WCCo复合粉的原位合成与块体硬质合金的烧结

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1、北京工业大学博士学位论文WC-Co复合粉的原位合成与块体硬质合金的烧结姓名：刘文彬申请学位级别：博士专业：材料科学与工程指导教师：张久兴;宋晓艳20090301北京工业大学工学博士学位论文体材料。全面研究了SPS各工艺参数对烧结硬质合金块体显微组织和性能的影响。实验结果表明，超细复合粉的致密化开始于8040C，于11750C固相致密化结束：烧结温度、烧结压力和保温时间明显影响WC平均晶粒尺寸及尺寸分布进而影响力学性能。在优化工艺参数一烧结温度13250C、烧结压力50MPa、保温6．8min的条件下，获得W

2、C．6Co硬质合金块体材料的优良综合性能：硬度92．6HRA、断裂韧性12MPa·m¨2、横向断裂强度为2180MPa。探讨了复合粉中添加晶粒生长抑制剂对烧结块体WC晶粒尺寸和硬度、韧性的影响，并讨论了硬质合金块体材料的断裂机制。关键词WC．Co复合粉：原位反应合成：反应热力学；放电等离子烧结：力学性能ABSTRACTABSTRACTComparedtomicro·-grainedalloy,ultrafine·-grainedandnanocrystallinecementedcarbideshavemu

3、chhigherhardness，wearresistant，fracturetoughnessandtransverserupturestrength．Therefore，theresearchontheultrafine—grainedandnanocrystallineWC·Cocementedcarbidesbecomesanimportantdevelopingdirectioninthehardmetalindustry．ThesynthesisofWC—Copowderanditssinter

4、ingaretwokeystepsinpreparingtheultrafinestructuredcememedcarbides．Firstly,takingadvantageofsparkplasmasintering(SPS)technique，weinvestigatedtherapidrouteforsynthesisofWC-6wt．％Cocompositepowderbyinsitureductionandcarbonizationreactionsandimmediateconsolidat

5、ingthecompositepowderintothebulkinSPSsystem，usinglow—costtungstenoxide，cobaltoxideandcarbonblackasrawmaterials．Thewholeprocesswimthedurationlessthan30mincouldbedividedintofourstages，i．e．，theheatingofthepowdermixture，insitureductionandcarbonizationreactions

6、，sinteringdensificationandisothermalholding。Theeffectsofmillingtimeontheparticlesizeandsizedistribution，andtheeffectsoftheamountofcarbonadditioninthemixturepowders，thereactiontemperature，thesinteringtemperature，theholdingtimeandthesinteringpressureonthepha

7、sesandpropertiesoftheas-sinteredbulk，wereanalyzedsystematically．Thecementedcarbidesbulkswithhighdensityandgoodcombinedmechanicalproperties、Ⅳereobtained．ThemechanismoftherapidinsitupreparationofcementedcarbidesbulksintheSPSsystemWasproposedforthefrsttime．Ac

8、cordingtOthephenomenonofmeltingorboilingatthesinteringneckandthethermodynamicsofreactions，thereasonsoftheincreasedrateinthenon-equilibriumreactionsandthedifferencesofthereactionamountandthetypeandamountofther