Mechanical Alloying was developed in the 1970's at the International Nickel Co. (INCO) as a technique for dispersing nanosized oxide inclusions into Nickel - Based alloys. In the new ages of the powder metallurgy field, some workers demonstrated the mechanical alloying induced amorphization (R.L. White for Nb - Sn in 1979, A.E. Yermakov for Co - Y in 1981 and C.C Koch et al. for Ni - Nb in 1983).

During the last 20 years, the mechanical alloying / ball milling process has been successfully used to prepare a variety of alloy powders including powders exhibiting supersaturated solid solutions, quasicrsytals, amorphous phases and nano-intermetallic compounds.

During the mechanical alloying process, the powder particles are periodically trapped between colliding balls and are plastically deformed. Such a feature occurs by the generation of a wide number of dislocations as well as other lattice defects. Furthermore, the ball collisions cause fracturing and cold welding of the elementary particles, forming clean interfaces at the atomic scale. Further milling lead to an increase of the interface number and the sizes of the elementary component areae decrease from millimeter to submicrometer lengthes. At this scale, only the transmission electron microscopy is a suitable way to observe the spatial distribution of the various species. Concurrently to this decrease of the elemetary distribution, some nanocrytalline intermediate phases are produced inside the particles or at the surface of the latters. As the milling duration develops, the volumic fraction of such intermediate compounds increases leading to a stationary end product whose description depends on the milling conditions.

The following Figure will illustrate the various machines which can be used to produce mechanically alloyed compounds.

Figure 2. : Typical milling machines used for mechanical alloying processing

The mechanisms leading to the phase transitions are still in discussion from a fundamental point of view. Nevertheless, some points are no more discussed, i.e. the available mechanical energy which is produced by the various milling machines. Such a mechanical milling energy has been compared to some other solid / liquid state processing leading also to phase transitons under various sollicitations.

Figure 3 : Comparison of the injected power expressed in eV / at.sec as a function of the various solid / liquid state processing leading to phase transitions under various sollicitations.