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

含少量Ti_3Al（α_2）的双相TiAl（γ）合金作为一类新型的高温材料引起了人们极大的兴趣。当通过锭冶金方法生产时，这种TiAl合金表现出层状显微组织。由于{111} _<gamma>//（0001）_<alpha2>，[110] _<gamma>// [1120] _的取向关系，片层组织中存在六种不同取向的TiAl变体<alpha2>。这导致除了α_2/γ层状界面之外，还出现三种不同类型的γ/γ层状界面。我们调查了成分变化的三种不同类型的γ/γ层状界面附近的二元和一些三元TiAl合金的透射电子显微镜配备了场发射枪，其中使用的电子探针小至0.5 nm。同时，我们研究了这些合金的机械性能，以了解是否发生 ...更多信息 γ/γ层状界面处的组成变化是否影响界面强度。没有证据表明成分变化检测在有序的双γ/γ界面的任何合金的调查。另一方面，在高能量的边界（120 Ω-旋转和赝孪晶γ/γ界面），我们观察到的成分变化，这与合金元素。Ti原子偏析到这两种类型的界面上观察到的二元，Mn和Nb掺杂的合金，而不仅是Ti原子，但也观察到合金元素偏析有Cr，Mo和Ta掺杂的合金。我们已经观察到，失败往往发生在整个片层边界的合金成分变化的边界时，拉伸试验与片层边界从加载轴倾斜，表明边界强化与合金元素的偏析。然而，垂直于片层边界的拉伸试验表明，失效平行于边界发生，没有拉伸伸长率。这表明，合金元素偏析的强化程度不够大，边界不会在垂直于边界的应力下裂开。少

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