Materials Synthesis by Mechanical Alloying

Novel processing methods have received much attention in recent years. This interest is driven by the need to develop new and improved materials to lift material limitations on many applications. Nonequilibrium pro­ cessing methods that result in metastable structures can often synthesize materials with unique properties. Enormous effort has been devoted to one of these techniques, namely, rapid solidification. Rapid solidification methods can modify materials by refining the microstructure, homo­ genizing the composition, extending solid solubilities, creating metastable crystalline phases, or producing metallic glasses. Parallel material modi­ fications can be achieved with the relatively less-studied technique of mechanical alloying (MA). The thesis of this review is that mechanical alloying is a nonequilibrium processing technique analogous to rapid solidification with specific advantages and disadvantages. Mechanical alloying was first developed by Benjamin and coworkers at the International Nickel Company in the late 1960s (1). The goal of this effort was the production of complex oxide dispersion-strengthened (ODS) alloys. The commercial applications of MA have centered on the devel­ opment of ODS Ni-base superalloys, Fe-base ODS alloys, ODS aluminum alloys, and coatings for high temperature alloys. Several reviews of MA have appeared in recent years in which the development of the ODS alloys has been covered (2, 3, 4, 5). This subject will therefore not be considered in detail in the review. The synthesis of amorphous alloys by MA has been reviewed recently by Weeber and Bakker (6). However, since this is a relatively recent area of research and not as well-known as the ODS work, a summary of the main results will be included in the review.