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Compositional inhomogenuity and mechanical properties of gamma/gamma interfaces in two-phase TiAl alloys

两相 TiAl 合金中 γ/γ 界面的成分不均匀性和力学性能

基本信息

批准号：
07650818
负责人：
INUI Haruyuki
金额：
$ 1.6万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Two-phase TiAl (gamma) alloys containing a small fraction of Ti_3Al (alpha_2) have attracted a great deal of interest as a new class of high-temperature materials. Such TiAl alloys exhibit a lamellar microstructure when produced by ingot metallurgy methods. There are six types of differently oriented TiAl variants in the lamellar structure because of the orientation relationship of {111} _<gamma>// (0001) _<alpha2>, [110] _<gamma>// [1120] _<alpha2>. This leads to the occurrence of three different types of gamma/gamma lamellar interfaces, in addition to alpha_2/gamma lamellar interfaces. We investigated compositional variation in the close vicinity of three different types of gamma/gamma lamellar interfaces for binary and some ternary TiAl alloys with a transmission electron microscope equiped with a field-emission gun where an electron prove of as small as 0.5 nm is used. At the same time, we investigated mechanical properties of these alloys in order to see whether the occurrence of … More compositional variation at gamma/gamma lamellar interfaces affects the interfacial strength or not. No evidence for compositional variation is detected at ordered twin gamma/gamma interfaces for any of the alloys investigated. On the other hand, at high-energy boundaries (120ﾟ -rotational and pseudotwin gamma/gamma interfaces), we observed compositional variation which varies with alloying elements. Segregation of Ti atoms onto these two-types of interfaces is observed for binary, Mn-and Nb-doped alloys whereas not only Ti atoms but also alloying element are observed to segregate there for Cr-, Mo- and Ta-doped alloys. We have observed that failure tends to occur across lamellar boundaries for alloys with compositional variation at the boundaries when tensile tests are made with the lamellar boundaries inclined from the loading axis, indicating the boundaries are strengthened with segregation of alloying elements. Tensile testing made perpendicular to the lamellar boundaries, however, reveals that failure occurs parallel to the boundaries with no tensile elongation. This indicates that the extent of strengthening with segregation of alloying elements is not large enough for the boundaries not to be cleaved against stresses normal to the boundaries. Less

含有少量Ti_3Al（α_2）的两相TiAl（γ）合金作为一类新型高温材料引起了人们的极大兴趣。当通过铸锭冶金方法生产时，这种TiAl合金表现出层状微观结构。由于{111} _<gamma>// (0001) _<alpha2>、[110] _<gamma>// [1120] _<alpha2>的取向关系，层状结构中有六种不同取向的TiAl变体。除了 alpha_2/gamma 层状界面之外，这导致出现三种不同类型的 gamma/gamma 层状界面。我们使用配备场发射枪的透射电子显微镜研究了二元和一些三元 TiAl 合金的三种不同类型的 γ/γ 层状界面附近的成分变化，其中使用的电子孔径小至 0.5 nm。同时，我们研究了这些合金的机械性能，以了解伽马/伽马层状界面处成分变化的发生是否会影响界面强度。对于所研究的任何合金，在有序孪生伽马/伽马界面处均未检测到成分变化的证据。另一方面，在高能边界（120°-旋转和假孪生伽马/伽马界面），我们观察到随合金元素变化的成分变化。对于二元、Mn 和 Nb 掺杂合金，观察到 Ti 原子在这两种类型的界面上偏析，而对于 Cr、Mo 和 Ta 掺杂合金，不仅观察到 Ti 原子而且合金元素也偏析在那里。我们观察到，当在从加载轴倾斜的层状边界进行拉伸试验时，对于边界处成分变化的合金，往往会发生跨层状边界的失效，这表明边界随着合金元素的偏析而得到强化。然而，垂直于层状边界进行的拉伸测试表明，失效发生在平行于边界且没有拉伸伸长的情况下。这表明合金元素偏析强化的程度不足以使边界在垂直于边界的应力下不被劈裂。较少的