定向凝固Sn_Ni包晶合金糊状区熔化与凝固行为.docx

Classified Index: TG111.4; 113.12U.D.C: 67.80.bf, 68.35.bdDissertation for the Doctoral Degree in EngineeringMELTING AND SOLIDIFICATION BEHAVIOURIN THE MUSHY ZONE OF DIRECTIONALLYSOLIDIFIED Sn-Ni PERITECTIC ALLOYCandidate： Peng pengSupervisor： Academician Fu HengzhiAssociated Supervisor： Prof. Guo JingjieAssistance Supervisor： Associate Prof. Li XinzhongAcademic Degree Applied for： Doctor of EngineeringSpeciality： Materials Processing EngineeringAffiliation： School of Materials Science andEngineeringDate of Defence： 2013.6Degree Conferring Institution： Harbin Institute of Technology摘 要- I -摘 要本文以初生相 Ni3Sn2和包晶相 Ni3Sn4均为具有小固溶度有序金属间化合物的 Sn-Ni 包晶合金(L+Ni3Sn2Ni3Sn4)为研究对象，采用 Bridgman 法定向凝固工艺研究其在高温度梯度下静态糊状区与动态糊状区内的熔化与凝固行为及其对凝固组织的影响规律。在定向凝固 Sn-36at.%Ni 包晶合金的静置热稳定处理过程中，在未熔固相区与完全液相区间，形成对应一定凝固区间的固液共存的静态糊状区。此静态糊状区可分为初生相静态糊状区与包晶相静态糊状区，前者与完全液相区之间界面为定向凝固初始固/液界面。随静置热稳定处理时间的延长，糊状区内液相体积分数逐渐减小，固相沿温度梯度方向排列；同时，初始固/液界面下移至低温位置且逐渐平直。而包晶反应温度 TP处的初生相静态糊状区/包晶相静态糊状区界面出现“平滑”“曲折”“平滑”的转变现象。这是因为温度梯度的存在会引起温度梯度区域熔化效应(TGZM：Temperature gradient zonemelting)，引起糊状区内不同位置发生熔化或凝固现象。基于质量守恒定理，计算了静置热稳定处理过程中 Sn-36at.%Ni 包晶合金初始固/液界面前沿完全液相区中的溶质浓度。与其他合金系的对比表明：Sn-Ni 包晶合金具有较大的凝固区间及初生相/包晶相与液相溶质浓度差，所以完全液相区的溶质浓度与合金初始浓度差异较大。相比将包晶两相设为完全无固溶度的金属间化合物，当考虑初生相与包晶相的固溶度时，完全液相区的溶质浓度与合金初始浓度差异较小，更符合实际情况。此外，静置热稳定处理过程中，在固/液界面前沿液相中发现 Ni 原子的贫乏区，由于溶质对流的影响，随着静置热稳定处理时间的增加，此贫乏区逐渐消失，固/液界面前沿液相溶质分布更加均匀。研究了不同静置热稳定处理时间对定向凝固 Sn-36at.%Ni 包晶合金后续定向凝固组织的影响。在常用的静置热稳定处理时间范围内，Sn-36at.%Ni 包晶合金，定向凝固初始固/液界面均为非平界面，定向凝固包晶合金中各相的凝固顺序及生长机制也未发生改变。生长速度为 v=1m/s 时，Ni/Sn 原子的贫化/富集程度越大，越容易长成枝晶形态，即生长过程的有序程度增大。而v=10m/s 时，Ni/Sn 原子的贫化/富集程度越大，越容易长成发达枝晶形态，即生长过程的无序程度增大。在定向凝固 Sn-36at.%Ni 包晶合金动态糊状区凝固组织中观察到了明显的哈尔滨工业大学工学博士学位论文- II -二次枝晶粗化现象，同时发现包晶反应明显抑制了粗化过程。为了解释此现象，提出了耦合包晶反应与 Gibbs-Thomson 效应的二次枝晶粗化模型，并进行了合理解释。利用二次枝晶间距(2)与枝晶比表面积(SV)表征了动态糊状区内的粗化过程，而且通过上述表征参数也可确定实际凝固过程中的包晶反应程度。通过模型计算结果与实验结果比较可知：比表面积 SV较之 2更适合作为表征参数。在定向凝固 Sn-36at.%Ni 包晶合金动态糊状区内也观察到由温度梯度引起的 TGZM 效应导致的二次枝晶臂上的熔化/凝固现象；而且发现当存在三次枝晶臂时，在两二次枝晶臂间液相上方二次臂上发现一“锯齿状”形貌。提出了描述三次枝晶臂存在时二次枝晶臂上的熔化/凝固模型，可很好的表征三次枝晶臂对二次枝晶臂迁移的影响。同时发现包晶反应越完全，这种“锯齿状”形貌越明显。针对定向凝固包晶合金动态糊状区内的“分离式包晶反应”现象，提出了耦合包晶反应、Gibbs-Thomson 效应及 TGZM 效应的分离式包晶反应动力学模型。基于溶质守恒提出了考虑固相反扩散与枝晶粗化并耦合 TGZM 效应的动态糊状区二次枝晶臂间微观偏析模型。合理描述了二次枝晶臂间的微观偏析。通过实验与模型计算结果的对比发现：在高温度梯度作用下，耦合TGZM 效应对二次枝晶臂间的微观偏析的计算有很大影响。根据模型计算结果，当仅考虑 Gibbs-Thomson 效应，而未耦合 TGZM 效应时，包晶反应抑制了粗化过程的进行，即促进了微观偏析。而当耦合 Gibbs-Thomson 效应与TGZM 效应后，二次枝晶臂间的微观偏析会得到抑制。在定向凝固 Sn-22at.%Ni 包晶合金动态糊状区内发生了领先相的转变，平衡凝固时作为领先相的 Ni3Sn2被包晶相 Ni3Sn4取代。提出了具有小固溶度的金属间化合物平界面凝固时溶质再分配模型合理解释了上述转变现象。随着凝固距离的增加，固液界面前沿液相的溶质浓度按多项式函数减小。这与关于固溶体或完全无固溶度的符合化学计量比的金属间化合物均不同。同时由于具有小固溶度的金属间化合物其成分不可能与合金初始浓度相同，固液界面前沿液相中将不存在稳态边界层。