Hydrogen absorption and desorption behavior of Zr-based amorphous alloys with a large structurally relaxed amorphous region

Abstract

Abstract A plateau was observed in the P – C isotherm of the amorphous Zr 55 Al 10 Ni 5 Cu 30 alloy for which the temperature region between the glass and crystallization temperature is rather large (Δ T x = T x − T g =83 K). The plateau comprises a hydrogen concentration range from 0.7 to 1.4 mass%H 2 at 573 K and a hydrogen pressure of 1.8 MPa. The existence of the plateau is due to the formation of an amorphous hydride with the approximate composition (Zr 0.55 Al 0.10 Ni 0.05 Cu 0.30 ) 49 H 51 . The amorphous hydride crystallizes in the two stages, namely amorphous hydride→second amorphous phase+ZrH 2 →ZrH 2 +ZrAlCu 2 . The onset temperature for the first-stage reaction decreases from 632 K at C H =1.06 mass% to 615 K at C H =1.34 mass%. It was also found that the first- and second-stage crystallization temperatures correspond well to the T g and T x of the as-quenched amorphous alloy. The change in the atomic mobility seems to play an important role in the decomposition temperature and the dense packing of the amorphous hydride.