The phase diagram and superabundant vacancy formation in Fe–H alloys under high hydrogen pressures

Abstract

In situ XRD measurements at high temperatures and high hydrogen pressures were performed on Fe–H alloys, and in combination with all available data a p(H 2)– T diagram was constructed up to p(H 2)=10 GPa and T=1500 °C. A drastic reduction of the melting point with dissolution of hydrogen, down to 800 °C at 3 GPa, was observed. In the f.c.c. phase, a gradual lattice contraction due to superabundant vacancy formation was found to take place over several hours. The lattice parameter at 784 °C, 4.7 GPa decreased by 6%, which implies that a vacancy concentration as high as 19 at.% was attained.