鈦的力學性質及氫脆現(xiàn)象的分子動力學研究.pdf

1、復旦大學碩士學位論文鈦的力學性質及氫脆現(xiàn)象的分子動力學研究姓名：白顯明申請學位級別：碩士專業(yè)：物理電子學與光電子學指導教師：陸明張強基2000.5.1；【!上擎Ⅲ士掌位論文鈦的力掌性質及氨脆象的#子動力學H究TheMechanicalPropertiesofTitaniumandThePhenomenaofHydrogenEmbrittlementinTitanium：AMolecularDynamicsStudyAbstractApp

2、lyingMolecularDynamics(MD)tothestudyofthemechanicalpropertiesoftitaniumandthephenomenaofhydrogenembrittlementintitanium，followingworkshavebeenperformed：Thetemperature—dependentEmbedded—atomMethod(EAM)functionsoftitaniuma

3、redeterminedempiricallybyfittingtothelatticeconstants，elasticconstan|sandsublimationenergiesatvarioustemperaturesUnfortunatelytheseEAMfunctionsarelocallyanalyticalattheequilibriumsites，andtheyarenotappropriatetodescribet

4、hesituationswhentheatomsarefarawayfromtheirequilibriumsitesorthescalesoflatticeconstantschangelargelyAlternativelyamoreappropriateEAMpotentialfunctionisdeterminedbyfittingtotheROSEuniversalequationTheequationisafunctiono

5、fthelatticeconstant，sothedrawbackofthefirstmethodiseliminatedTheEAMfunctionderivedfromitisusedinthelatterMDstudyandtheresultsarefairlygoodTheatomiclevelmechanicalpropertiesofTitaniumunderuniaxialstressarestudiedwiththePa

6、rrinello—RahmanMDformalismTheresultsdemonstratethatwhentheexternalpressureislowerthanthecriticalpressure，thereisalinearrelationshipbetweenthepressureandtheelongationWhenthetemperatureisat300KthecalculatedYoung’smodulusis

7、29x10”Paabouttwicetimes∞theexperimentaldataItisreasonablebecausetherearenodefectsinourmodelWhenthepressureishigherthanthecriticalpressure，thelinearrelationshipdisappearsSimilarinvestigationsareperformedwhenthetemperature

8、isat500Kand700KTheresultsshowthattheYoung’smodulus，thecriticalpressureandthefracturepressuredecreaseslightlywhenthetemperatureincreasesTheseresultsdemonstratethattitaniumiseasiertobeelongatedandfracturewhenthetemperature

9、ishigherThehydrogenEmbritfiementintitaniumisalsostudiedwithMDTheEAMpotentialfunctionofhydrogenisdeterminedbyfittingtothehydrogenmigrationenergyandtheheatofsolutionintitaniumOuratomiclevelcalculationdemonstratesthatthehyd

10、rogentitaniumsystemiseasiertofracturethantitanium，whichiscalledhydrogenembrittlementOurinvestigationshowsthatthelargescalediffusionofhydrogenatomsintitaniuminducesthe”hydrogenenhancedlocalplasticity(HELP)”mechanismThisme