Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale
In mechanical deformation of crystalline materials, the critical resolved shear stress (CRSS; τ[subscript CRSS]) is the stress required to initiate movement of dislocations on a specific plane. In plastically anisotropic materials, such as Mg, τ[subscript CRSS] for different slip systems differs gre...
| Main Authors: | , , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
National Academy of Sciences (U.S.)
2014
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| Online Access: | http://hdl.handle.net/1721.1/85911 https://orcid.org/0000-0002-0201-9333 https://orcid.org/0000-0002-7841-8058 |
| Summary: | In mechanical deformation of crystalline materials, the critical resolved shear stress (CRSS; τ[subscript CRSS]) is the stress required to initiate movement of dislocations on a specific plane. In plastically anisotropic materials, such as Mg, τ[subscript CRSS] for different slip systems differs greatly, leading to relatively poor ductility and formability. However, τ[subscript CRSS] for all slip systems increases as the physical dimension of the sample decreases to approach eventually the ideal shear stresses of a material, which are much less anisotropic. Therefore, as the size of a sample gets smaller, the yield stress increases and τ[subscript CRSS] anisotropy decreases. Here, we use in situ transmission electron microscopy mechanical testing and atomistic simulations to demonstrate that τ[subscript CRSS] anisotropy can be significantly reduced in nanoscale Mg single crystals, where extremely high stresses (~2 GPa) activate multiple deformation modes, resulting in a change from basal slip-dominated plasticity to a more homogeneous plasticity. Consequently, an abrupt and dramatic size-induced “brittle-to-ductile” transition occurs around 100 nm. This nanoscale change in the CRSS anisotropy demonstrates the powerful effect of size-related deformation mechanisms and should be a general feature in plastically anisotropic materials. |
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