Improving fatigue property of Al-Li alloy by thermo-mechanical treatment

1　INTRODUCTIONAl Lialloyhasbeenusedwidelyasakindofnewstructuralspaceflightmaterialdependingonitshighstrengthandlowdensity[1,2 ] .ManyresearchworkshavebeendoneonAl Lialloy[36 ] ,butfewofthemareaboutfatiguefaliure .Becausemorethan 80 %ofstructuralmaterials failuresarecausedbythefatiguefailuresdirectlyorindirectly[7,8] ,itisnecessarytostudythefatiguepropertyofAl Lialloy[911] .ThereisobviousageingstrengtheningeffectwhenAl Lialloyisagedbelowthesolubilitycurveoftransientphaseδ′ .However,t…     

Effect of heat-treatment on fatigue property of Al-Li alloy

1　INTRODUCTIONMorethan 80 %ofstructuralmaterials failuresarecausedbyfatiguefailuredirectlyorindirectly [1,2 ] .Al Lialloyhasbeenusedasakindofnewstructuralspaceflightmaterialbecauseofitshighstrengthandlowdensity[3,4 ] .AlthoughalotofresearchesaboutAl Lialloy[58] havebeendoneinthepastfew years ,thede tailedstudyonthefatigueproperty[910 ] hasnotbeendonesomuch .Especially ,therewaslittleresearchonthefatiguecrackinitiatingandpropagatingbehavior.Be causethestrengthofAl Lialloycouldbeaffected…     

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…     

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…     

Development of cube texture in multistage annealing of high purity aluminum foils

1　INTRODUCTIONThecubetextureisimportanttohighpurityalu minumfoilsforhighvoltagecapacitorsbecauseitcanenlargeeffectivesurfaceofaluminumfoilsandin creasecapacitancethroughchanneletching .Inordertoincreasethevolumefractionofthecubecompo nent ,a greatdealofresearchesontheformationmechanismofcubetexturehavebeendone ,andmanymethodswere proposed ,suchasimpuritycontrol ling[1,2 ] ,directionalsolidification[3] ,preheating[4 ] ,inhomogeneousrolling[5] ,vacuumannealing[6 ] andsoon .Inthispaperamulti…     

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

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

ORTHOGONAL POLYNOMIAL EXPANSIONS OF THERMODYNAMICPROPERTIES 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…     

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…     

Preparation of Ir/IrO_x pH electrode based on melt-oxidation and its response mechanism investigation

1　INTRODUCTIONMetaloxideswereregardedasthealternativestoconventionalglasselectrode .VariousmetaloxideshavebeensuggestedaspHsensingelectrode ,suchasMnO2 ,PbO2 ,Co3O4 ,TiO2 ,PtO2 ,RuO2 ,RhO2 ,OsO2 ,IrO2 [16 ] .Amongthelargenumberofthereportedmateri als ,iridiumoxideistheoneofthemostpossiblecan didatesforsuchapplication[2 ] ,anditcanbepreparedbyseveralmethods ,suchaselectrochemicaloxida tion[7] ,sputtering[8] ,thermaloxidization[913] .Al thoughIrOxisoneofthebestmetaloxideforpHsensi…     

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(…     

SEM observation of gibbsite precipitation with seeds from sodium aluminate solutions promoted by ultrasound

1　INTRODUCTIONThemechanismofgibbsiteprecipitationfromsodiumaluminatesolutionsshowsthatthephysicalchemistrypro cessofthedecompositionarecontactedwiththequalityandmorphologyofAl(OH) 3seeds.Especially ,theinter actionbetweenthesurfaceofseedsandliquorisprovedtobeveryimportanttothemicromechanismofthedecom position .Leeetal[13] foundthatgibbsitesinglecrystalgrowthhavethreedifferentshapes :diamondshaped ,hexagonandelongatedhexagon (Fig .1) ,andeachhasseparategrowthrate .Onthesameexperimentcond…     

