Processing and mechanical properties of mechanically alloyed niobum-rich Nb-Al alloys.

Four Nb-Al alloys containing 15%, 18%, 20% and 25% at. Al were successfully processed by mechanical alloying followed by hot pressing. Analysis of X-ray spectra as well as transmission electron microscopy studies revealed the presence of four phases: niobum solid solution (Nbss), NB3Al, Nb2Al and dispersoids of Al2O3. The grain size was estimated to be = 1 micrometre. The improvement in strength of the mechanically alloyed material was due to the refined grain size and oxide dispersion in the microstructure. The alloys exhibited only limited compressive ductility at room temperature but were ductile at 1000 degrees centigrade. The mechanism for creep deformation in the examined Nb-Al alloys is postulated to be dislocation creep through diffusion controlled climb.