Microstructure of Nb／Nb5Si3 in—situ composites

The Nb-10Si(mole fraction,%)alloy was fabricated using the vacuum arc-melting method and heat-treated at 1850℃ and 1550℃ for2-100h in Ar atmosphere.The microstructure of the alloy has been investigated using Xray diffractometry(XRD),scanning electron microscopy(SEM)equipped with X-ray energy dispersive spectrometry (EDS)and transmission electrom microscopy(TEM).The results show that 1550℃,100h is an optimum heat-treatment condition to acquire the equilibruum 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 th alloy is in the metastable equilibrium state.In th case of 1850℃，2h heat-treatment the Nb particles are coarsened evidently.However,in the heat-treatment condition of 1550℃ for 25-100h the growth of Nb particles in unconspicuous.After heattreated at 1550℃，Nd3Si phase transforms into the equilibrium Nb5Si3 and Nb phase with the increase of heat-treatment time gradually.TEM obsevations reveal that the interface of Nb phase Nb5Si3 phase is clean and some twins with about 10nm in width are found.

Microstructure of Nb/Nb5Si3 in-situ composites