Ductility mechanisms in complex concentrated refractory alloys from atomistic fracture simulations

TL;DR

This study uses atomistic fracture simulations with machine-learning interatomic potentials to analyze how compositional complexity influences damage tolerance and fracture mechanisms in refractory alloys.

Contribution

It introduces a new MLIP for NbTaTiHf and demonstrates how alloying alters fracture modes and enhances ductility in complex refractory alloys.

Findings

NbMoTaW shows increased dislocation activity despite brittleness.

Nb45Ta25Ti15Hf15 exhibits higher crack resistance due to dislocation accumulation.

Fracture mechanisms vary significantly with alloy composition.

Abstract

The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations, contrasting behavior in elemental Nb with that in brittle NbMoTaW and ductile Nb45Ta25Ti15Hf15. We employ machine-learning interatomic potentials (MLIPs), including a new MLIP developed for NbTaTiHf, in atomistic simulations of crack tip extension mechanisms based on analyses of atomistic fracture resistance curves. While the initial behavior of sharp cracks shows good correspondence with the Rice theory, fracture resistance curves reveal marked changes in fracture modes for the complex alloys as crack extension proceeds. In NbMoTaW, compositional complexity appears to promote dislocation nucleation relative to pure Nb, despite theoretical predictions that the alloy should be relatively more brittle. In Nb45Ta25Ti15Hf15, alloying not only changes the fracture mode relative to elemental Nb, but promotes dislocation accumulation at the crack tip, leading to higher resistance to crack propagation.