The first principles and experimental study of equilibrium and non-equilibrium low-temperature phases of Nb50Ru50 alloy

Abstract

The equilibrium and non-equilibrium low-temperature phases of Nb50Ru50 alloy have been investigated using ab initio calculations (thermodynamic, elastic, and electronic properties) in conjunction with experimental microstructural and phase analyses. Low-temperature phases in Nb50Ru50 alloy originate from the transformation of tetragonal L10 phase at 750 °C, which potentially makes it useful for designing high-temperature shape memory alloys. Current results showed that the monoclinic phase P2m is the most energetically stable under equilibrium conditions, and this is complemented by the absence of negative frequencies in the phonon dispersion curves. However, negative frequencies were observed on the orthorhombic phase Cmmm, indicating that it is a metastable martensite phase. Therefore, two low-temperature phases of Nb50Ru50 have been determined, namely P2m and Cmmm. This forms the basis for further designing of the alloy with superior shape memory properties since P2m is softer and exhibits lower symmetry compared to the brittle L10 phase.