In situ TEM study of twin boundary migration in sub-micron Be fibers. (1st September 2015)

• Record Type: Journal Article
• Authors: Mompiou, F.; Legros, M.; Ensslen, C.; Kraft, O.
• Is Part Of: Acta materialia. Volume 96(2015)
• Page Start: 57
• Page End: 65
• Publication Date: 2015-09-01
• Subjects: In situ TEM -- Twinning -- Fibers -- Dislocations -- Plasticity; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2015.06.016
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Deformation twinning in hexagonal crystals is often considered as a way to palliate lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in situ in a transmission electron microscope (TEM) deform by a { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 0 〉 twin thickening. The propagation speed of the twin boundary seems to be entirely controlled by the nucleation of twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of twinning dislocations. We demonstrate that the activation volume ( V ) associated with the twin boundary propagation can be retrieved from the measure of the twin boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of V ≈ 1.6 ± 0.4 × 10 - 28 m 3 is comparable to the value expected from surface nucleation.