REACTION PROCESS AND MODEL SIMULATION OF COMBUSTION SYNTHESIS OF NI3AL INTERMETALLIC COMPOUNDS

The formation mechanism of a Ni3Al intermetallic compound produced by combustion synthesis was investigated by the observation of the reaction process in premixed powder compacts of Ni and Al (Ni : Al = 3 : 1, in atomic ratio). A green compact was vacuum-heated in an electric furnace to cause its thermal explosion reaction. The measurements of sample temperature and the observation of microstructural changes during the reaction process were perfomed. The synthesized products were analyzed by X-ray diffraction and EPMA. It was found that the Al eutectic melt was formed and it surrounded Ni particles at the eutectic temperature in the Ni-Al system. The synthesis reaction was initiated at the interface between the melt and Ni, and the Ni2Al3 layer was shaped m the particles during the combustion sinthesis. The reaction process has been simulated with a spherical shell model which comprises reaction kinetics and heat balance equations. The calculated value obtained by the model was in good agreement with the experimental value. Therefore, the shell model could be applied for the analysis of the present synthesis mechanism. It was evaluated by the model that in the initial stage of combustion synthesis the chemical reaction at the interface between Ni2Al3 and Ni controlled the overall reaction rate of the compound formation, and in the last stage the diffusion of Al in the Ni2Al3 layer was dominant.