Effect of gallium addition on the microstructure and micromechanical properties of constituents in NbSi based alloys

The effect of gallium addition on the solidification microstructure and micromechanical properties of constituents was investigated in two sets of Nb16Si(1Ga) (in at.%) and Nb16Si22Ti2Cr2Al2Hf(5Ga) (all in at.%) alloys. The addition of gallium was found to promote the formation of Nb5Si3 and (Nb,Ti)5Si3 phases in Nb16Si1Ga and Nb16Si22Ti2Cr2Al-2Hf5Ga alloys, respectively. Evaluation of micromechanical properties of constituents were done by nanoindentation and micropillar compression testing. Nanoindentation showed that gallium addition reduces hardness and Young's modulus for both Nbss and silicide phases (Nb3Si and (Nb,Ti)5Si3); while it enhances fracture toughness of silicide phases. However, micropillar compressions showed that the addition of gallium decreases the compressive strength of the Nbss phase while increasing the strength of the silicides.