Dry sliding wear of Ti-6Al-4V alloy in air and vacuum

1　INTRODUCTIONTitaniumanditsalloysareidealmaterialsforaerospaceandspaceindustriesbecauseoftheirhighspecificstrengthandexcellentcorrosionresistance[1] .Thevacuumenvironmentmustbeconsideredinspaceapplicationswherewearresistanceisrequired .Theabsorption ,stainsandoxidesmaybetotallyorpar tiallyremovedfromthesolidsurfaceinvacuum[2 ] .Thus ,arelativelyclearsurfacecanbeformed ,whichmightresultinanadhesionorevencoldweldingduetothestrongattractiveforcesbetweenmoleculesofthecontactingsurfaces[3] .…     

Synthesis and characterization of poly acrylic acid/graphite oxide nanocomposite

1　INTRODUCTIONOrganic intercalatedlayeredsolidshavebeenstudiedbyscientistsindifferentfieldsformanyyearsbecauseoftheirnew physicalandchemicalpropertiessuchaselectricalproperties[1] ,mechanicalproper ties ,thermalbehavior[2 ] ,surfaceandinterfacialproperties[3] .Graphiteoxide (GO)hasbeenstudiedformany years ,itsstructuralmodel[4 6 ] ,formationprocessandkinetics[7,8] havebeenstudiedindetail.IthasbeenreportedthatGOpossessesC OHande poxidefunctionalgroups[9] whichmakegraphiteox ideeasilyabs…     

ORTHOGONAL POLYNOMIAL EXPANSIONS OF THERMODYNAMIC PROPERTIES OF BINARY AND TERNARY SYSTEMS

1.IntroductionThereareseveralkindsofpolynomialexpansionsofthermodynamicproperties.FOrbinarysystemsthereareMargUlespolynomial[1],Redlich-Kisterpolynomial[2]andLegen-drepolynomialexpansions[3--5]etc..ForternaryandquaternarysystemsonlyMargulespolynomialexpansions[6'7]areawilable.Legendrepolynomialexpansionisbelievedtohavethead~agesofcoefficientsindependence[3--518]etc..ButwecanseethecoefficientsofLegendreexpansionsarenotcompletelyindependent,especiallywhentheinputdataarefleded.ThatisbecauseL…     

Measurement of surface crystallinity of PAA and PAANa coatings and its effect on hydrophilicity of coatings

1　INTRODUCTIONAsanimportantwater solublemacromoleculecompound,poly (acrylicacid) (PAA)anditssaltshavebeenwidelyused[1] .Utilizingitsfinefilm form ingcapacityandhydrophilicity ,Okoroaforetal[2 ] ,andPanetal[3] developedanewhydrophilicpaintforaluminiumfin[2 ,3] .Hydrophilic paintforheat ex changerofairconditioningdemandslittlesurfacecon tactangle ,sothatcontinuoushomogeneouswaterfilmcanformeasily ,andcandrainoffcondensedwa teronthesurfaceoffintimely[4 6 ] .Hydrophilicityofcoatingsisaffec…     

Synthesis and characterization of metastable Ag-B solid solutions

1　INTRODUCTIONMechanicalalloying (MA) [1] hasbecomeawide lyusedtechniquetosynthesizeavarietyofmaterials ,suchasamorphousalloys ,nanocrystallinematerials ,compounds ,solidsolutionsandsoforth .Especially ,theformationofnonequilibriummaterialscomposedofimmiscibleelementsbyMAhasreceivedincreasedattention .Anumberofbinarysystemshavebeenin vestigated ,includingAg Cu[2 4 ] ,Ag Fe[5] ,Fe Cu[6 ] ,Ag Ni[7] andothers .Comparisonwithothersynthesismethods ,suchasrapidlyquenching ,MAhasadvantages…     

Approximants in annealed IQC(Icosahedral Quasicrystal)-DQC(Decagonal Quasicrystal) pseudo-binary alloys

1　INTRODUCTIONWithnowadaysimprovementintheunderstand ingofthequasicrystallinematerial ,itspotentialap plicationshavebeengraduallypointedoutinvariousfieldsasthermalinsulation[1] ,lightabsorption[2 ,3] ,powergeneration[4 ] andhydrogenstorage[5,6 ] ,etc .Privatecompanieshaveshowngreatinterestespecial lyintheapplicationofitstribologyandthermo powergenerationproperties .Therefore ,betterunderstand ingofthescientificnaturesofquasicrystals (QCs)anditsapproximantisbelievedtobecomeagoodpaththatwi…     

Electrochemical characteristic of chemical-mechanical polishing of copper with oxide passive film

1　INTRODUCTIONThankstoitslowresistivityandhighelectromi grationresistance ,copperappearstobeaverypromisingsubstituteforaluminumininterconnec tions[1] .However ,copperisverydifficulttopattern ,andonlychemical mechanicalpolishing (CMP)tech nologycanresolvethisproblem[2 ] .CMPwasinitiallyinvestigatedandopenedoutfrom 1980soverseas[3] ,anditisthebestandonlyglobalplanarizationtech nologyatpresent ,butkeepsholdofbusinesssecretsallthetime .Fayolleetal[2 ] researchedCMPprocessofcopperwhereFe(…     

