Molecular Dynamics Simulation of the Effects of Crystal Orientation and Grain Boundary Misorientation Angle on the Nano-Crack Growth

O Nejadseyfi and A Shokuhfar, JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 11, 2199-2207 (2014).

DOI: 10.1166/jctn.2014.3627

In this paper, crack propagation mechanisms are investigated in single crystal and bicrystal FCC aluminum. The first part of this paper deals with the assessment of the crack initiation and growth under mode I loading condition by altering the crystal orientation. In the second part, the influence of the presence of grain boundary is analyzed by adding low-angle symmetric tilt boundary (Sigma 1(100)) and high-angle symmetric tilt boundaries (Sigma 5 < 210 >/(100), Sigma 5 < 310 >/(100), Sigma 17 < 410 >/(100) and Sigma 13 < 510 >/(100). The results showed that in single crystals, the crack was extended through void nucleation, void growth and coalescence. More precise examinations showed that the void nucleation region was mostly dependent on the crystal orientation. Although octahedral slip systems of type 111< 110 > were dominant slip system in nearly all cases, when the crystal was oriented along 110 direction, both octahedral slip systems of type 111< 110 >, and rare cubic slip systems of type 100< 110 > were activated. In the second part of the paper, Low-angle symmetric tilt grain boundary, Sigma 1(100), and high-angle symmetric tilt grain boundaries of Sigma 5 < 210 >/(100), Sigma 5 < 310 >/(100), Sigma 17 < 410 >/(100) and Sigma 13 < 510 >/(100) were generated in the distance of 2 nm from the crack tip. Assessment of the stress-strain graphs in these cases showed that the peak value of stress with and without crack was very close to each other in the cases of Sigma 1(100) and Sigma 13 < 510 >/(100), in which the grain boundary migration was remarkable. So, in these cases shear- coupled migration process provided an effective toughening mechanism which allowed the cracked bicrystal to achieve a superior strength which was very close to the uncracked samples. But in other cases as the grain boundary migration was not apparent, a meaningful difference in the value of peak stress of cracked and uncracked samples was observed.

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