Kinetics and morphology of the reverse beta ->alpha hydride transformationin thermodynamically open Pd-H system

The kinetics of degassing and reverse beta-->alpha hydride transformation i nitiated in the unstrengthened beta-hydride of Pd in the thermodynamically open Pd-H system is studied. An isothermal kinetic diagram was constructed and its shape was similar to those of transformations in steel during heati ng. With optical microscopy in situ and video-registration methods the morp hology of new alpha-phase precipitations is studied. It is shown that the p rocess of alpha-phase generation in subsurface layers depends on the orient ation of the grain crystal lattice to the surface. alpha-Phase nuclei grow in borders of the grain in, which they were generated. It is shown that hyd rogen macro-stresses may be generated throughout the whole volume of the be ta-hydride sample and they relax by means of grain borders appearance (mutu al grains displacement). During the process of beta-->alpha transformation local internal hydrogen stresses may slow down both degassing and beta-->al pha transformation. (C) 1999 Elsevier Science S.A. All rights reserved.