Modeling of reactive synthesis in consolidated blends of fine Ni and Al powders

A model is proposed to describe the kinetics of reactive synthesis of NiAl from consolidated Ni-Al fine powder blends for various synthesis heat treatments. The presence of interfacial oxide in the blend and heat exchange between the sample and the environment have been taken into account to simulate the evolution of temperature and phase composition in the blend. A good agreement was obtained between the model calculations and experimental results. The effect of interfacial oxides and of various external parameters (heating rate, heat exchange conditions, powder size, etc.) on the synthesis kinetics was investigated. The model allows to explain the difference in reaction paths (self-propagating synthesis or solid state synthesis) observed in consolidated powder blends, as well as to describe the shape of the differential thermal analysis signal. Based on the results, the disagreement in previously reported data on growth kinetics of aluminides in diffusion structures with different characteristic diffusion distances is discussed. (C) 1998 Elsevier Science S.A. All rights reserved.