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High-temperature alloys

Single-crystal performance boost

Nature Materials volume 15, pages 823–824 (2016)Cite this article

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Titanium aluminide alloys are lightweight and have attractive properties for high-temperature applications. A new growth method that enables single-crystal production now boosts their mechanical performance.

The usual poor room-temperature ductility of TiAl alloys is due to their phase composition: α2-Ti3Al and γ-TiAl, the major phases in these materials, do not contain a sufficient number of primary dislocation slip systems for large-scale plastic deformation3. This is further aggravated by considerable uptake of oxygen into the α2 phase during high-temperature exposure in air, which leads to the blocking of dislocation movement by oxygen interstitials, causing strain at fracture to drop from around 1.5% to less than 0.5% (ref. 4). Furthermore, a ductile–brittle transition temperature exists at around 650 °C (ref. 5), while the creep strength of the current polycrystalline TiAl alloys does not yet allow their use at temperatures above 800 °C. This limits their use in turbine engines, meaning they cannot replace Ni-based alloys in hotter sections of the engine. The authors of the current paper2 therefore aimed to achieve a significant improvement in the mechanical properties of these alloys at ambient and high temperatures, going beyond current application limits.

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Figure 1: Degradation of room-temperature strength (blue) and ductility (red) of a polycrystalline TiAl alloy (Ti–48Al–2Cr–2Nb) after exposure to air at different temperatures for 100 hours.
Figure 2: The single-crystal alloys reported by Chen et al.2 show only a slight reduction in mechanical performance, up to a temperature of approximately 900 °C (vertical dashed line).

References

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  2. Chen, G. et al. Nature Mater. 15, 876–881 (2016).

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  1. Michael Schütze is at DECHEMA-Forschungsinstitut, Frankfurt, Germany,

    Michael Schütze

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  1. Michael Schütze
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Correspondence to Michael Schütze.

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Schütze, M. Single-crystal performance boost. Nature Mater 15, 823–824 (2016). https://doi.org/10.1038/nmat4712

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