The equation of state of solid nickel aluminide

TL;DR

This paper combines theoretical calculations and experimental shock wave measurements to determine the comprehensive equation of state for solid NiAl, validating models with experimental data and exploring its compression behavior under high pressure.

Contribution

It presents a thermodynamically complete equation of state for NiAl, integrating ab initio calculations with shock experiments to improve understanding of its compression and shock response.

Findings

The Rose compression curve matches ab initio data in compression but deviates in expansion.

The static and shock compression data for NiAl are consistent with the theoretical model.

The experiments reveal the effects of elasticity and plastic flow during shock loading.

Abstract

The pressure-volume-temperature equation of state of the intermetallic compound NiAl was calculated theoretically, and compared with experimental measurements. Electron ground states were calculated for NiAl in the CsCl structure, using density functional theory, and were used to predict the cold compression curve and the density of phonon states. The Rose form of compression curve was found to reproduce the ab initio calculations well in compression but exhibited significant deviations in expansion. A thermodynamically-complete equation of state was constructed for NiAl. Shock waves were induced in crystals of NiAl by the impact of laser-launched Cu flyers and by launching NiAl flyers into transparent windows of known properties. The TRIDENT laser was used to accelerate the flyers to speeds between 100 and 600m/s. Point and line-imaging laser Doppler velocimetry was used to measure the acceleration of the flyer and the surface velocity history of the target. The velocity histories were used to deduce the stress state, and hence states on the principal Hugoniot and the flow stress. Flyers and targets were recovered from most experiments. The effect of elasticity and plastic flow in the sample and window was assessed. The ambient isotherm reproduced static compression data very well, and the predicted Hugoniot was consistent with shock compression data.