Complex Precipitation Pathways in Multi-Component Alloys

TL;DR

This paper investigates the complex precipitation pathways in multi-component Al-Zr-Sc alloys, revealing how differing diffusivities lead to inhomogeneous precipitate structures that enhance nucleation and stability.

Contribution

It combines atomic simulations and experimental methods to uncover the inhomogeneous structure of precipitates in Al-Zr-Sc alloys, highlighting the role of diffusivity differences.

Findings

Precipitates have Sc-rich cores and Zr-rich shells.

Enhanced nucleation rate compared to binary alloys.

Higher resistance to Ostwald ripening.

Abstract

One usual way to strengthen a metal is to add alloying elements and to control the size and the density of the precipitates obtained. However, precipitation in multicomponent alloys can take complex pathways depending on the relative diffusivity of solute atoms and on the relative driving forces involved. In Al-Zr-Sc alloys, atomic simulations based on first-principle calculations combined with various complementary experimental approaches working at different scales reveal a strongly inhomogeneous structure of the precipitates: owing to the much faster diffusivity of Sc compared with Zr in the solid solution, and to the absence of Zr and Sc diffusion inside the precipitates, the precipitate core is mostly Sc-rich, whereas the external shell is Zr-rich. This explains previous observations of an enhanced nucleation rate in Al-Zr-Sc alloys compared with binary Al-Sc alloys, along with much higher resistance to Ostwald ripening, two features of the utmost importance in the field of light high-strength materials.