Design of Stable Nanocrystalline Alloys

TLDR

Nanostructured metals are inherently unstable, with rapid grain growth at low temperatures, but alloying can improve stability in only a few empirically discovered systems. A nanostructure stability map based on a thermodynamic model is applied to design stable nanostructured tungsten alloys. Using this model, the authors designed stable nanostructured tungsten alloys, identifying W‑Ti as a candidate that shows markedly improved high‑temperature stability and a heterogeneous chemical distribution predicted by the framework but not expected from bulk thermodynamics.

Abstract

Nanostructured metals are generally unstable; their grains grow rapidly even at low temperatures, rendering them difficult to process and often unsuitable for usage. Alloying has been found to improve stability, but only in a few empirically discovered systems. We have developed a theoretical framework with which stable nanostructured alloys can be designed. A nanostructure stability map based on a thermodynamic model is applied to design stable nanostructured tungsten alloys. We identify a candidate alloy, W-Ti, and demonstrate substantially enhanced stability for the high-temperature, long-duration conditions amenable to powder-route production of bulk nanostructured tungsten. This nanostructured alloy adopts a heterogeneous chemical distribution that is anticipated by the present theoretical framework but unexpected on the basis of conventional bulk thermodynamics.