Mechanical alloying of the FeNi–Ag system

The Fe–Ni–Ag system is of particular interest for its potential applications as soft magnetic granular material with small magnetic grains embedded in a non-magnetic metal matrix. Under equilibrium conditions: Fe–Ag and Ni–Ag are immiscible and Fe–Ni shows complete solubility. These materials are particularly important for magnetoresistivity properties. The properties of these alloys are closely related to their microstructure; therefore, a detailed study of the transformations occurring during milling was undertaken using pre-alloyed Fe x Ni 100− x ( x = 30, 50 and 70) further milled with different Ag content to give the following alloys compositions (Fe x –Ni 100− x ) 100− y Ag y ( y = 5, 20, 60). Consolidation of the mechanically alloyed powders by sintering at 950 °C was performed. Morphological and structural characterization of the sintered powders was carried out by scanning and transmission electron microscopy and X-ray diffraction. Fe 30Ni 70 and Fe 50Ni 50 formed ordered FeNi 3 compound. Fe 70Ni 30 showed the formation of a mixture of γ-(Fe,Ni) and α-Fe(Ni) solid solutions. The mixture of these systems with Ag showed the metal solid solutions surrounded by Ag islands of Fe x Ni y –Ag, There was also evidence of Ag diffusing into the γ-(Fe,Ni). High Ag content (60%) shows formation of islands of FeNi surrounded by Ag. Sintering is always improved with the Ag content.