Enhancing the stability of the ω phase of zirconium alloys via local interlayer twists

HJ Li and L Zhao and HX Zong and XD Ding and T Lookman and J Sun and GJ Ackland, PHYSICAL REVIEW B, 107, 184117 (2023).

DOI: 10.1103/PhysRevB.107.184117

The addition of solute provides an effective means to alter the stability of phases in metallic materials. This is particularly true for the metastable t omega phase in Ti- and Zr-based alloys; however, the underlying mechanism remains inconclusive. In the present work, we show that the omega - beta phase-transformation process can be hindered to stabilize the omega phase over a wide temperature and pressure range. This is demonstrated by molecular dynamics simulations of Zr-Nb alloys. In particular, we show that Nb dopants lead to the formation of a defect structure in the Zr-omega phase, i.e., there is a corotation of six atoms in the 0002 plane by 30 degrees along the c axis of the omega lattice. We refer to this as a local interlayer twist (LIT). The LITs are energetically preferred within Nb-rich regions and can interlock omega lattices, thus retarding the omega - beta phase transformation. Furthermore, our density-functional theory calculations suggest that this mechanism should work in Zr- and Ti-based alloys with small solute atoms. The findings enrich our understanding of complex phase- transformation kinetics in alloys.

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