Shear band mediated ω phase transformation in Nb single crystals deformed at 77 K

Abstract

Phase transformation is rare in pure body-centered cubic (BCC) metals due to the associated high energy barrier. Here, omega (ω) phase transformation in single-crystal niobium (Nb) under compression at 77 K was studied by atomistic characterization and density functional theory (DFT) calculation. The ω phases were found to nucleate preferentially at the boundaries of 112 shear bands, via a sequence of BCC-to-ω structural transformation induced by shear stress. Theoretically, calculations reveal that the formation of a shear transition region can reduce the energy barrier of BCC-to-ω phase transformation. These findings provide insights into the phase transformation involved in the cryogenic deformation of bulk BCC metals.

IMPACT STATEMENT

Atomistic characterization reveals the structural evolution of shear band mediated ω phase transformation in single-crystal Nb at the atomic scale, where a finite shear distortion of the lattice can greatly reduce the associated transformation barrier.

KEYWORDS:

• Body-centered cubic
• niobium
• ω phase
• shear band
• BCC-to-ω phase transformation

Disclosure statement

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

Additional information

Funding

J.W. acknowledges the support of the National Key R&D Program of China [grant number 2018YFB2000704], and the National Natural Science Foundation of China [grant number 51771172], [grant number 52071284]. H.Z. acknowledges financial support from the National Natural Science Foundation of China [grant number 11902289], [grant number 12172324].