the abstract of the paper the team has published in Journal Nature:http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4677.htmlPolysynthetic twinned TiAl single crystals for high-temperature applicationsTiAl alloys are lightweight, show decent corrosion resistance and have good mechanical properties at elevated temperatures, making them appealing for high-temperature applications. However, polysynthetic twinned TiAl single crystals fabricated by crystal-seeding methods face substantial challenges, and their service temperatures cannot be raised further. Here we report that Ti–45Al–8Nb single crystals with controlled lamellar orientations can be fabricated by directional solidification without the use of complex seeding methods. Samples with 0° lamellar orientation exhibit an average room temperature tensile ductility of 6.9% and a yield strength of 708 MPa, with a failure strength of 978MPa due to the formation of extensive nanotwins during plastic deformation. At 900°C yield strength remains high at 637MPa, with 8.1% ductility and superior creep resistance. Thus, this TiAl single-crystal alloy could provide expanded opportunities for higher-temperature applications, such as in aeronautics and aerospace.At a glanceleftright![[IMG]](https://c2.staticflickr.com/8/7406/27754066141_28e391eb2c_o.jpg "Click this image to show the full-size version.") a, Bright-field TEM image of a tensile specimen showing the original α2/γ lamellar structure before the test. b, After the tensile deformation, the bright-field TEM image reveals the ultrafine twinning and lamellar structure, with the selected area electron diffraction pattern (inset). c, A high-resolution (HR) TEM image of the deformed specimen showing multiple-twinned structures containing three twin boundaries γA/γB, γB/γC and γC/γD.![[IMG]](https://c2.staticflickr.com/8/7326/27754064541_22d09d4d46_b.jpg "Click this image to show the full-size version.") a, Mechanical properties as a function of temperature. The well-aligned PST single crystal maintains a high yield strength of 637MPa at 900°C; a temperature much higher than the 650–750°C reported for polycrystalline alloys4 (see the pink-colour region in the figure). b,c, The true stress–strain curve and the work hardening rate obtained at ambient temperature (b) and 900°C (c). d, TEM microstructure of well-aligned PST single crystals after tension tested at 900°C. Twins and dislocations appear simultaneously after the elevated-temperature deformation.
![[IMG]](https://c2.staticflickr.com/8/7281/27728707282_06440629fc_o.jpg "Click this image to show the full-size version.")
a, Creep strain–lifetime curves. The red lines are for the Ti–45Al–8Nb PST single crystals and the blue lines for the 4822 alloys. The inset is the creep strain–lifetime curves of the 4822 commercial alloy under stresses of 150 and 210MPa. b, Comparison of the minimum creep rates of the single and polycrystalline materials.
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