Abstract
“Smaller is stronger” has been commonly observed in cubic structured and hexagonal close-packed (HCP) structured materials. Dislocation starvation phenomenon is highly responsible for the increase of strength at smaller scale in cubic materials. However, by using quantitative in situ transmission electron microscope (TEM) nano-mechanical testing on cylindrical titanium nano-pillars with diameters of ~150 nm but varied orientations and three dimensional dislocation tomography, we found that dislocation nucleation and multiplication dominate the plastic deformation of the nano-pillars with no sign of dislocation starvation, resulting in much better ability of dislocation storage and plastic stability of HCP structured materials at extremely small scale.
Highlights
“Smaller is stronger” has been commonly observed in cubic structured and hexagonal close-packed (HCP) structured materials
It has been found that there is a strong size effect which shows a reproducible trend that “smaller is stronger” as the diameter of the samples reduce from conventional sizes into micrometer and submicron regime in single crystal body-centered cubic (BCC) and face-centered cubic (FCC) metals, as well as hexagonal close-packed (HCP) metals[7,8,9,10,11,12,13,14]
The easy glide of dislocations in small volumes makes dislocation storage difficult and usually facilitates strain bursts. Since both the driving force—the image stress and the critical stress needed for dislocation self-multiplication increase with decreasing size, as the external size is reduced to a critical value (~200 nm for FCC and BCC samples) the specimen eventually loses the ability for dislocation storage and the entire structure catastrophically collapses under loading
Summary
Peng Huang & Qian Yu “Smaller is stronger” has been commonly observed in cubic structured and hexagonal close-packed (HCP) structured materials. The easy glide of dislocations in small volumes makes dislocation storage difficult and usually facilitates strain bursts Since both the driving force—the image stress and the critical stress needed for dislocation self-multiplication increase with decreasing size, as the external size is reduced to a critical value (~200 nm for FCC and BCC samples) the specimen eventually loses the ability for dislocation storage and the entire structure catastrophically collapses under loading. The [0001] oriented titanium and magnesium single crystals were studied in which the activation of dislocation slip would be more difficult since the shear stress barely resolved onto the easy glide systems Under this extreme condition, the uncommon 〈c + a〉 dislocations’ activities were observed in ~200 nm sized samples as well[19]. Dislocation starvation was not observed, which was completely different from FCC and BCC metals
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