Abstract:The Nb-10Si (mole fraction, %) alloy was fabricated using the vacuum arc-melting method and heat-treated at 1850℃ and 1550℃ for 2～100h in Ar atmosphere. The microstructure of the alloy has been investigated using X-ray diffract ometry(XRD), scanning electron microscopy (SEM) equipped with X-ray energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). The results show that 1550℃, 100h is an optimum heat-treatment condition to acquire the equilibrium Nb+Nb₅Si₃ two-phase microstructure. The microstructure of Nb-10Si alloy in the as-cast condition consists of continuous Nb₃Si matrix and dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state. In the case of 1850℃, 2h heat-treatment the Nb particles are coarsened evidently. How ever, in the heat-treatment condition of 1550℃ for 25～100h the growth of Nb particles is unconspicuous. After heat-treated at 1550℃, Nb₃Si phase transforms into the equilibrium Nb₅Si₃ and Nb phase with the increase of heat-treatment time gradually. TEM observations reveal that the interface of Nb phase and Nb₅Si₃ phase is clean and some twins with about 10nm in width are found.

Key words: silicides; composites; heat treatment; microstructurev
CLC number:TG146.4