Dynamic mechanisms of strengthening and softening of coherent twin boundary via dislocation pile-up and cross-slip

Abstract

Although cross-slip strongly affects the deformation of polycrystalline materials, the phenomenon is rarely studied in twinned face centered cubic (FCC) metals. Here we performed in-situ TEM nanoindentation on a twinned nickel bi-crystal. Multiple pile-ups were generated, with the first dislocations pinned at a coherent twin boundary (CTB) and multiple following dislocations cross-slipping within the matrix. Stress calculation revealed that the cross-slip events are made possible by the CTB, the first dislocations, and the favorable shear stress created jointly by external stress and dislocation interaction. These cross-slip events reduce tip stress and soften the material until inter-grain plasticity is eventually activated.

IMPACT STATEMENT

In-situ TEM nanoindentation reveals the characteristics of dislocation pinning, pile-ups and cross-slip along the twinning boundary in a twinned FCC metal for the first time.

GRAPHICAL ABSTRACT

KEYWORDS:

• Coherent twin boundary
• dislocation pinning
• pile-up
• cross-slip
• in-situ TEM nanoindentation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Key R & D Program of China [grant number 2021YFA1200201], the Natural Science Foundation of China [grant numbers 51988101, 91860202, 52071003], Beijing Municipal Education Commission Project [grant numbers PXM2020-014204-000021 and PXM2019-014204-500032], Beijing Outstanding Young Scientists Projects [grant number BJJWZYJH01201910005018], Beijing Natural Science Foundation (Z180014), ‘111’ project (DB18015), Doctoral Research and Innovation Program of China People’s Police University [grant number BSKY2019001], Beijing Nova Program (Z211100002121170).