关键词：Sn-Ni 包晶合金；糊状区；熔化与凝固；定向凝固；TGZM 效应国内图书分类号：TG111.4; 113.12 学校代码：10213国际图书分类号：67.80.bf, 68.35.bd 密级：公开工学博士学位论文定向凝固 Sn-Ni 包晶合金糊状区熔化与凝固行为博 士 研 究 生：彭鹏导 师：傅恒志 院士副 导 师：郭景杰 教授协 助 指 导：李新中 副教授申 请 学 位：工学博士学 科：材料加工工程所 在 单 位：材料科学与工程学院答 辩 日 期：2013.6授予学位单位：哈尔滨工业大学Abstract- III -AbstractIn this study, Sn-Ni peritectic alloys exhibiting peritectic reactionL+Ni3Sn2Ni3Sn4in which the primary Ni3Sn2phase and peritectic Ni3Sn4phaseare intermetallic compounds with narrow solubility, have been chosen forinvestigation. The melting and solidification process in the stationary mushy zonesand moving mushy zones of Sn-Ni peritectic alloys are studied in steep temperaturegradient through Bridgman-type directional solidification apparatus.During the thermal stabilization of Sn-36at.%Ni peritectic alloys, a stationarymushy zone where the solid and liquid coexist is formed between the non-moltensolid zone and complete liquid zone. This stationary mushy zone can be dividedinto the primary stationary mushy zone and peritectic stationary mushy zone. Theinterface between the former stationary mushy zone and the complete liquid zone isthe initial solid/liquid interface of directional solidification. With the increase of thetime of thermal stabilization of stationary mushy zone, the volume fraction of liquidin the mushy zones gradually decreases, and the solid phases arrange parallel to thedirection of temperature gradient. Meanwhile, the initial solid/liquid interfacemoves downward to positions with lower temperatures and becomes planargradually. The primary phase/peritectic phase interface at the peritectic reactiontemperature TPevolves from “flat”“zigzag”“flat”. The reason is thattemperature gradient lead to the TGZM(temperature gradient zone melting)mechanism, thus melting/solidification occur at different positions in the mushyzone.The solute concentration in liquid ahead of the initial solid/liquid interface ofSn-36at.%Ni peritectic alloys is calculated based on the law of conservation ofsolute. Comparison with other alloy systems shows that the difference in soluteconcentration between the complete liquid zone and the concentration of alloy isrelatively larger in Sn-Ni peritectic alloy. This can be attributed to relatively largerfreezing range and difference in solute concentration between solid phases andliquid of Sn-Ni peritectic alloy. In addition, as compared to intermetalliccompounds with nil solubility, when the solubility of both primary and peritecticphases are taken into consideration, the calculation is more close to theexperimental results. Moreover, during the thermal stabilization of Sn-36at.