铜模内径对亚快速凝固K424合金析出相的影响

采用阶梯铜模喷铸制备了不同内径的亚快速凝固K424合金,采用时效处理研究了原始非平衡组织状态对快冷合金γ′析出相析出的影响。结果表明:铜模内径的降低可以减弱合金凝固过程中的溶质偏析程度,缩短相变时间,抑制共晶相及析出相形成,有利于获得高固溶组织。经700℃时效30 min处理后,Ф2合金由于形核驱动力高,临界形核半径小,相比Ф6合金优先析出γ′相。当时效温度提高到800℃,低内径铜模基体中可形成均匀分布的析出相,同时形核密度得到显著提高。随时效时间延长,γ′相先快速长大随后缓慢生长,其中Ф2合金由于γ′相过早析出导致其尺寸比相应的Ф6合金更大。析出相析出可以有效增加合金的显微硬度,经800℃时效180 min后Ф2合金硬度高达494 HV0.2,相比原始快冷合金提高13.8%。     

直轧条件下含Nb钢筋中Nb(C,N)的析出强化机理及控冷工艺优化

为了解决方坯直轧工艺生产含Nb钢筋出现的强化效果不显著问题,通过经典形核理论计算了Nb(C, N)在奥氏体中沉淀析出动力学行为特点,并通过现场控冷工艺试验验证了理论计算的结果。结果表明,加热炉轧制生产含Nb钢筋过程中Nb(C, N)的沉淀析出以晶界形核为主,方坯直轧工艺生产含Nb钢筋过程中Nb(C, N)的沉淀析出以位错形核为主;在含Nb钢筋的成分体系下,Nb(C, N)在奥氏体中沉淀析出过程中的晶界形核和位错形核C曲线鼻尖点温度分别约为1000 ℃和900 ℃;方坯直轧工艺生产含Nb钢筋可以在精轧机架间设置多段预穿水,以保证足够低的终轧温度,来获得Nb(C, N)沉淀析出的最佳强化效果。     

变形条件和冷却速率对低碳含Nb钢的相变及纳米析出的影响

利用Gleeble 3800热模拟试验机,研究了奥氏体再结晶和未再结晶组织对低碳含Nb钢连续冷却转变行为的影响,并对不同变形温度及冷却速率下Nb(C, N)的纳米析出行为进行了研究。结果表明,未再结晶区奥氏体的变形能够为多边形铁素体提供更多的相变形核点,扩大铁素体相变区,并且能够细化铁素体晶粒;相比于再结晶区1050℃单道次变形,未再结晶区的第二道次变形能够促进Nb(C, N)的析出,其中910℃变形时Nb(C, N)的析出量最多,850℃次之;冷却速率的增大能够抑制Nb(C, N)在奥氏体中的析出,但能够促进其在铁素体中析出;对于本试验钢,10℃/s的冷却速率即可抑制Nb(C, N)的析出;Nb(C, N)的析出粒子平均粒径随着冷却速率的增加而减小。     

细化剂与冷却方式对K438合金组织和高温性能的影响

采用模壳面层细化与风冷/空冷相结合,研究了熔模精铸K438合金凝固组织及沉淀相形成规律,提出了改善合金高温力学性能的途径。结果表明,模壳面层细化为凝固过程提供了有效形核质点,促进凝固组织从柱状晶向等轴晶发生转变,有效地细化了合金的晶粒组织。风冷方式抑制了枝晶熟化和沉淀相粗化,显著降低二次枝晶间距及γ′析出相尺寸。截面等轴晶比例的增加有利于提高合金980℃/150 MPa高温持久性能。枝晶组织的细化及细小沉淀相的形成可以改善合金650℃高温拉伸强度,其中风冷试棒的高温屈服强度和伸长率分别为734 MPa和11%,相比空冷态分别提高了5%和41%。     

2507超级双相不锈钢中第二相的析出行为

利用OM、SEM和EBSD等研究了经1100 ℃保温30 min固溶的热轧超级双相不锈钢(SDSS)2507在不同时效温度(750~1000 ℃)及时间(1~240 min)下的第二相析出行为。结果表明,固溶态SDSS 2507的微观组织主要是铁素体和奥氏体。在750～1000 ℃时效处理后有σ相和χ相析出。时效温度较低时,χ相从铁素体相析出且稳定存在。随着时效温度的升高,σ相主要通过α→σ+γ₂共析反应生成,随着时效时间的延长,组织中亚稳态χ相溶解并促进σ相析出。另外,时效温度也会影响第二相形貌:高温时效时(＞950 ℃),析出相形貌主要为片状σ相和γ₂相,低温时效时析出物主要呈颗粒状。由第二相析出行为及第二相的TTT曲线可知,热轧变形使SDSS 2507第二相形核的孕育期缩短,析出速度提高,析出敏感温度约为950 ℃。     

