Preparation of Nb–25Si, Nb–37.5Si, Nb–66.6Si powders by high-energy ball milling and subsequent heat treatment

Abstract

The present paper reports on the syntheses of the Nb 3Si, α-Nb 5Si 3 and NbSi 2 compounds by mechanical alloying and subsequent heat treatment. The milling process was carried out in a planetary Fritsch P-5 ball mill under argon atmosphere using stainless steel balls and vials, rotary speed of 200 rpm and a ball-to-powder weight ratio of 10:1. Following, the milled powders were heat-treated at 1600 °C for 1 h in order to obtain the equilibrium microstructures. The milled and heat-treated powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), microanalysis via energy dispersive spectrometry (EDS). Results indicated that the silicon atoms were dissolved into the Nb lattice during milling to form supersaturated solid solutions. The Nb 3Si compound was formed after heat treatment at 1600 °C for 1 h only, while the Nb 5Si 3 and NbSi 2 compounds were successfully formed during ball milling. Results have indicated that a significant iron contamination close to 5 at% was found in mechanically alloyed Nb–25Si, Nb–37.5Si and Nb–66Si powders. Consequently, the nominal compositions of Nb–Si powders were altered and other phases were also formed after heat treatment at 1600 °C for 1 h.