毕业设计位对TiNi合金马氏体相变的影响

毕业设计（论文）论文题目空位对TiNi合金马氏体相变的影响学生姓名学号所在院系专业班级机械设计制造及其自动化导师姓名职称完成日期摘要缺乏关于点缺陷的信息对于我们完全理解形状记忆合金是一个很大的障碍。我们利用第一原理密度泛函理论计算研究了在不同浓度的B2和R相中空位对TiNi合金马氏体相变的影响。我们发现，不需要聚合，空位可能在R相中引起剧烈的原子尺度局部晶格畸变，使其最邻近的环境像B2和R之间的中间结构。此外，B2相的能量低于R相，这说明，空位更倾向于使奥氏体稳定，而不是马氏体。这意味着空位会对B2→R转变产生一定的影响。空位之间的相互作用在两个阶段都有非常弱的吸引力，这说明空位可能引起浓度的短程变化，而不太可能引起沉淀物的形成。B2和R相的内聚能与马氏体相变温度的差异随着空位浓度的增加而降低，直到空位的含量超过临界水平，此时B2相自动变为R相，马氏体相变被完全抑制。由于R相中不同位置的空位具有不同的能量，所以空位对马氏体相变影响的程度可能会在材料的不同点位发生变化，因此，这也会造成材料的局部转变温度不同。关键词：马氏体相变；TiNi合金；VESTA；空位；第一计算原理EffectofVacancyonMartensiticTransformationofTiNiAlloyABSTRACTThelackofinformationaboutpointdefectsisabigobstacletoourfullunderstandingoftheprecursoryphenomenainshapememoryalloys.Usingthefirstprincipledensityfunctionaltheory,westudytheeffectofdifferentconcentrationsofB2andRphasevacanciesonmartensitictransformationofTiNialloy.WefindthatthevacancymaycausesevereatomicscalelocallatticedistortionintheRphase,makingitthemostadjacentenvironmentliketheintermediatestructurebetweenB2andR.Inaddition,thesolutionenergyoftheB2phaseislowerthanthatoftheRphase,indicatingthatthevoidstendtostabilizetheausteniteratherthanmartensite.Thismeansthatthevoidplaysananti-precursoreffectintheB2toRtransition.Theinteractionbetweenvacancieshasaveryweakattractioninbothstages,indicatingthatvacanciesmaycauseshort-rangechangesinconcentrationandarelesslikelytocausesedimentformation.ThedifferencebetweenthecohesiveenergyandthemartensitictransformationtemperatureofB2andRphasesdecreaseswiththeincreaseofvacancyconcentrationuntilthecontentofvacancyexceedsthecriticallevel,andthentheRphasebecomesB2phaseandthemartensitictransformationiscompletelyinhibited.SincethevacanciesatdifferentpositionsintheRphasehavedifferentsolutionenergies,theanti-precursoreffectofthevacancymaychangeatdifferentpointsofthematerial,andthereforethelocaltransitiontemperatureofthematerialwillbedifferent.Keywords:martensitictransformation；TiNialloy；VESTA；void；firstcalculationprinciple目录1绪论..................................................................................................................11.1引言...............................................................................................................11.2钛及其合金..................................................................................................11.2.1工业纯钛..................................................................................................11.2.2钛合金.......................................................................................................11.3关于马氏体相变..........................................................................................11.3.1马氏体相变的定义..................................................................................11.3.2马氏体相变的特点..................................................................................21.3.3马氏体相变的应用..................................................................................31.4关于空位.......................................................................................................41.5母相和马氏体相的结构..............................................................................41.6本论文研究的主要内容和意义.................................................................52模型和计算方法............................................................................................72.1引言...............................................................................................................72.2密度泛函理论..............................................................................................72.3VESTA.............................................................................................................72.4模型和计算..................................................................................................83数值结果......................................................................................................113.1空位在R-TiNi中的最优占位.................................................................113.2TiNi中空位之间的相互作用..................................................................133.3由于空位引起的原子尺度晶格畸变（ASLD）......................................143.4空位对B2→R相变能量的影响...............................................................163.5电荷密度.....................................................................................................183.6讨论.............................................................................................................204结论...............................................................................................................22参考文献.............................................................................................................23致谢......................................................................................................................24附录......................................................................................................................251绪论1.1引言TiNi合金是一种金属间化合物，它是工业领域一种十分重要的材料，它在电力、船舶、建筑、化工、航空航天等领域的应用非常广泛。TiNi合金具有很多的特殊性质，这之中最突出的是形状记忆效应及超弹性的钛合金和具有超低弹性模量的钛合金。这些钛合金在很多领域都得到了广泛的应用，潜移默化地改变着人们的生活。当温度或压力改变时，钛合