Effects of Zr on the Eutectoid Decomposition Behavior of Nbsub 3Si into (Nb)/Nbsub 5Sisub 3

The effect of Zr on the formation of Nb/Nbsub 5Sisub 3 lamellar microstructure by eutectoid decomposition reaction of Nbsub 3Si is investigated. It has been shown that the kinetics of the eutectoid decomposition of high-temperature Nbsub 3Si phase into Nb and Nbsub 5Sisub 3 phases are sluggish in the binary Nb-Si system and that they are enhanced by Zr additions. The time-temperature-transformation (TTT) diagram for the decomposition is experimentally determined and the acceleration of the reaction by small Zr addition of 1.5 at. pet is confirmed by comparison with the reported TTT curves of binary and ternary alloys containing Ti. The role of the ternary element on the decomposition kinetics is discussed in terms of crystallographic orientation relationships (ORs) and Zr distribution in the parent Nbsub 3Si phase during solidification. [PUBLICATION ABSTRACT]