Microstructure, mechanical properties and oxidation behavior of powder compacts of the Nb–Si–B system prepared by spark plasma sintering

Abstract

Powder compacts with eight different compositions in the Nb–Si–B system were prepared by spark plasma sintering and their microstructure, mechanical properties and oxidation behavior were investigated. Oxidation resistance of Nb5Si3B2 compacts is better than that of Nb5Si3 compacts, but extremely poorer than that of NbSi2 compacts. However, since the oxidation experiment was of short duration, details of the oxidation behavior of Nb–Si–B compacts have yet to be investigated. Compacts were prepared via the following three different routes: (i) elemental powders were mixed in a rotational ball mill and then consolidated by spark plasma sintering method, (ii) elemental powders were mechanically alloyed and consolidated similarly to (i) and (iii) pulverizing compacts prepared via route (i) and consolidated once again similarly to (i). Compacts prepared via the third route exhibit more homogeneous microstructures and contain a smaller amount of SiO2 than compacts prepared via the other two routes. Compacts with compositions around the line of Nb5Si3–Nb5Si3B2–NbB2 exhibit a high hardness at room temperature and a high compressive strength at high temperatures in comparison to those with compositions away from the line. The strength of compacts containing NbSi2 decreases with increasing the volume fraction of NbSi2 phase.