Preparation of Nanocrystalline NiAl Compounds and Composites by Mechanical Alloying

During the past ten years, mechanical alloying/ball milling has been employed to successfully synthesize nanocrystalline NiAl intermetallic compounds (NiAl, NiAl (Cr,Co,Ti,Fe)) and composites (NiAl-TiC, NiAl-TiB2, NiAl-HfC, NiAl-HfB2) in our group, namely, by means of self-sustained reaction. During the mechanical alloying process, an abrupt temperature rise has been observed. The large heat release from the formation of NiAl, as well as HfC, HfB2, TiC, TiB2 compounds is suggested to be the driven force of the self-sustained reaction. It is interested to observe that nanocrystalline NiAl exhibits very well microstructure stability during high temperature annealing. The alloying additions can decrease reaction rate and prolong the reaction time. With the increase of alloying additions, supersaturated solid solution even amorphization of NiAl has been formed. The nanocrystalline NiAl compounds show a rise of the compressive strength and the ductility at room temperature compared with that of the cast coarse crystalline compound.