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Abstract Stacking fault tetrahedron (SFT) is a kind of 3D defect commonly seen in the irradiated metals, which could significantly impact the plasticity of metals. Using molecular statics (MS) and molecular dynamics (MD) methods, different sizes and shapes of stacking-fault-tetrahedron-like structures (SFTLS) are created in a single copper crystal by considering different sizes and shapes of vacancy clusters on the (111) plane. We analyze the dislocation evolution mechanisms and variations of formation energies of SFTLS with different shapes during their formation processes. Then, we discuss the vacancy formation energy distribution in the vicinity of a SFTLS as well as the variation of the lowest vacancy formation energy vs the size of SFTLSs. Finally, we analyze the deformation mechanism and yield stress variation of single copper crystal embedded with a SFTLS of different sizes. It is found that SFTLS forms through the process of vacancy cluster collapse, Frank loop dissociation and formation of SFTLS edge due to the intersection of Shockley partial dislocations. The lowest vacancy formation energy site in a SFTLS changes as the size of SFTLS increases, and lowest vacancy formation magnitudes are strongly connected to the transition between stable, metastable and unstable states of SFTLS. Moreover, marked size effect in lowest vacancy formation variation is seen in the stable state of no-apex SFTLS. Furthermore, there are two dislocation nucleation mechanisms corresponding to the incipient plasticity of single crystal with a SFTLS under shear, i.e. glide of Shockley partials on the tilt (111) planes and dissociation of stair-rod dislocations on the basal plane of a SFTLS. The yield stress of single crystal with a SFTLS basically decreases as increasing the size of SFTLS.
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Received: 24 January 2020
Published: 28 December 2020
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2020, Vol. 41 
