Formation of NbAl3/Al2O3 composites by pressureless reactive infiltration

Porous preforms of NbO2 with coral-like microstructure were prepared from powder blends of Nb2O5, C, and dextrin [(C6H10O5)(n), where n=10-200] by uniaxial pressing and three-dimensional printing. The compacted powder blends were then pyrolyzed at 800 degrees C for 2 h in nitrogen atmosphere to decompose the dextrin binder into carbon and subsequently presintered at temperatures from 1150 degrees C up to 1400 degrees C for 1 h under Ar atmosphere. Because of interconnected porosity with a mean channel pore diameter of 1.8 mu m for uniaxially pressed preform, and bimodal pore size distribution with pore size maxima of 1 mu m (intraagglomerate pores) and 40 mu m (interagglomerate pores) for printed preform, capillary driven infiltration with Al melt could be achieved at 1200 degrees C without applying external pressure. Subsequent heat treatment at 1400 degrees C for 1 h resulted in the formation of dense NbAl3/Al2O3 composites.