Phase transformation of nanocrystalline anatase powders during high energy planetary ball milling

1　INTRODUCTIONTitaniumdioxideisknowntoexistinthreecrys tallineformsofrutile ,anataseandbrookiteinnature .Rutileisthermodynamicallystablewhileanataseandbrookitecantransformirreversiblyandexothermicallytorutileoverarangeoftemperatures[1] .Inaddition ,therearetwohigh pressurephases ,srilankitewithorthorhombicstructureandTiO2 Ⅲ .Underhighpressure ,anataseandrutilecantransformtosri lankite[2 4 ] .Thesrilankitephasecantransformbacktorutileunderappropriateconditions[5] .Overthepastfew years …     

Synthesis and fluorescence properties of terbium-calcium-PMDMBA

1　INTRODUCTIONInrecentyears,manyinvestigationsonfluores cencepropertiesofrareearthions containingpolymercomplexeshavebeenmadebecausethepolymerscanbeusedasluminescenceandlasermaterialswithgoodquality[15] .Okamotoetal[6 8] synthesizedpolymerscontainingcoordinationgroupsandstudiedtheirfluo rescenceproperties .However ,thesynthesisoffunc tionalgroupspolymerswith goodenergydonerandenergylevelmatchingcapabilitywasverycomplicat ed ,whichmadetheuseofpolymerluminescentmate rialsuneconomic[1] .Fur…     

Cavitation erosion resistance and ratio of elastic deformation energy to total deformation energy for Ti_3Al and TiNiNb alloys

1　INTRODUCTIONCavitationerosioniscausedbythegrowthandcollapseofvaporcavitiesorbubblesduetolocalpres surefluctuationinaliquid[1] .Itisaseriousprobleminhigh speedcomponentsofhydraulicmachines .Al thoughagreatamountofworkonthecavitationphe nomenahasbeen published ,thecavitationerosionmechanismofmaterialsisstillnotunderstoodcom pletely .Itisgenerallybelieved[2 ,3] thatmechanicalattackisadominantmechanismforcavitationero sion .Manyinvestigations[4 6 ] attemptedtocorrelatethemechanicalproperti…     

行波磁场作用对凝固过程中气泡的影响

研究行波磁场对铝合金除气行为的影响,计算行波磁场对气泡形核临界半径的影响。结果表明：在行波磁场作用下,气泡的临界形核半径随着电磁场强度的增大呈线性递减,电磁力促进了气泡的非均匀形核,电磁力使得气泡在熔体中长大,并在电磁力的驱动下向熔体的外部溢出。试样中的气泡数随行波磁场感应强度的增大而减少。     

RETRACTED ARTICLE: Grain refinement of AA5754 aluminum alloy by ultrasonic cavitation: Experimental study and numerical simulation

In this work, an experimental investigation was carried out on the grain refinement of molten AA5754 Aluminum alloy through ultrasonic treatment. The cavitation induced heterogeneous nucleation was suggested as the major mechanism for grain refinement in the AA5754 aluminum alloy. A numerical simulation was performed to predict the formation, growth and collapse of cavitation bubbles in the molten AA5754 Aluminum alloy. Moreover, the acoustic pressure distribution and the induced acoustic streaming by ultrasonic horn reactor were investigated. It is suggested that the streaming by ultrasonic could transport the small bubbles formed in the ultrasonic cavitation zone into the bulk of melt rapidly. These micro-bubbles are collapsed due to acoustic vibrations where the resulting micro-jets are strong enough to break the oxide layer and to wet the impurities. These exogenous particles, intermetallics and oxides could contribute to the formation of fine, uniform and equiaxed microstructure across the treated melt. The experimental results confirmed the simulation predictions.     

GASAR和Gasarite研究进展

金属／气体共晶定向凝固(GASAR)是一种制备气孔定向排布的规则多孔金属(Gasarite)的新工艺。简要回顾了该工艺的原理和发展现状，介绍了由该工艺制备的规则多孔金属的结构和性能特点及其应用，同时介绍了从事该研究的一些进展。     

基底形貌及润湿性对表面异质形核的影响

采用化学刻蚀及氟硅烷修饰的方法,制备了具有不同粗糙程度及润湿特性的纯铝基底,将基底置于NH4Cl-70％H2O溶液中,以激冷的方式触发NH4Cl晶粒形核,并考察了基底形貌及润湿性对表面异质形核的影响规律和机制.结果表明,未修饰的粗糙纯铝基底表面与氯化铵晶胚之间的反应性润湿特性,使异质形核较易发生,随着粗糙度因子的增大,形核点增加;修饰后的粗糙基底表面覆有的氟硅烷抑制了反应性润湿特性,使异质形核不易发生,且随着粗糙度因子的增大,形核点减少.所观察到的实验现象与基于Wenzel模型的粗糙基底异质形核分析结论有较好的吻合.     

