SYNTHESIS OF NANODISPERSED PHASES DURING RAPID SOLIDIFICATION AND CRYSTALLIZATION OF GLASSES IN TI75NI25 ALLOYS

The formation of the metallic glass and crystalline phases and related microstructures and the decomposition behavior of rapidly solidified Ti75Ni25 alloys obtained under different processing conditions have be en investigated in detail. The competition between glass transition an d nucleation of beta-Ti during rapid solidification leads to the possi bility of synthesizing the nanocomposites of beta-Ti and glass. Additi onally, it is shown that the presence of a small amount of Si also pro motes simultaneous nucleation of fine Ti2Ni intermetallic compound. Th ermodynamic calculation of the metastable phase diagram indicates the presence of a metastable eutectic reaction between alpha-Ti and Ti2Ni. Evidence of this reaction at lower cooling rates has been presented. On heating, the glass decomposes through this reaction. Finally, on th e basis of understanding of the microstructural evolution during decom position, a new approach has been adopted to synthesize a nanodisperse d composite of alpha-Ti in the crystalline Ti2Ni matrix with a narrow size distribution by controlling the devitrification heat treatment of the metallic glass.