简介:采用回流焊接技术制备Au80Sn20/Cu焊点,研究其显微组织和剪切强度随回流焊接工艺参数之间的演变规律。结果表明:在焊接温度为310℃时,焊点界面处形成的(Au,Cu)5Sn金属间化合物(IMC)层随回流次数增加而增厚;IMC形貌由层状转变为扇贝状,最后成长为胞状;焊点剪切强度随回流次数增加而下降,回流1次后剪切强度为82.94MPa,回流20次后下降至54.33MPa;且回流焊接次数对焊点断口形貌和断裂方式造成影响:1次回流后在Cu/IMC界面发生韧性断裂;而3次和5次回流后断裂面分别出现在焊料中和IMC中,为韧性脆性混合断裂;回流次数超过10次后焊点发生脆性断裂。
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简介:TheelectronicpropertiesandtopologicalphasesofThXY(X=Pb,Au,Pt,PdandY=Sb,Bi,Sn)compoundsinthepresenceofspin–orbitcoupling,usingdensityfunctionaltheoryareinvestigated.TheThPtSncompoundisstableintheferromagneticphaseandtheotherThXYcompoundsarestableinnonmagneticphases.Bandstructuresofthesecompoundsintopologicalphases(insulatorormetal)andnormalphaseswithingeneralizedgradientapproximation(GGA)andEngel–Voskogeneralizedgradientapproximation(GGAEV)arecompared.TheThPtSn,ThPtBi,ThPtSb,ThPdBi,andThAuBicompoundshavetopologicalphasesandtheotherThXYcompoundshavenormalphases.Bandinversionstrengthsandtopologicalphasesofthesecompoundsatdifferentpressurearestudied.Itisseenthatthebandinversionstrengthsofthesecompoundsaresensitivetopressureandforeachcompoundasecond-orderpolynomialfittedonthebandinversionstrengths–pressurecurves.
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简介:Strongearthquakeactivityalovertheworldandstrong┐moderateearthquakeactivitywithinandnearChina(June~August,1995)PEI-SHANCHEN(陈培...
简介:Wehaveshownthat,incontrasttotheresultsintheliterature,theBraggpeakintensityofNi80Fe20/Cusuperlatticesisenhancedattheincidentx-rayenergyslightlyhigherthantheabsorptionedgeoftheheavierelement(Cu).TheatomicdensityatNi80Fe20/Cuinterfacewasanalysedbythediffractionanomalousfinestructuretechnologywiththeincidentangleofx-rayfixedatthefirstBraggpeak.OurresultsdemonstratetheepitaxygrowthofNi80Fe20/Cusuperlattices.Uponannealing,theepitaxityofNi80Fe20/Cumultilayersbecomespoorbutthelocalcrystallinityineachlayerisimproved.
简介:摘要“80/20教育法则”提供给我们一种独特的思考角度,教给我们一种分析问题的方法,给予我们许多的启示。本文从教材内容、教学结构、时间分配、整体与个别的矛盾和选题与作业评改的角度来阐述了80/20教育法则与地理综合复习课的整合。