Role of irradiation induced defects in altering the micro-mechanical response of Zr domains during nano indentation: A molecular dynamics study

V Singh and NN Kumar and KVM Krishna and G Sharma and R Tewari and GK Dey, COMPUTATIONAL MATERIALS SCIENCE, 161, 151-162 (2019).

DOI: 10.1016/j.commatsci.2019.01.036

In the present study, the plastic flow behavior of Zr at 300 K in the presence of defects i.e. self-interstitials, vacancies and voids, which generally form during irradiation, has been investigated by molecular dynamics (MD) simulation of nano-indentation. For the purpose of comparison, a perfect defect-free domain was also probed under similar loading conditions. During nano-indentation various dislocation activities, i.e. nucleation, interactions, locking etc., involved during a typical loading cycle, were distinctly captured. This study has clearly demonstrated that the nature of defects present in the domain influences the dislocation activities during nano-indentation. Using Schmid factor calculation, it is shown that the nucleation of dislocation in all the domains, except the domain containing self- interstitials, occurs only along the directions of maximum resolved stress. In the case of domain containing self-interstitials, difference in the behavior was shown due to the presence of self-interstitials loops, which influenced the state of stress beneath the region of nano- indenter. The cyclic nano-indentation responses of all the domains were quantified in terms of the value of the nano-hardness in each loading stage. In all cases, except in the case of vacancies containing domain, the value of nano-hardness tends to saturate with the increasing number of cycles. In the case of domain containing vacancies the continuous drop in the nano-hardness was observed due to the formation of defect free channels resulting in continuous softening of domain. In the present study the role of vacancies over dislocation loops in the formation of these channels has been emphasized. The current MD simulation is the first such study which shows the feasibility of localized channel formation in the presence of large concentration of vacancies during cyclic nano-indentations.

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