In situ atomic-scale observation of twinning-dominated deformation in nanoscale body-centred cubic tungsten

Abstract

Twinning is a fundamental deformation mode that competes against dislocation slip in crystalline solids. In metallic nanostructures, plastic deformation requires higher stresses than those needed in their bulk counterparts, resulting in the 'smaller is stronger' phenomenon. Such high stresses are thought to favour twinning over dislocation slip. Deformation twinning has been well documented in face-centred cubic (FCC) nanoscale crystals. However, it remains unexplored in body-centred cubic (BCC) nanoscale crystals. Here, by using in situ high-resolution transmission electron microscopy and atomistic simulations, we show that twinning is the dominant deformation mechanism in nanoscale crystals of BCC tungsten. Such deformation twinning is pseudoelastic, manifested through reversible detwinning during unloading. We find that the competition between twinning and dislocation slip can be mediated by loading orientation, which is attributed to the competing nucleation mechanism of defects in nanoscale BCC crystals. Our work provides direct observations of deformation twinning as well as new insights into the deformation mechanism in BCC nanostructures.

Atomistic simulations on ductile-brittle transition in ⟨111⟩ BCC Fe nanowires

“…In contrast, all other potentials for BCC Fe predict a degenerate core structure. Similarly, depending on orientation, this potential correctly predicts deformation by twinning and dislocation slip in BCC Fe nanowires 8,9,14,19,20 , which is quite close to the recent experimental observations in ultra-thin BCC W nanopillars 11 . The mechanism of twin nucleation and growth 14,32 , twin boundary as a dislocation source 20,32 , twin migration stress 14,33 , twist boundary structure 34 , accumulation of straight screw dislocations 19 , and various twin-twin interactions 32,33 are in good agreement with those observed experimentally 33,[35][36][37] .…”

Femtosecond X-Ray Diffraction Studies of the Reversal of the Microstructural Effects of Plastic Deformation during Shock Release of Tantalum

“…Furthermore, twinning-detwinning deformation in grains with transverse dimensions of the order of 100-nm (see micrograph in Fig. 1) may be analogous to the cyclic loading-unloading experiments performed on nanopillars [51], suggesting pseudoelastic properties of the nanoscale materials not only on the static, but also on the dynamic timescales.…”

Twinning effects on strength and plasticity of metallic materials

“…57 , 58 In situ nanoindentation studies of NT Al also show that ITBs provide strong barriers to the pileup of dislocations, which results in signifi cant work hardening in NT metals in Al. 38 They also highlight the fi nding of deformation twins in body-centered-cubic (bcc) metals such as W. 59 …”