Effect of substrate micro-morphology on heterogeneous nucleation

The heterogeneous nucleation process of NH4Cl crystals from a NH4Cl-70wt.%H2O solution on rough chilling substrates was considered in this paper. Scratched and etched substrates of aluminum were prepared with different surface morphologies. It was concluded that for nucleation to occur on a rough substrate surface, the wettability or the generally said roughness are not the key factors affecting the heterogeneous nucleation process. Rather the surface morphologies on the nanometer scale, which is close to the scale of the critical nucleation radius, are more important.     

Melt conditioning by advanced shear technology (MCAST) for refining solidification microstructures

Abstract

MCAST (melt conditioning by advanced shear technology) is a novel processing technology developed recently for conditioning liquid metal prior to solidification processing. The MCAST process uses a twin screw mechanism to impose a high shear rate and a high intensity of turbulence on the liquid metal, so that the conditioned liquid metal has uniform temperature, uniform chemical composition and well-dispersed and completely wetted oxide particles with a fine size and a narrow size distribution. The microstructural refinement is achieved through an enhanced heterogeneous nucleation rate and an increased nuclei survival rate during the subsequent solidification processing. In this paper we present the MCAST process and its applications for microstructural refinement in both shape casting and continuous casting of light alloys.     

Oxidation resistance of graphene-coated molybdenum: Effects of pre-washing and hydrogen flow rate

An effective approach to protect metal surfaces against oxidation and corrosion is of great importance for various practical and industrial applications. Current solutions, however, typically introduce several undesired effects, including increased thickness and changes in the metal's physical properties. Here, we demonstrate the formation of a graphene coating using an atmospheric pressure chemical vapor deposition (APCVD) technique combined with a specifically tuned hydrogen flow rate (200, 500, and 1000 sccm) and an acid solution for pre-washing. The pre-washing process consists of acid etching by three different acids that help to remove impurities. These impurities include native molybdenum oxide and impurities that can act as nucleation centers for multilayer graphene. The specimens were characterized by Raman spectroscopy, optical microscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Results indicate that the molybdenum surface was well protected from oxidation, even after heating to a temperature of 300 °C in air for 2 h.     

Heat transfer and grain refining mechanism during melt treatment by cooling sloping plate

Heat transfer of flow melt and grain refining mechanism during melt treatment by the cooling sloping plate were investigated.The results show that the cooling sloping plate can refine not only grains of alloys but also can obviously refine pure metal.Cooling ability of the plate is the key factor that induces grain refining,the plate material and the flow amount can affect cooling rate of the melt and thus affect refining effectiveness.The cooling rate of the melt on the cooling sloping plate is much faster than that of the conventional casting process,which can reach 1000 K/s and belongs to meta-rapid solidification scope.The thickness of the temperature boundary layer is much larger than that of the velocity boundary layer on the sloping plate,but the temperature gradient is small in the temperature boundary layer.Under strong cooling action by the cooling plate,most parts of the melt on the plate surface can form undercooling,which causes continuous eruptive nucleation,this is the main grain refining mechanism,and the heterogeneous nucleation on the plate surface is a helpful supplement for the nucleation.     

The mechanism of initial de-wetting and detachment of thin Au films on YSZ

Thin Au layers on single crystal Y₂O₃-doped ZrO₂ (YSZ) de-wet from the substrate during thermal annealing in the solid state, and form small crystalline particles. Voids in the film nucleate at the metal–ceramic interface, and then grow to form pinholes in the film. Thus void nucleation at the metal–ceramic interface was identified to be the mechanism for solid-state de-wetting, rather than grain boundary grooving at the free surface of the film. Eventually, complete de-wetting occurs via solid-state diffusion, driven by minimization of the surface and interface energies of the system. In parallel to the de-wetting process, bubbles form in the film, driven by compressive thermal stresses and by the pressure exerted by gas chemisorbed from the substrate.     

H, O,P,S和N对金属Ni塑性形变机制影响的第一性原理研究

本文基于密度泛函理论研究了H、O、P、S和N杂质以间隙式固溶于Ni(111)后对其变形能力的影响。发现：S、P在晶粒内部不稳定，不易存在于Ni(111)的间隙位置，而易向界面和表面扩散，H、O和N可在晶内分布，且N在Ni晶内分布的倾向性较大。对于Ni (111)<112>滑移系，P使得Ni层错能增大，而H、N、O、S降低了Ni的层错能，即H、N、O、S固溶于Ni使其沿(111)<112>滑移更为容易。总体来看，当外部环境介质H、N、O侵入到Ni基体时，由于使得体系的层错能降低，除产生的氧化、腐蚀等作用外，还使得该区域抵抗变形的能力下降，增大了蠕变变形的可能性。