Grain Refinement and Microstructure Formation by Inoculation

以往的研究主要集中在Ti-45Al-xB合金中的初生相β(Ti)和包晶相α(Ti)的非均匀形核。这些颗粒是为了细化β(钛)而非原位添加的，或者是在包晶α(钛)之前原位形成的。第三阶段的重点是Al含量较高(49~51at.%)、B含量适当(0.0aT~1.5at.)的合金中α(Ti)相的异质形核和细化。%)。在此成分范围内，α(Ti)相不再是包晶，而是初生相。与体心立方β(钛)不同，α(钛)具有六方晶格结构，这最终导致了不同的形核行为和生长动力学。TUHH小组将考虑α(钛)在铸造条件下的异质形核，从母材-复合材料中异地引入TiB_2孕育剂。他们将使用自由生长模型来分析晶粒细化。这些研究将通过Geesthacht的HZG小组进行的TiB_2形貌、TiB_2α(钛)界面和晶格取向关系的表征来完成。应采用扫描和透射式电子显微镜以及同步辐射高能x射线衍射。访问组将使用定向凝固实验来研究α(钛)的生长。将进行相场模拟，以深入了解组织形成的细节，并在形核和早期组织演变之间架起一座桥梁。作为最终目标，项目组寻求对成分范围内的Ti-44…的各种操作细化机制进行全面描述51Al-0…2B，基于热力学和结晶学数据以及对自由生长模型和相场模拟有效的一组独特的形核模型参数。

The previous funding periods focused on the investigation of grain refinement of primary β(Ti) and of peritectic α(Ti) in Ti-45Al-xB alloys due to heterogeneous nucleation on TiB2 particles. These particles were added ex-situ for β(Ti) refinement or formed in-situ just before peritectic α(Ti). This third period shall focus on heterogeneous nucleation and grain refinement of the α(Ti) phase in alloys with higher Al (49 to 51 at.%) and adequately chosen B contents (0.0 to 1.5 at. %). For this composition range, the α(Ti) phase is no longer peritectic, but primary. Different to bcc-β(Ti), α(Ti) crystallizes in a hexagonal lattice structure, which eventually leads to different nucleation behavior and growth kinetics. The TUHH group will consider the heterogeneous nucleation of α(Ti) under casting conditions, with TiB2 inoculants being introduced ex-situ from a master-composite. They will analyze the grain refinement using the free growth model. These studies will be accomplished by the characterization of TiB2 morphology, of TiB2α(Ti) interfaces and crystal lattice orientation relationships, being performed by the HZG group in Geesthacht. Scanning and transmission electron microscopy as well as high energy x-ray diffraction with synchrotron radiation shall be applied. The ACCESS group will investigate α(Ti) growth using directional solidification experiments. Phase field simulations will be performed to gain insight into the details of microstructure formation and to bridge the scale between nucleation and early microstructure evolution. As a final aim, the project team seeks for a comprehensive description of the various operating grain refinement mechanisms in the composition range Ti-44…51Al-0…2B, based on thermodynamic and crystallographic data and a unique set of nucleation model parameters valid for the free growth model and the phase field simulations.