Alloying effects on the fracture toughness of Nb-based silicides and Laves phases

Nb-based in situ composites are characterized by a large volume fraction of silicides and Laves phase particles in an Nb solid solution matrix. The intermetallic hard particles can adversely affect the fracture resistance of the composites. Recent work has shown that certain alloy additions can improve the fracture resistance of Nb-based silicides, Laves phases and the Nb solid solution. In this paper, the effects of alloy additions on the fracture toughness of Nb-based silicides and Laves phases are summarized. Theoretical calculations have been performed to determine the influence of alloy additions on the bond order, unstable stacking energy, and the Peierls–Nabarro energy for selected slip systems in the intermetallics. The theoretical results will be used in conjunction with experimental data to elucidate the possible roles of alloy additions in the slip process and the fracture resistance in Nb-based silicides and Laves phases and to compare the observed behaviors against those in Ti-based silicides and Laves phases.