The effect of surface step and twin boundary on deformation twinning in nanoscale metallic systems

• Published in: Computational materials science 2018-04, Vol.145, p.116-125
• Main Authors: Béjaud, R., Durinck, J., Brochard, S.
• Format: Article
• Language: English
• Subjects: Acoustics; Automatic; Biomechanics; Chemical Sciences; Deformation twins; Dislocations; Electric power; Electromagnetism; Engineering Sciences; Fluid mechanics; Material chemistry; Materials and structures in mechanics; Mathematical Physics; Mechanics; Metallic film; Molecular dynamics simulations; Physics; Polymers; Quantum Physics; Reactive fluid environment; Surface step; Thermics; Twin boundary; Vibrations
• ISSN: 0927-0256; 1879-0801
• DOI: 10.1016/j.commatsci.2017.12.035

[Display omitted] •Surface steps are correlated with thicker twins ensuing from a lower yield strength.•A coherent twin boundary is a strong barrier to newly nucleated twins propagation.•Twin-twin interaction yields Lomer dislocations which can produce new twins.•In the absence of volume defect the twin size depends strongly on the surface relief.•In the presence of an initial coherent twin boundary this dependency is lost. The effect of surface step and twin boundary on the mechanical twinning process in nanoscale face-centred cubic metallic films was studied using atomistic simulations. Aluminium was considered as a model material but comparisons were made with silver and copper. Surface steps were identified as privileged sites for twin nucleation at lower stresses, leading to the formation of only one large twin in defect-free films. In presence of a coherent twin boundary which acts as a strong barrier to the propagation of dislocations, the extension of nucleated twins is much more limited but the density of secondary twin boundaries is found higher. The key role played by Lomer dislocations, resulting from the interaction between incipient twins and the coherent twin boundary, on the nucleation of new twins was demonstrated. These findings shed light on some elementary mechanisms that can be involved in the elaboration of nanotwinned materials with interesting mechanical properties.