[SY-B6] Novel Deformation Mechanism of Helium Irradiated Copper
The workability and ductility of metals usually degrade with exposure to irradiation, hence the phrase “radiation damage”. Here, we found that Helium (He) radiation can actually enhance the room-temperature deformability of submicron-sized copper. In particular, Cu single crystals with diameter of 100 nm to 300 nm and containing numerous pressurized sub-10 nm He bubbles, become stronger, more stable in plastic flow and ductile in tension, compared to fully dense samples of the same dimensions that tend to display plastic instability (strain bursts). The sub-10 nm He bubbles are seen to be dislocation sources as well as shearable obstacles, which promote dislocation storage and reduce dislocation mean free path, thus contributing to more homogeneous and stable plasticity. Failure happens abruptly only after significant bubble coalescence. Furthermore, we discover that the helium bubble not only can coalesce with adjacent bubbles, but also can split into several nanoscale bubbles under tension. Alignment of the splittings along a slip line can create a bubble-free-channel, which appears softer, promotes shear localization, and accelerates the failure in shearing-off mode. Detailed analyses unveil that the unexpected bubble fragmentation is mediated by the combination of dislocation cutting and internal surface diffusion, which is an alternative micro-damage mechanism of helium irradiated copper besides the bubble coalescence. These results shed light on plasticity and damage developments in metals. Ref. PRL 117 (2016) 515501, Nano Lett.16 (2016)4118 and Nano Lett. 17 (2017) 3725.