Synthesis of nanocomposites and amorphous alloys by mechanical alloying

Mechanical alloying (MA) is a powder metallurgy processing technique that involves repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Due to the specific advantages offered by this technique, MA was used to synthesize a variety of advanced materials. This article presents two specific examples of synthesis of nanocomposites containing a high volume fraction of the reinforcement phase in Al and TiAl matrices. It was possible to uniformly disperse 50 vol% of nanometric (50 nm) Al2O3 in Al and achieve high strength and modulus of elasticity. Similarly, it was possible to disperse 60 vol% of Ti5Si3 phase in the gamma-TiAl intermetallic. Fully consolidated material showed superplastic behavior at 950 degrees C and a strain rate of 4 9 10(-5) s(-1). Amorphous phases were produced by MA of blended elemental powder mixtures in several Fe-based compositions. From the systematic investigations carried out, it was possible to deduce the criteria for glass formation and understand the interesting phenomenon of mechanical crystallization. By conducting some controlled experiments, it was also possible to explain the mechanism of amorphization in these mechanically alloyed powder blends. Other examples of synthesis of advanced materials, e. g., photovoltaic materials and energetic materials, have also been briefly referred to. This article concludes with an indication of the topics that need special attention for further exploitation of these materials.