Unusual effect of high pressures on phase transformations in Ni$_{62}$Nb$_{38}$ alloy

TL;DR

This study maps the extensive pressure-temperature phase diagram of Ni$_{62}$Nb$_{38}$ alloy, revealing unique high-pressure effects on phase transformations and identifying conditions for phase coexistence, with implications for understanding glass formation.

Contribution

First comprehensive phase diagram of Ni$_{62}$Nb$_{38}$ alloy across wide pressures and temperatures, including phase separation conditions at ultra-high pressures.

Findings

Good agreement with experimental liquidus and glass transition temperatures at atmospheric pressure.

Detailed phase diagram for pressures above 10^7 atm.

Identification of phase separation conditions for liquid Nb and crystalline Ni.

Abstract

Binary Ni$_{62}$Nb$_{38}$ alloy belongs to the unique class of binary off-eutectic systems, which are able to form a bulk glassy state [L. Xia et al., J. Appl. Phys. 99 (2006) 026103]. In the present work, the ($p$, $T$) phase diagram of Ni$_{62}$Nb$_{38}$ alloy was first determined for a wide thermodynamic range with temperatures from $300$\,K to $6000$\,K and with pressures from $1$\,atm to $1.2\times10^7$\,atm. For this thermodynamic range, elements of the phase diagram such as the liquid-crystal coexistence line and the glass transition line are defined. Our results reveal good agreement between the simulation results and the known experimental values of the liquidus temperature and the glass transition temperature for the isobar $p=1$\,atm. The phase diagram is detailed for pressures greater than $1\times10^{7}$\,atm. For the first time, the phase separation conditions at which the liquid Nb and crystalline Ni phases coexist in the system were determined.