TEM STUDY OF B2-RICH NI-AL FILM(L1(2) DECOMPOSITION IN A NANOSCALE NI)

The decomposition of a free-standing monophase B2 Ni62.5Al37.5 thin fi lm with nanoscale dimensions, for thickness as well as lateral grain s ize, is investigated by in situ and subsequent high resolution transmi ssion electron microscopy. The atomic structure, microstructure and te xture are unchanged until a temperature of 450 degrees C is reached ab ove which a two-phase mixture of B2 + L1(2) is formed. The predominant texture of the B2 film is inherited in the L1(2) grains and even impr oved during the passage of the transformation front. As a result many small angle tilt boundaries exist in between neighbouring [001] L1(2) grains. Around 1000 degrees C some of the L1(2) grains grow in thickne ss forming microcrystals and using material from nearby grains thus de teriorating the integrity of the film. Occasionally also fcc Ni microc rystals with up to 15 at.% disordered Al are observed. (C) 1998 Elsevi er Science S.A. All rights reserved.