Mechanical Alloying in the Experimental Production of Structural Materials

In the last 10 years we have experimented with the use of the mechanical alloying process to produce a number of materials which could be of interest in structural applications. The materials investigated include intermetallic compounds from the Al-Ni, Al-Ti, Al-Co-Ti and Co-Ti systems, as well as composites of Fe-TiN and Cu-graphite. In most cases, the mechanically alloyed powders have been rapidly consolidated by means of spark plasma sintering. In this way, consolidated products have been obtained which keep the fine microstructure (or nanostructure) conferred by the mechanical alloying process; that is, they constitute bulk nanostructured materials. As a rule, the combination of mechanical alloying and fast sintering has yielded materials with grain sizes typically below 100 nm (nanostructured materials). As a consequence of these refined structures, high mechanical strengths have been observed in most cases in which porosity levels were low. For example, maximum flow stresses as high as 3 GPa were measured in intermetallic alloys of the Al-Ti system having grain sizes below 50 nm. Complications related to contamination during the mechanical alloying process represent a potential problem in most of the experiments performed. Nevertheless, by careful control of process conditions or, perhaps more importantly, clever design of the process and material, this disadvantage can be turned around and even be used to the benefit of the properties of the final product. Such are the cases with the Fe-TiN and Cu-graphite composites investigated in our work.