Microstructure and surface oxides of rapidly solidified Nb-Si based alloy powders

摘要

Spherical pre-alloyed Nb-205i-24Ti-2Cr-2Al powders were prepared by plasma rotating electrode processing (PREP). The microstructure and surface oxides of Nb-Si based alloy powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS) and Auger electron spectroscopy (AES). Results showed that the main phases of Nb-Si based alloy powders were Nbss, beta Nb5Si3 and Nb3Si. Fine lamellar eutectic structure was formed during solidification, taking the central parts of eutectic branches. Anomalous eutectics were distributed at the edges of eutectic branches. The lamellar spacing (lambda) ranged from 0.12 mu m to 0.38 mu m, increasing with the increase of powder diameter. An oxygen-enriched layer with 5.14 nm in thickness, consisting of Nb2O5, SiO2, TiO2, Cr2O3 and Al2O3, was formed on the surface of a powder with 120 mu m in diameter. The amount of oxygen in the oxygen-enriched layer accounted for 49.66% of that in the whole single powder. Formation mechanism of eutectic structures and the surface oxidation mechanism were discussed. (C) 2017 Elsevier Ltd. All rights reserved.