MICROSTRUCTURE EVOLUTION OF MECHANICAL ALLOYED NI-24 AT PERCENT SI

Nickel and silicon powders, of average composition Ni3Si, were mechani cal alloyed in a high energy ball mill. The severe plastic deformation produced by mechanical milling induced transformations with increasin g milling time as follows: mixture of elemental Ni and Si powder --> f .c.c. solid solution --> nanocrystalline f.c.c. The structural evoluti on with milling time was followed by X-ray diffraction, differential s canning calorimetry (DSC), and transmission electron microscopy (TEM). Complete f.c.c. solid solution occurred at a milling time of 4 h and the saturated Delta H (by DSC) peak in the range of estimated enthalpy even after 24 h milling. The similarity of the mechanism of structura l development by mechanical alloying of the Ni76Si24 powder mixture, a nd by mechanical milling of Ni76Si24 compound was also investigated in this study.