Slip energy barriers in aluminium and implications for ductile-brittle behaviour

Abstract

We conisder the brittle versus ductile behavior of aluminum in the framework of the Peierls-model analysis of dislocation emission from a crack tip. To this end, we perform first-principles quantum mechanical calculations for the unstable stacking energy γus of aluminum along the Shockley partial slip route. Our calculations are based on density functional theory and the local density approximation and include full atomic and volume relaxation. We find that in aluminum γus = 0.224 J/m 2 . Within the Peierls-model analysis, this value would predict a brittle solid which poses an interesting problem since aluminum is typically considered ductile.The resolution may be given by one of three possibilites: (a) Aluminum is indeed brittle at zero temperature, and becomes ductile at a finite temperature due to motion of pre-existing dislocations which relax the stress concentration at the crack tip. (b) Dislocation emission at the crack tip is itself a thermally activated process. (c) Aluminum is actually ductile at all temperatures and the theoretical model employed needs to be significantly improved in order to resolve the apparent contradiction.

Link between structural and mechanical stability of fcc- and bcc-based ordered Mg–Li alloys

“…Our predicted elastic constants were calculated at equilibrium lattice constants rather than the experimental values, hence led to slight difference from experimentally determined elasticity. This may be ascribed to the elastic constants being sensitive to the lattice constant of the crystal [33].…”

Energetics of hydrogen impurities in aluminum and their effect on mechanical properties

“…14 The values of ␥ GSF for pure Al have been published elsewhere. 15,16 In the present work we have repeated these calculations to obtain a consistent set of numbers with the computational parameters and methodology adopted here. The values of the important configurations obtained by the present calculations are: ␥ us ϭ0.182 J m Ϫ2 , and ␥ sf ϭ0.134 J m Ϫ2 , both for hϭ0.…”

Peierls–Nabarro model for dislocations in MgSiO3post-perovskite calculated at 120 GPa from first principles

“…The simplest approach to infer the relative resistance of the slip systems is to determine the ideal shear stress τ max introduced above [13,[42][43][44]. The values of τ max are presented in Table 2.…”