Mechanism of the β to ω phase transformation in shock compressed Zr-Nb alloys

HJ Li and L Zhao and XD Ding and HX Zong and T Lookman and J Sun, PHYSICAL REVIEW B, 110, 134105 (2024).

DOI: 10.1103/PhysRevB.110.134105

In beta-Zr alloys, the mechanism of omega phase formation and its interaction with deformation twinning remain subjects of debate, particularly under high strain-rate loading. In this paper, we investigate the beta -> omega phase transformation in shock loaded Zr-10Nb (at. %) single crystals using molecular dynamic simulations. Our findings indicate a direct connection between deformation-induced phase transformation and the spatial arrangement of Nb atoms. The initiation of both the omega phase and 112(beta) < 111 >(beta) deformation twins is mediated by the formation of 1/6 < 111 >(beta) partial dislocations (PDs). It is the local Nb composition that dictates the more energetically favorable transition path toward the subsequent formation of the omega phase or deformation twins. Remarkably, we identify a previously unknown mechanism for the beta -> omega transformation. This process begins with the emergence of 1/6 < 111 >(beta) partials, separated by a few atom layers, followed by atomic shuffling between the PDs. Our findings outline the importance of compositional fluctuation in the transformation mediated plasticity in metastable Zr-based alloys.

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