Microstructure and fracture toughness of powder-processed Al₃Nb

Intermetallic alloys with the nominal compositions Al–24.5Nb, Al–25Nb, and Al–25.5Nb (at.%) were fabricated by hot-pressing of pre-alloyed powders in graphite dies in vacuum. The hot-pressed disks contained substantial porosity even at processing temperatures of 0.95 T_m, where T_m is the absolute melting point. In addition to some copper and silicon contamination, significant concentrations of oxygen and carbon were measured in Al–25.5Nb. Alpha alumina precipitates as well as niobium-enriched precipitates were identified. The fracture toughness of pre-cracked bend specimens with the nominal composition Al–25.5Nb was found to be 2.5 ± 0.5 MPa m^1/2. Possibilities for improving this value are discussed.