Symposium SF07—In Situ Material Performance and Dynamic Structure Characterization Under Coupled Extremes

Daniel Kiener, Montanuniversity Leoben

Size Affected Toughening and Strain Rate Sensitivity of Silicon

Written by Henry Quansah Afful

It is a well-known phenomenon that nanostructured materials are much stronger than their bulk counterparts but this usually limits their fracture toughness. Can we emit dislocations that will blunt the crack tip and thereby increase the fracture toughness in these nanostructured materials? Kiener demonstrates this phenomenon in nanostructured silicon (Si) using in situ transmission electron microscope (TEM) at room temperature. Kiener created a notch in the material along some crystallographic orientation to act as a stress concentration site. TEM images reveal the nucleation of dislocations from the crack tip in <250 nm-thick Si which blunted the crack tip and increased the fracture toughness by a factor of 3 from what is observed in bulk Si. Dark field mode in TEM revealed the absence of these dislocations prior to the bending test proving that these were formed during the test. The presence of this intrinsic toughening mechanism in Si makes it more damage-tolerant and useful for microelectromechanical devices.