Clarification of processes for ordering and precipitation of long-period superstructures in Al-rich TiAl rapidly solidified ribbons

在γ-TiAl的富al TiAl区形成了以L1_0结构为基础的长周期上层结构，有望成为高温耐热材料。富al TiAl合金的力学性能取决于这些上层组织的周期性结构、形貌和分布。在本研究中，利用含有低有序度上层结构的快速凝固带，阐明了富（Al, Ga） （Al, Ga） Ti区域的有序和析出过程。首先，通过详细的TEM观察发现，在富Al TiAl区形成的这些上层结构的稳定性很大程度上取决于退火温度和Al浓度。利润退火改变了稳定上层结构的结构和周期性。例如，通过h-Al_2Ti，上层结构由Al_5Ti_3变为r-Al_2Ti。根据晶体对称和上层结构的晶格失配来理解相变过程。第二年，研究的组成区域从Ti-Al二元扩展到Ti-Al- ga三元区域，以澄清有序过程和过渡上层结构。在Ti-Ga二元体系中，存在相对于L1_0矩阵具有5倍周期的ga_3ti_2型超结构，因此讨论了3 ~ 5倍周期的三种不同超结构之间的相稳定性。在富（Al, Ga） （Al, Ga） Ti区，L1_0基体相存在连续的固溶区，该区域根据退火温度和成分的不同出现了不同周期的超结构。随着Al浓度的降低或退火温度的降低，稳定相由2:1结构转变为3:2结构，经过5:3结构。这种过渡过程可以用浓度波的连续变化来解释。上述结果可以解析与γ-TiAl合金力学性能密切相关的上层组织的相稳定性和过渡过程。少

Some long-period superstructures based on the L1_0 structure are formed in the Al-rich TiAl region of γ-TiAl expected as high-temperature heat-resistance materials. Mechanical properties of the Al-rich TiAl alloys are controlled depending on periodic-structure, morphology and distribution of these superstructures. In this study, processes of ordering and precipitation were clarified in the (Al, Ga)-rich (Al, Ga) Ti region using rapidly solidified ribbons containing the superstructures with a low degree of order.Firstly, it was found by the detailed TEM observation that stability of these superstructures formed in the Al-rich TiAl region depends strongly on annealing temperature and Al concentration. Profit annealing changes the structure and periodicity of stable superstuctures. The stable superstructure was, for example, changed from Al_5Ti_3 to r-Al_2Ti through h-Al_2Ti. The transformation process was understood on the basis of crystal symmetry and lattice misfit of superstructures.T … More he next year, an investigated compositional area was expanded from the Ti-Al binary to the Ti-Al-Ga ternary region in order to clarify the ordering process and transitional superstructures. In the Ti-Ga binary system, the Ga_3Ti_2-type superstructure with 5-fold periodicity with respect to the L1_0 matrix exists, thus the phase stability was discussed among three superstructures with different periodic structures from 3 to 5 fold-periodicity. In the (Al, Ga)-rich (Al, Ga) Ti region, continuous solid-solution area of the L1_0 matrix phase exists and some superstructures with different periodicities appeared depending on annealing temperature and composition in this region. The stable phase changes from the 2 : 1 to 3 : 2 structure through the 5 : 3 structure with a decrease in Al concentration or annealing temperature. This transitional process was explained by an continuous change in {310) concentration waves.The above results can resolve phase stability and transitional process of the superstructures closely related to the mechanical properties of γ-TiAl alloys. Less