Effects of minor Si on microstructures and room temperature fracture toughness of niobium solid solution alloys

Controlling the elements content in the niobium solid solution (Nb-ss) is significant for the better comprehensive performance of Nb-suicide-based alloys. In this paper, the effects of minor Si on the microstructures and room temperature fracture toughness of Nb-(0/0.5/1/2)Si-27.63Ti-12.92Cr-2.07A1-1.12Hf (at%, unless stated otherwise) solid solution alloys were investigated. The alloys were processed by vacuum arc-casting (AC), and then heat treated (HT) at 1425 degrees C for 10 h. In HT alloys, Nbss grains are refined gradually with the increase of Si content. Meanwhile, the volume fraction of Cr2Nb and suicides phases precipitates increases. The fracture toughness of HT alloys decreases at first but then increases in the range of 0 to 2% Si, because it is a combinatorial process of positive and negative effects caused by the addition of Si. The refinement of Nb-ss grains displays positive effect on fracture toughness, while the increase of solid solubility of Si in Nbss and brittle Cr2Nb and Nb-suicides precipitate phases display negative effect. (C) 2015 Elsevier B.V. All rights reserved.