A high-temperature nanostructured Cu-Ta-Li alloy with complexion-stabilized precipitates.

We present a bulk nanocrystalline copper alloy that can operate at near-melting temperatures with minimal coarsening and creep deformation. The thermal stability of the Cu-3Ta-0.5Li atomic % (at %) alloy is attributed to coherent, ordered L12 Cu3Li precipitates surrounded by a tantalum-rich atomic bilayer phase boundary complexion. Adding 0.5 at % lithium to the immiscible Cu-Ta system changes the morphology of the nanoscale precipitates from spherical to cuboidal while simultaneously tailoring the phase boundary. The resultant complexion-stabilized nanoscale precipitates provide excellent thermal stability, strength, and creep resistance. The underlying alloy design principles may guide the development of next-generation copper alloys for high-temperature applications such as heat exchangers. Editor's summary: In theory, nanocrystalline alloys should be able to retain considerable strength even at high temperatures, but this has rarely been demonstrated in practice. Hornbuckle et al. started with a binary alloy of copper (Cu) and tantalum (Ta), even though the two are immiscible, to which they added lithium (Li). This mixture resulted in precipitates of nanoscale clusters of Cu3Li coated with Ta. This core-shell structure neither dissolves nor coarsens at temperatures of up to 800°C while also causing the yielding strength to be in excess of 1 gigapascal. —Marc S. Lavine [ABSTRACT FROM AUTHOR]