark P A. Varga J. Medve V.Harjunpaa T.Drakenberg F.Tjerneld H.St?lbrand | | 0，，： | 1 |
| 5 | John's Wort (hypericum perforatum)a herbal antidepressant显示文摘 | Hippius H.st | | 0，，03： | 1 |
| 6 | 在RHIC和LHC能区双喷注诱发的马赫锥:大爆炸物质的声速(英文)显示文摘A study of Mach shocks generated by fast partonic jets propagating through the quark-gluon plasma(QGP)is reviewed briefly.We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies compared to those created by a jet propagation through a static medium. Moreover,a new hydrodynamical study of jet energy loss is presented. | B.Betz P.Rau H.Stcker | 2007 | 高能物理与核物理2007，31，12： | 0 |
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