High temperature strength of Nb3Al-base alloys

High temperature strength was investigated as a function of volume percent of Nb₃Al using ternary alloys with controlled microstructures of equiaxed Nb₃Al and Nb_ss (Nb solid solution) grains. Creep strength was examined in Mo-added Nb₃Al-base alloy with two types of different microstructures, equiaxed grains and directionally elongated grains. Mo addition increases high temperature strength at all the volume percents of Nb₃Al, while Ta addition is effective only at high volume percents of Nb₃Al. Ti addition decreases high temperature strength at all the volume percents of Nb₃Al. Mo-added Nb₃Al-base alloy consisting of directionally elongated grains has high creep strength compared to other refractory intermetallic alloys such as MoSi₂ alloy and (Cr,Mo)₃Si/(Cr,Mo)₅Si₃ alloy. Creep strength is decreased under a low applied stress in Mo-added Nb₃Al-base alloy with equiaxed grains probably because of easy grain boundary sliding. The obtained results are discussed in terms of solid solution strengthening of the constituent phases.