Microstructure of Nb/Nb5Si3 in-situ composites
(Beijing Institute of Aeronautical Materials, Beijing 100095, China)
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
CLC number:TG146.4