热处理工艺参数对Cr8冷作模具钢组织和性能的影响

针对Cr8冷作模具钢的二次硬化问题,采用金相显微镜、SEM、EDS和洛氏硬度计,研究了低温回火和高温回火对Cr8冷作模具钢材料组织和性能的影响。结果表明,原材料组织为珠光体和少量长为9~41μm、宽为2~11μm大颗粒共晶碳化物;不同回火温度下,材料的组织为马氏体和少量长为4~25μm、宽为1~8μm的大颗粒共晶碳化物及细小二次析出碳化物;经1030℃淬火、高温520℃回火之后材料出现二次硬化现象,硬度为58. 4 HRC,比低温200℃回火下的硬度高出1. 4 HRC。Cr8钢的二次硬化是由于高温520℃回火之后,二次纳米级小颗粒碳化物析出较多,且颗粒均匀弥散分布于基体中造成的。     

形变及冷却速率对热轧超高强汽车钢板中纳米析出的影响

为精确控制热轧780 MPa级Nb-Ti微合金化C-Mn钢中的纳米析出物(Nb,Ti)C,利用热力模拟实验技水,通过透射电镜观察及统计分析,研究形变及冷却速率对纳米析出的影响规律.结果表明,形变可显著地提高析出物形核率,并细化析出物平均直径;析出物数量随冷却速率的增大逐渐减小;既定的实验条件下,冷却速率达到15℃/s可完全抑制析出物在冷却过程中形核;随着冷却速率的增大,析出物的形核区间由奥氏体区形核向铁素体或贝氏区转变,析出物平均直径明显细化;在低冷却速率条件下的变形实验钢中,形变提高组织中的空位浓度,促进析出物空位形核的发生;晶界或亚晶界是过饱和空位的主要陷阱,但空位的扩散活性很高致使低冷却速率条件下晶界或亚晶界附近的空位浓度低于析出物形核的临界形核浓度,从而无法形核,形成晶界附近无析出带;无析出带宽度随冷却速率的增大而减小,这归因于空位扩散活力随冷却速率的增大而降低.     

含钪7xxx系铝合金的再结晶

采用金相显微镜和透射电子显微镜研究了含钪Al-Zn-Mg-Cu-Zr系铝合金组织的再结晶,测试了不同温度下退火1h合金的硬度。结果表明:含0.20%Sc的7xxx系铝合金(冷变形量50%)的再结晶起始温度为475℃,再结晶终了温度为525℃。合金在均匀化以及热加工过程中析出细小、弥散的二次A l3(Sc,Zr)粒子钉扎位错、亚晶界和晶界,使回复过程中的位错运动受阻,保持基体内较高的位错的密度,阻碍加热时位错重新排列呈亚晶界以及更进一步发展成大角度晶界的过程;阻碍了再结晶核心长大过程,阻碍大角度晶界的迁移,从而提高再结晶温度。     

等温变形0Cr14Mn21NiN无磁不锈钢的晶间腐蚀敏感性

通过Thermal-Calc热力学软件对0Cr14Mn21NiN无磁不锈钢中碳化物析出的平衡相区进行了计算,并通过时效处理试验进行了验证。通过不同参数的等温变形试验对实际的非平衡态碳化物析出行为进行了研究。通过双环电化学动电位再活化法(DL-EPR)对等温变形试样的晶间腐蚀敏感性进行了测试和对比。结果表明:热力学计算的平衡态Cr₂₃C₆碳化物析出温度范围为512~847 ℃,而通过时效试验验证的实际析出温度范围为720~940 ℃,表明二者之间存在约200 ℃的误差。当总变形量不超过20%时,等温变形非平衡态Cr₂₃C₆碳化物析出下限温度进一步降低至625 ℃,等温变形过程对晶界Cr₂₃C₆碳化物形核和长大过程均有加速作用。DL-EPR电化学方法结果表明等温变形后由于碳化物析出速度的加快,0Cr14Mn21NiN无磁不锈钢的晶间腐蚀敏感性显著增加。