HYDROGEN SORPTION AND HYDROGEN-INDUCED PHASE-SEPARATION IN A NEARLY EQUIATOMIC NI-ZR AMORPHOUS ALLOY

The influence of hydrogen on some physical properties and on the microstructure of a nearly equiatomic, melt-quenched Ni-Zr amorphous alloy was investigated. Hydrogen absorption from the gas phase at 190-degrees-C and 35-40 atm pressure was measured by weight as a function of the charging time. Considerable hydrogen absorption occurred only for charging times around 10 h and was completed within a few hours. The hydrogen content remained constant for a hydrogen-to-metal ratio of about one for prolonged charging. The room-temperature thermopower changed considerably upon hydriding and a local thermopower probe revealed that the activation time varies considerably along the ribbon length. It was found that, during further heat treatment in a hydrogen gas atmosphere after a hydrogen-to-metal ratio of approximately one was reached, the magnetic state of the amorphous Ni-Zr samples changed progressively from paramagnetic to super-paramagnetic. 4lusters, which were nickel-rich segregations induced by the hydriding process, were determined by magnetic and scanning transmission electon microscopic measurements. After desorbing hydrogen at elevated temperatures, magnetic measurements indicated the disappearance of the superparamagnetic clusters.