Reactive powder metallurgy offers an interesting alternative technology for the production of nickel silicide based intermetallic materials. The heat release during reaction and the microstructure of the product can be controlled by mechanical alloying of the reactants. In order to determine the optimal processing conditions for mechanical alloying, the relationships among the processing conditions, the microstructure of the mechanically alloyed powder and the reaction mechanism have been identified. This was done with the aid of a mathematical description of the mechanical alloying process in a planetary ball mill, which allowed the prediction of the hardness and deformation of the material as a function of the milling conditions. Experimental verification under a broad range of conditions shows a good agreement between the measured and predicted hardness values. The relation between microstructure and milling conditions was quantitatively expressed as an inverse exponential relation between the calculated strain and the crystallite size of the material. The mechanism of synthesis of the Ni-3(Si, Ti) phase in the mechanically alloyed powder was studied. It is shown that the transition of a high-temperature self propagating reaction in the unmilled powder to a low temperature solid-state reaction depends on the crystallite size of the milled powder. By using the relations among milling conditions, microstructural characteristics and reaction behavior of the mechanically alloyed powder, milling maps with "equivalent milling conditions" were calculated. These milling maps represent the sufficient conditions to obtain the desired level of strain in the material. By using these maps, the experimental work for optimization of the mechanical alloying process can be greatly reduced. (C) 1998 Acta Metallurgica Inc.