Effect of Cr on Microstructure and Fracture Toughness of Nb-20Ti-16Si-xCr Alloys

The present paper reported the phase stability and microstructures evolution of Nb-20Ti-16Si-xCr (x = 0～20at.%) in-situ composites as function of Cr addition. It was suggested that with the addition of Cr less than 7%, the silicide phase in as-cast Nb-20Ti-16Si alloy was Nb_3Si. The silicides changed to be α-Nb_5Si_3 by the addition of Cr above 7%. It was found that annealing of 1300 ℃ for 100 h could result in the decomposition of Nb_3Si to NbSS and α-Nb_5Si_3 in Cr containing Nb-20Ti-16Si based alloys by means of eutectoid reaction. Whereas in the case of alloy without Cr addition, the Nb_3Si in Nb-20Ti-16Si alloy keep good stability during the high temperature annealing. The Cr additions larger than 5% in Nb-20Ti-16Si-xCr alloys could result in the formation of Cr-rich Laves phase. In addition, the influence of Cr addition on the room temperature fracture toughness of the alloys after annealing was reported.