钛合金因其高的比强度而越来越多地作为结构材料在工程中使用，这些钛合金常利用析出相变调节性能，因此深入理解析出相的形成机理是科学调控钛合金性能的前提。析出相形成机理的核心是关于各个取向界面的迁移性及影响迁移性的界面结构，然而目前对钛合金相界面迁移的原位研究报道比较缺乏，对钛合金界面结构的研究也还不完善，特别是缺乏析出相尖端界面结构的完整信息，导致难以确定不同取向界面上位错之间的相互关联，不利于理解界面位错伴随界面迁移过程中的运动。此外，前人对钛合金界面结构的研究基本都是从β中析出α，而少有考虑相变方向对界面结构的影响。本论文选用Ti-8Fe和Ti-2.6Mo合金，通过透射电镜对钛合金正逆相变的相变晶体学进行了系统的实验和理论研究，在此基础上利用原位热台观察研究了钛合金的相界面迁移。利用透射电子显微镜等手段表征了Ti-8Fe合金正转变（BCC→HCP）α析出相的形貌、晶体学和界面结构，重点研究了析出相尖端的界面结构，发现α析出相尖端界面含惯析面和侧面上位错环绕形成的位错网，该位错网由三组位错构成，运用位错消光法确定了这三组位错的柏氏矢量，并且定量表征了由两组位错构成的位错环的环面，运用O线模型和广义O单元方法圆满地解释了实验表征得到的结果。定量表征了Ti-2.6Mo合金逆转变（HCP→BCC）β析出相的形貌、位向关系以及惯析面、侧面和尖端的界面结构，采用最大位错间距作为O线判据计算的结果对惯析面结构进行了很好的解释，采用广义O单元方法计算的界面结构则与表征的尖端界面结构吻合得很好。通过与正转变析出相的界面结构进行对比分析，发现母相对析出相晶体学的影响主要在于惯析面位错的柏氏矢量，揭示了母相在析出相界面位错形成过程中可能扮演的重要角色。在表征清楚以上两个合金系统中的两相界面结构的基础上，运用原位加热样品台在透射电子显微镜下原位加热观察相界面的迁移，结果表明Ti-8Fe合金正转变两相组织原有界面不迁移，Ti-2.6Mo合金逆转变的刻面以台阶机制迁移，尖端可连续迁移，各个相界面的迁移具有强烈的各向异性。通过原位观察到的界面位错和台阶的行为，结合静态界面结构表征结果，提出了界面迁移过程中台阶和位错可能的运动模式。

Titanium alloys are widely used as structural materials in many fields due to their high strength to weight ratio. The superior property relies on the microstructures of the alloys which are often strengthened by precipitation. The precipitation process is essentially the interface migration and closely related to the interfacial structures. Consequently, a comprehensive understanding of the interphase boundaries is fundamental to control the microstructures and improve the properties. However, studies on the interfacial structures and interface migration of titanium alloys are still not enough, including the structure of the end face, the interfacial structure of α to β phase transformation and the interface migration. In this work, the interfacial structures of α precipitates in a Ti-8wt%Fe alloy and β precipitates in Ti-2.6Mo have been systematically investigated using transmission electron microscopy (TEM). Also, interface migration has been studied in a Ti-2.6wt%Mo alloy with in-situ TEM. Crystallography of α precipitates in a Ti-8wt%Fe alloy has been investigated in detail using TEM, especially the interfacial structure of end face. A dislocation network consisting of three sets of dislocation was observed on the curved end face. Burgers vectors of the dislocations were determined by contrast analysis, and the planes of the loops formed by the three sets of dislocations were quantitatively determined to be irrational planes. The crystallographic features including the orientation relationship (OR) between two phases, interfacial structures of the well-defined habit plane and curved end face of the precipitates have been well interpreted by O-line model and a generalized O-element approach. The crystallographic features of the β precipitates of a Ti-2.6wt%Mo alloy in HCP to BCC transformation have been studied systematically, including OR, the habit plane orientation, the interfacial structures of the habit plane and the curved end face of the tip. The Burgers vectors of the dislocations on the habit plane, side facet were determined by high resolution scanning transmission electron microscopy (HRSTEM). Two types of dislocations with different Burgers vectors were observed among the set of parallel periodic dislocations on the habit plane, which is different from the BCC to HCP transformation. A complex dislocation network was also observed on the curved end face of the tip of the β precipitate of this reverse phase transformation, and characterized quantitatively. These measured results were explained with crystallographic model very well and compared with the crystallography of BCC to HCP transformation. The comparison results implies that the structure of the matrix may influence the Burgers vectors of the dislocations in the habit plane of the precipitates.Based on the characterized structures of the interphase boundaries of α?β phase transformation，interface migration was investigated by in-situ heating the TEM sample of the Ti-8Fe and Ti-2.6Mo alloy on TEM. The preexisting α precipitates in the Ti-8Fe alloy were observed to be stable during heating, while the β precipitates in the Ti-2.6Mo alloy were observed to shrink. The interface of the β precipitates migrates via lateral motion of growth ledges, and normal motion of the interface was not found. The migration is strongly anisotropic, i.e., the end face of the tip of the precipitate migrates much faster than the habit plane which contains less dislocations. The evolution of the ledges and dislocations on the facets of the β precipitates was also analyzed based on the in-situ observations and theoretically calculated interfacial structures.