Dislocation pinning by substitutional impurities in an atomic-scale model for Al(Mg) solid solutions

Abstract

We report our atomic-scale computations for the static depinning threshold of dislocations in Al(Mg) solid solutions. The interaction between the dislocations and the isolated obstacles is studied for different types of obstacle, i.e. single solute atoms situated at different positions, and solute dimers with different bond directions. Part of this work is used to apply different standard analytical theories for solid solution hardening, the predictions of which are finally compared with our direct atomic-scale simulations (AS) for dislocation depinning in random Al(Mg) solid solutions. According to our comparisons, the dislocation statistics in our AS is qualitatively well described by the Mott–Nabarro–Labusch theory. In agreement with earlier results about a different system, namely Ni(Al), the depinning thresholds are similar for the edge and for the screw dislocations.

Keywords:

• dislocation
• hardness
• aluminium alloys
• simulation
• statistical mechanics

Acknowledgements

Dr. David Rodney is gratefully acknowledged for his fruitful remarks.

Notes

Notes

1. The shear modulus is the one for (111) planes μ = (C ₁₁ − C ₁₂ + C ₄₄)/3 while Poisson's ratio is computed from the Voigt average ν = (C ₁₁ + 4C ₁₂ − 2C ₄₄)/(2(2C ₁₁ + 3C ₁₂ + C ₄₄)). Within the EAM model for Al, μ = 30.8 GPa and ν = 0.32.

2. Using the sextic theory presented in 24, we found μ_SB = 31.9 GPa and ν_SB = 0.34 within the EAM model for Al.