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• Thermostable Al 20 Cu 2 Mn 3 intermetallic phase was precipitated by re-aging process. • The Al–Cu–Ce-Mn–Ni-Zr alloys exhibit outstanding tensile strength at 400 ℃. • The multi-scale intermetallic microstructure is the key to high-temperature strength. • The re-aging process can be a viable route for higher-temperature applications of aluminum alloys. Heat-resistant aluminum alloys are widely used in aerospace and automotive fields for manufacturing hot components due to their advantages in lightweight design and energy conservation. However, the high-temperature strength of existing cast aluminum alloys is always limited to about 100 MPa at 350 °C due to coarsening and transformation of strengthening phases. Here, we reveal that the yield strength and ultimate tensile strength of the T6 state Al–8.4Cu–2.3Ce–1.0Mn–0.5Ni–0.2Zr alloy at 400 ℃ increase by 34% and 44% after re-aging at 300 °C for 100 h, and its thermal strength exhibits distinguished advantage over traditional heat-resistant aluminum alloys. The enhanced elevated-temperature strength is attributed to the reprecipitation of the Ni-bearing T-Al 20 Cu 2 Mn 3 phase, whose number density increases over one time. The significant segregation of Ni, Ce, and Zr elements at the interfaces helps improve the thermal stability of the T phase. The thermostable T phase effectively strengthens the matrix by inhibiting dislocation motion. Meanwhile, a highly interconnected 3D intermetallic network along the grain boundaries can still remain after long-term re-aging at 300 °C, which is conducive to imposing a drag on the grain boundaries at high temperatures. This finding offers a viable route for enhancing the elevated-temperature strength of heat-resistant aluminum alloys, which could provide expanded opportunities for higher-temperature applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Intermetallic TiAl alloys attract much attention in advanced engineering fields due to their low density (3.9–4.2 g/cm3) and excellent high-temperature properties. After more than half a century of research and development, TiAl alloys have found applications in aerospace, automotive, and related industries. However, as a kind of semi-brittle materials, intermetallic TiAl alloys exhibit different mechanical behavior from metallic and ceramic materials. Thus, it is necessary to systematically understand their mechanical behavior to ensure further developments and safe engineering applications. In this paper, the principal mechanical behavior of TiAl alloys was reviewed comprehensively, including tension, creep, fatigue, and strengthening mechanisms. The mechanical performance and the corresponding deformation mechanisms are summarized and discussed in detail. The future directions of mechanical research on TiAl alloys are also overviewed to expedite their extensive utilization in engineering fields.

Assembling functional units into specific orientation organizations based on functional unit and organization (FUO) paradigm can maximize utilizing mechanical property anisotropy of lamellar-structured materials. However, the origin of their anisotropic deformation behaviors has not been clearly understood. Taking the fully lamellar γ-TiAl/α2-Ti3Al dual-phase single crystal as an example, we decouple the interface functional units governed anisotropic plastic deformation through in situtransmission electron microscopy tensile testing and multiscale microstructural characterizations. The orientation organization-dependent slip continuity across the γ/α2interface and interface strength play a determinant role in plastic anisotropy beyond intrinsic dislocation activities within the lamellae. Consequently, translamellar stress transfer or interface delamination prevails under the tension parallel or perpendicular to the lamella, elaborating the strong anisotropy in strength and ductility. These mechanistic insights hold general implications to understanding the anisotropic plastic deformation of lamellar-structured materials, benefiting the structural design of high-performance alloys.

• It is the first time that the high-temperature fatigue performance of PST TiAl single crystal has been studied;. • We found the PST TiAl single crystal can withstand more than 107 fatigue cycles under a stress amplitude of 270 MPa, which is significantly higher than traditional tial alloys;. • The high-temperature fatigue deformations were systematically investigated at atomic scale by transmission electron microscopy (TEM) observations and atomistic simulations. The improvement of fatigue resistance attributes to the plastic strain delocalization in uniform lamellae structure, and the plastic deformation is well-distributed and sufficient in each lamella. Polysynthetic twinned (PST) TiAl single crystal possesses great potentials for high-temperature applications due to its excellent combination of strength, ductility and creep resistance. However, a critical property for high-temperature application of such material involving high-temperature fatigue properties remains unknown. Here, the high-temperature high-cycle fatigue performance of PST TiAl single crystal has been studied. The result shows that PST TiAl single crystal can withstand more than 107 cyclic loadings at 975 °C under a stress amplitude of 270 MPa, which is significantly higher than traditional TiAl alloys. Experimental observations and atomistic simulations indicate that the improvement of fatigue resistance is attributed to the plastic strain delocalization in uniform lamellar structure, and the plastic deformation is well-distributed and sufficient in each lamella. Even in the α 2 lamella with difficult slippage, a large number of stacking fault structures can be observed. The 〈 c + a 〉 dislocations in α 2 tend to dissociate into a Frank partial with b = 1/6 <2 2 ¯ 0 3 ¯ >, forming a ribbon of I1 fault which ensures the continuity of deformation. [Display omitted] [ABSTRACT FROM AUTHOR]

TiAl 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 978 MPa due to the formation of extensive nanotwins during plastic deformation. At 900 °C yield strength remains high at 637 MPa, 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.