%Niperitectic alloys, a solute Ni depleted zone is formed in liquid ahead of thesolid/liquid interface. With the increase of thermal stabilization time, this depletedzone disappears due to solutal convection, and distribution of solute concentrationAbstract- V -interpreted through this model. Besides, the melting/solidification process inducedby the TGZM effect is dominant in presence of a steep temperature gradient. In thiscase, the retard of coarsening process by peritectic reaction is restricted. The rangeof the reaction constant f characterizing the completeness of peritectic reaction isnot constant but ranges from 0.3 to 0.7 with increasing growth rates. The rangedetermined in the present work is larger than that determined without considerationof the TGZM effect while the scopes of them are close to each other.The transfer of the leading phase is found in the moving mushy zones of Sn-22at.%Ni peritectic alloy. The Ni3Sn2 phase which is the leading phase dudringequilibrium solidification is replaced by peritectic Ni3Sn4 phase. A model isproposed to describe the solute redistribution during planar solidification ofintermetallic phase with narrow solubility. Transfer of leading phase discussedabove can be explained reasonably well with this model. It is found that the soluteconcentration in liquid ahead of the solid/liquid interface decreases polynominallywith the increase of solidification distance, which is distinct from solid solutionphases and intermetallic phases with nil solubility. Besides, as the initialconcentration of alloy can not be the same as concentration of intermetallic phasewith narrow solubility, steady-state boundary layer will not exist in the liquid aheadof the solid/liquid interface.Keywords: Sn-Ni peritectic alloys; Mushy zones; Melting and Solidification;Directional Solidification; TGZM effect目 录- V -目 录摘 要.IAbstract .III第 1 章 绪 论.11.1 课题目的和意义. 11.2 糊状区的熔化与凝固 . 31.2.1 糊状区的形成与分类 . 31.2.2 糊状区熔化与凝固对糊状区组织的影响 . 51.3 温度梯度作用下糊状区的熔化与凝固. 91.3.1 静态糊状区的熔化与凝固. 91.3.2 动态糊状区的熔化与凝固. 151.3.3 不同糊状区交互作用下的熔化与凝固 . 181.4 化合物相的熔化与凝固.201.4.1 化合物相的凝固特性 . 201.4.2 糊状区中化合物相的熔化与凝固 . 211.5 本文主要研究内容 .22第 2 章 实验材料与方法 .252.1 实验材料及其制备 .252.2 Sn-Ni 包晶合金糊状区的制备 .252.2.1 感应加热定向凝固装置 . 252.2.2 定向凝固初始固/液界面准备实验 . 262.2.3 定向凝固实验 . 272.2.4 定向凝固系统温度梯度的测量 . 272.3 试样的处理与分析 .28第 3 章 定向凝固启动前 Sn-Ni 包晶合金静态糊状区内熔化与凝固行为 .293.1 引言 .293.2 静态糊状区的形成及其演化 .303.2.1 静态糊状区形成机制 . 303.2.2 静态糊状区组织演化 . 313.2.3 静态糊状区内熔化与凝固机制 . 343.2.4 不同静态糊状区交界处熔化与凝固机制 . 34目 录- VII -4.7 本章小结.108第 5 章 耦合 TGZM 效应与 G-T 效应的分离式包晶反应机制 .1105.1 引言 .1105.2 耦合 TGZM 效应与 G-T 效应的分离式包晶反应模型. 1115.2.1 Stage I . 1135.2.2 Stage II . 1165.2.3 Stage III . 1185.2.4 Stage IV . 1195.3 分离式包晶反应对微观偏析的影响 .1225.3.1 二次枝晶臂间的微观偏析. 1235.3.2 耦合分离式包晶反应的微观偏析模型 . 1245.4 本章小结.131结 论 .133参考文献.135攻读博士学位期间发表的论文及其他成果.152哈尔滨工业大学学位论文原创性声明和使用权限.154致 谢.155个人简历.156哈尔滨工业大学工学博士学位论文- VI -3.3 固/液界面前沿液相成分 .383.3.1 静态糊状区成分分析 . 383.3.2 固液界面前沿液相成分分析 . 383.3.3 固/液界面前沿液相溶质浓度模型 . 413.3.4 固/液界面前沿液相成分的影响因素 . 473.4 静置热稳定处理对后续定向凝固组织的影响.483.4.1 凝固组织分析方法 . 503.4.2 热稳定处理对后续定向凝固胞晶组织的影响 . 513.4.3 热稳定处理对后续定向凝固枝晶组织的影响 . 