FORMATION OF NANOSTRUCTURAL MATERIALS INDUCED BY MECHANICAL PROCESSINGS

Mechanical alloying (MA) was firstly developed to synthesize metallic matrix composite by mechanically incorporating preformed oxide and or carbide particles into a metallic matrix. A consecutive compaction pro cess is applied to obtain bulk materials. During MA, powders are repea tedly welded, fractured and rewelded in a high energy mill leading to an intimate mixing on a nano/micro-scale with the possible formation o f far from equilibrium phases. The versatility of MA is well known; hi gh volume, low energy mills can be used to commercially produced dispe rsion strengthened Al, Ni and other transition metal alloys. Various i ntermetallics and inorganic compounds (amorphous and/or nanocrystallin e) have been synthesized by using higher energy mills which have been specially developed in some cases. Mechanical alloying, it appears, as suggested by T.H. Courtney et al., is the Alladin's lamp of powder pr ocessing. All the published works have shown that the reaction and end products of the MA process strongly depend on the milling conditions. As a consequence, it is obvious that an improved understanding of the dynamics of MA process is required to gain a full appreciation of the industrial potential of the technique for synthesizing materials. Rec ently, M. Abdellaoui and E. Gaffet have shown that the crystal to amor phous phase transition (at least in the case of the model Ni,,Zr,) onl y depends on the injected mechanically power, allowing a direct compar ison among experiments performed using distinct type of milling appara tus (planetary milling machine, horizontal apparatus). An alternative method has been recently proposed by N. Malhouroux-Gaffet and E. Gaffe t, for the solid state synthesis of disilicide powders exhibiting a wi de contamination during the direct MA preparation: the mechanically ac tivated annealing process (M2AP). Such a M2AP method has been applied to the synthesis of FeSi2, MoSi2, WSi2 compounds. Such a method appear s as being a well suitable one for the low temperature synthesis of re fractory nanomaterials. Recent applications have been successfully per formed to mechanically activated sintering (MAS).