| Research Abstract |
The intermetallic compound AlィイD23ィエD2Ti is attractive as a potential high-temperature structural material because of its relatively high melting point, low density, and good oxidation resistance. However, it has the low-symmetry tetragonal DOィイD222ィエD2 structure and is very brittle at ambient temperature. One possible approach to ductilize ordered intermetallics with low-symmetry crystal structures is to change their structures to those of higher symmetry. The DOィイD222ィエD2 structure of AlィイD23ィエD2Ti can be changed to the related cubic LlィイD22ィエD2 structure with the addition of a third element, such as Zn, Ni, Cu, or Fe. Also, many studies on the Al-Ti-X (X=Ni, Fe, Cu, Mn, Cr, Ag and Pd etc.) systems have focused on the mechanical properties of the ternary LlィイD22ィエD2 trialuminide compounds. These (Al, X)ィイD23ィエD2Ti compounds will potentially have good oxidation resistance and some ductility because the LlィイD22ィエD2 structure has the requisite five independent slip systems required for
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homogeneous deformation. The ternary LlィイD22ィエD2 compounds, however, are still brittle in tension and/or bending, although they exhibit appreciable compressive ductility at ambient temperature. Recently, much work has been made on the microstrucure, especially second phases and porosity generally induced by a homogenization treatment, and the microstructure, especially second phases and porosity generally induced by a homogenization treatment, and the microstructure-mechanical property relationships of the ternary LlィイD22ィエD2 trialuminide compounds.
In the present study, we reported that Ti-9Mn-66Al and Ti-8Cr-67Al alloys with the LlィイD22ィエD2 structure does posses some intrinsic bend ductility at ambient temperature, and Ti-14Mn-61Al and Ti-14Cr-61Al alloys are more ductile in bending, with a plastic strain to 0.4% and 0.9% being recorded, respectively. In these higher manganese and chromium content alloys, no porosity was observed after homogenization. The formation of porosity was caused by Kirkendall mechanism with the second phases solutionized during homogenization treatment. Also recently, the respective bondings and coatings of LlィイD22ィエD2-type and LlィイD20ィエD2 (TiAl) alloys in the Al-Ti-Mn and Al-Ti-Cr systems were carried out to study functionally graded diffusion layers. Thus the microstructure and mechanical properties of the ternary LlィイD22ィエD2 compound are closely associated with the composition of LlィイD22ィエD2 formation and equilibrium second phases surrounding the LlィイD22ィエD2 phase. Less
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