563.5 本章小结.60第 4 章 定向凝固 Sn-Ni 包晶合金动态糊状区内熔化与凝固行为 .624.1 引言 .624.2 定向凝固 Sn-Ni 包晶合金动态糊状区凝固界面形貌 .624.2.1 定向凝固 Sn-Ni 包晶合金界面形貌演化 . 624.2.2 定向凝固 Sn-Ni 包晶合金界面形貌演化临界速度 . 654.3 动态糊状区的枝晶粗化.654.3.1 粗化的原理及表征 . 654.3.2 枝晶粗化模型的选择 . 694.4 动态糊状区枝晶粗化模型 .714.4.1 Stage I . 764.4.2 Stage II . 774.4.3 Stage III . 794.4.4 粗化程度的测量与计算 . 804.4.5 计算与实验结果对比 . 834.5 动态糊状区发达枝晶组织中的熔化/凝固行为 .884.5.1 动态糊状区发达枝晶组织中的熔化/凝固现象 . 884.5.2 动态糊状区发达枝晶组织中的熔化/凝固模型 . 904.5.3 包晶反应对熔化/凝固的影响 . 944.6 动态糊状区内的相转变.974.6.1 动态糊状区内的相转变现象 . 974.6.2 动态糊状区内相转变模型. 994.6.3 共晶合金系 . 1014.6.4 包晶合金系 . 1024.6.5 相固溶度对固液界面前沿溶质再分配的影响 . 1044.6.6 稳态浓度分布的条件 . 107哈尔滨工业大学工学博士学位论文- IV -in liquid ahead of the solid/liquid interface is more and more uniform.The influence of thermal stabilization on following directional solidificationmicrostructure is investigated in Sn-36at.%Ni peritectic alloys. The results showthat: for Sn-36at.%Ni peritectic alloys, the initial solid/liquid interface ofdirectional solidification is not planar in the range of common thermal stabilizationtime. Besides, the solidification sequence and growth mechanism of the phases doesnot change. At the growth rate of 1m/s, if depletion/enrichment of Ni/Sn atoms aremore obvious, dendrite morphology is more developed, and the microstructure ismore ordered. At the growth rate of 10m/s, if depletion/enrichment of Ni/Sn atomsare more obvious, dendrite morphology is more developed, and the microstructureis less ordered.Obvious coarsening phenomenon can be observed in the moving mushy zonesof directionally solidified Sn-36at.%Ni peritectic alloy; meanwhile, the restrictionon coarsening process by peritectic reaction has also been found. A coarseningmodel which takes into account of both peritectic reaction and coarsening process isproposed. And this model can well describe the coarsening process in peritecticalloy. The secondary dendrite arm spacing 2and the specific surface of dendritesSVare used to characterize the coupling effects of above factors. Comparisonbetween calculation and experimental results shows that SVis more applicable tocharacterize the melting/solidification process as compared with 2.Simultaneously, the melting/solidification process caused by the TGZMmechanism which is induced by temperature gradient can also be observed. Besides,in the presence of the tertiary dendrite arms, a “sawtooth” like morphology can befound on the secondary dendrites. This morphology is caused by different soluteconcentration on secondary dendrites with and without tertiary dendrites. A modelis proposed to describe this morphology, and can well characterize this “sawtooth”morphology. This morphology is more obvious at higher growth rate and morecomplete peritectic reaction.The “divorced” peritectic reaction can be observed in the mushy zone