共格畸变能作用下二元合金沉淀过程的计算机模拟

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1、西北工业大学硕士学位论文摘要本文采用微观相场模型，基于微观弹性力学理论和离散格点形式的微观扩散方群，在州内首先编制了包含共格畸变能的二元模型合余沉淀过程原子层面的计算机模拟程序，可用于研究二元置换型沉淀合金的共性问题，无需预先设定新相结构和相变路径，可自动描述可能的非平衡相、原子簇聚等，包容沉淀的全过程和全部成分范围，可获得沉淀组织的时间相关信息。共格畸变能可延缓低浓度合金和靠近低浓度合金一侧的中间浓度合金的沉淀过程，共格畸变能越大，浓度分布的起伏越小，达到平衡值后浓度分布曲线的凸起宽度越窄。靠近高浓度合金一侧的中间浓度

2、合金，随着共格畸变能的增大，沉淀机制由失稳分解和非经典形核长大的混合机制逐渐向非经典形核长大机制转变。共格畸变能在一定程度上阻碍了失稳分解，使其沉淀机制逐渐出典型的失稳分解机制转向失稳分解和非经典形核长大的混合机制。随畸变能的增大，沉淀相分布的耿向性越束越明显，由弥散分布的球状颗粒或“海绵状”结构，逐步趋于沿弹性“软”方向分布，形成类方格阵、纵横层状结构等。关键词：共格畸变能，沉淀机制，沉淀组织，模型合金，微观扩散方程IIAbstractWiththemicroscopicphase-fieldmodel，theatom

3、ic—scalecomputersimulationprogramsofthebinarymodelalloysincludingcoherentstrainenergyduringtheprecipitationwerefirstlyworkedoutbasedonthemicroscopicelasticitytheoryandmicroscopicdiffusionequation．Itcanbeappliedtothewholeprecipitationprocessandcompositionrange．Any

4、priorassumptionsonthenewphasestructureortransformationpathwasunnecessary,thepossiblenonequilibriumphasesandatomicclusteringcouldbedescribedautomatically，therelevantinformationoftimeoftheprecipitationstructureswereobtained．TheprecipitationCOursesofthelowcompositio

5、nalloysandthemedialdensityalloysnearthelowdensityalloyscouldbedelayedbythecoherentstrainenergy．Theheavierthecoherentstrainwas，thesmallerthefluctuationsofthecompositionprofileswere，andthenarrowertheprotrudingwidthofthecompositionprofilecurveswcrc．Withtheincreaseof

6、coherentstrainenergy,theprecipitationmechanismofmedialcompositionalloysileal"thehighdensityalloyswerebecomingfromthemixtureprocesseswhichpossedthecharacteristicsofbothnon—classicalnucleationgrowthandspinodaldecompositionmechanismstOtheprocesseswhichpossedonlythec

7、haracteristicsofnon-classicalnucleationgrowth．Thecoherentstrainenergyputoffspinodaldecompositiontoacertainextentandmadeitsprecipitationmechanismchangefromtypicalspinodaldecompositionmechanismtothemixtureprocesseswhichpossedthecharacteristicsofbothnon—classicalnuc

8、leationgrowthandspinodaldecompositionmechanisms．Withtheelasticstrainenergyincreased，thearrangementorientationincreased，fromspherical—shapedprecipitatesorfloccu