Nb基超高温合金母合金锭的制备及定向凝固用坩埚的选择

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1、西北工业大学硕士学位论文Nb基超高温合金母合金锭的制备及定向凝固用坩埚的选择姓名：武兴君申请学位级别：硕士专业：材料加工工程指导教师：郭喜平20060301ABSTRACT㈧obium—basedalloyshavehi醵meltingpoints，relativelylowdensitiesandexcellentmechanicalpropertiesincludinghi酶temperature$瓣嶷g遗，loomtemgeratljrefracluretougkness，豁theyhave蟊燃thefocusofrecentstudies。Theyhavehighpote

2、mialforthefutureaerospaceapplications．Thecompositionsystems&niobiumbasedalloyshavebeendesignedinthispaper．TheingotswefeproducedbyVacuumself-consumablearcmelting．Theare—meltedmicrostrueturewasexan-dned键感ngallopticalmicroscope(OMXsea,ruingelectronmicroscope(SEM)筑静瓣檄vdth鼗energydispersiveX-rayspe

3、ctroscope(EDX)。到按cruciblesfordirectionalsolidificationwereselectedandexaminedL琦oughexperiments．TheresultsofSEMindicatedthatthemierostrueturewasuniformandconsistedoflargeamOuntSofeute确emidrOstructums．X,raydiffractionanalysisshowedthatthisare-meltedmicrostnietm罄删s醚ofniobiumsolidsolutieaft,rb瓣an

4、dniobiumsificidesfNbsSidNt廷Si)。NbsSi3基鑫s箍orderedstr燃a-e．TheanalysisofselectedareaelectrondiffractionpatternrevcaledthattherewerecertainorientationrelationshipsbetweenNbsSi3andNbss，Thatwas[010】／／[1351。Thesamplesofniobiumbasedalloyswereremeltedingraphitecrucibles,graphite．basedSiCcoated。：eraeib

5、les,graNite-based韪f冬c出atedcruciblesandBNertmibte&For蘸罄瓣phite掰端瓶theslh-fa麟of．tire劫融：has嚣镪i瘫燃of509rareactionlayer,瓣鼢．restdtant,prodnetion獬mainly翻carbidesoftitaniumandniobium，Thecross-likecarbidesarealSOfoundilinsidethealloybars．BecausethereactionordecompositionofSiCcoating，thereactionandproduct

6、ionWaSnearlythesa掰eas燃isthepuregraphitecrucibles。Becausethepreparationtechnologyof珞酶coatingWaSnotwelldevelolx／d,theY赫eoatinghadnotprevented瓣cruciblefromreactionwi爨themeltedalloy．ThereactionoftheNiobium-basedalloywasmuchmoreseverewhenre-meltedinaBNcruci；ble+andtherew．el'emanyeroseholesintheOUl

7、e：regionofthealloybars，Thethicknessofthereactionlayerisabout60pm，andthereweremanycavitiesfoundinsidethealloy．Thereactionproduct诞theBNca't

8、cibleismainly&nitrideofthetitaniumandniobium，’Keywords：niobiumbasedultrahigh·temperaturematerials，arc-me