Molecular dynamics study of deformation and fracture in a tantalum nano- crystalline thin film
L Smith and JA Zimmerman and LM Hale and D Farkas, MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, 22, 045010 (2014).
We present results from molecular dynamics simulations of two nano- crystalline tantalum thin films that illuminate the variety of atomic- scale mechanisms of incipient plasticity. Sample 1 contains approximately 500K atoms and 3 grains, chosen to facilitate study at 10(5) s(-1) strain rate; sample 2 has 4.6M atoms and 30 grains. The samples are loaded in uniaxial tension at deformation rates of 10(5)-10(9) s(-1), and display phenomena including emission of perfect 1/2 < 1 1 1 >-type dislocations and the formation and migration of twin boundaries. It was found that screw dislocation emission is the first deformation mechanism activated at strain rates below 10(8) s(-1). Deformation twins emerge as a deformation mechanism at higher strains, with twins observed to cross grain boundaries as larger strains are reached. At high strain rates atoms are displaced with the characteristic twin vector at a ratio of 3:1 (10(8) s(-1)) or 4:1 (10(9) s(-1)) to characteristic dislocation vectors. Fracture is nucleated through a nano-void growth process. Grain boundary sliding does not scale with increasing strain rate. Detailed analysis of nano-scale deformation using these tools enhances our understanding of deformation mechanisms in tantalum.
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