Contributions of Al and Ni segregation to the interfacial cohesion of Cu-rich precipitates in ferritic steels

TL;DR

This study uses first-principles calculations to analyze how aluminium and nickel segregation at interfaces affects the cohesion of copper-rich precipitates in ferritic steels, impacting steel embrittlement.

Contribution

It reveals the contrasting effects of aluminium and nickel segregation on interfacial cohesion, advancing understanding of steel embrittlement mechanisms.

Findings

Aluminium segregation enhances interfacial cohesion.

Nickel segregation reduces interfacial cohesion.

Nickel increases the ductile-brittle transition temperature.

Abstract

We characterise the influence of the segregation behaviours of two typical alloying elements, aluminium and nickel, on the interfacial cohesive properties of copper-rich precipitates in ferritic steels, with a view towards understanding steel embrittlement. The first-principles method is used to compute the energetic and bonding properties of aluminium and nickel at the interfaces of the precipitates and corresponding fracture surfaces. Our results show the segregation of aluminium and nickel at interfaces of precipitates are both energetically favourable. We find that the interfacial cohesion of copper precipitates is enhanced by aluminium segregation but reduced by nickel segregation. Opposite roles can be attributed to the different symmetrical features of the valence states for aluminium and nickel. The nickel-induced interfacial embrittlement of copper-rich precipitates increase the ductile-brittle transition temperature (DBTT) of ferritic steels and provides an explanation of many experimental phenomena, such as the fact that the shifts of DBTT of reactor pressure vessel steels depend the copper and nickel content.