Effects of additives on the phase stability of Nb_3Si intermetallic compound and mechanical properties of Nb-Si alloy

摘要

Recently, Nb-Si alloys have attracted attentions as substitutional materials of Ni-based superalloys because of its low density and high melting point. For attaining good room temperature toughness of Nb-Si alloys, proposed is a microstructure-control technique by combining eutectic reaction (L->Nb+Nb_3Si) and eutectoid reaction (Nb_3Si->Nb+ Nb_5Si_3) for spheroidizing Nb_5Si_3 strengthening phase embedded in Nb matrix [1]. For the solid solution strengthening of Nb matrix phase W and Mo are very effective, but Nb_3Si phase disappears by adding these elements of as small as 3 at%. In contrast, Ti and Ta stabilize Nb_3Si phase. For a further alloy development, establishment of an alloy design based on the control of phase stability of Nb_3Si is needed. In the previous study [2], it was revealed that the phase stability of Nb_3Si can be controlled by selecting appropriate Ta/Mo ratio. In the present study, this approach is expanded to other combinations of stabilizing and destabilizing elements of Nb_3Si, such as Ti and W, Ta and W, and Ti and Mo. Vickers hardness tests were conducted on the heat-treated samples to reveal effects of additives on mechanical properties of Nb-Si alloy.