简介:Themicro-characteristicsofthestreakymarksandthecorrespondingsubstratesurfaceofgalvannealed(GA)steelsheetshavebeeninvestigatedusingSEMandFIB.Thestreakymarkareaseemstohavemanycavities,similartocraters,whichscatterlightandmakethesurfaceappeardarkerwhencomparedwiththesurroundingnormalarea.Moreover,itisfoundthattheirregularityordifferenceinsteelgrainsizetendstoaffectthesurfacequalityoftheGAsteelsheets.Duringalloying,thediffusionspeedofZn-Feonthegrainboundaryisfasterthanthatatthecenterofthegrain,whichresultsintheselectiveformationofcrater-likemorphologyinthecoatingareawithlargersteelgrains.DuetothecleargrainboundaryofIFsteel,apparentstreakymarkswillbeformedonthecoatin,iftheIFsteelsurfaceconsistsofrainsofirreularsize.
简介:Geologicmarksrelatedtoextraterrestrialimpactevents,suchasimpactsplitgravels,impactbrecciatelayers,impactdikes,microirghizites,microtektites,especiallymeteoriticresidues,werediscoveredontheboundarybetweenSinian/CambrianatTianmenshanofWesternHunan,whichmaypossiblydemonstratethatanextraterrestrialimpacteventhaseveroccurredthereontheS/Cboundary.