Microstructure evolution of the Nb-18Si-24Ti-5Cr-5Al-2Mo alloy produced via laser additive manufacturing

Niobium silicide based alloys with composition Nb-18Si-24Ti-5Cr-5Al-2Mo were prepared via laser additive manufacturing and analyzed with back-scattered scanning electron microscope and energy-dispersive X-ray spectroscopy in order to evaluate the solidification sequence during freezing and the microstructure evolution during post heat treatment process. Following primary formation of Nb5Si3, and eutectic reaction L → Nb5Si3 + Nbss, takes place and Nb3Si phase is suppressed, deviating from the equilibrium predictions. Due to high Ti concentration, a second Ti-rich Nb5Si3 phase is formed. After heat treatment at 1200 °C, coarsening of phases has been observed with a decreasing of the Ti-rich Nb5Si3 phase. A new formation of a Tiss solution phase has occurred in small volume fraction, which is related to the local super-saturation and high temperature diffusion. A better understanding of the microstructure evolution was therefore required in order to follow the formation and change of phases from the solidification to the heat treatment stages. This study was focuses on the analysis of the solidification behavior of the multi-component Nb-18Si-24Ti-5Cr-5Al-2Mo alloy under rapid freezing produced via laser additive manufacturing processing posteriorly heat treated at 1200 °C.