Effect of boron and yttrium on the phase composition and the microstructure of natural Nb-Si composites

The phase formation in Nb-Si composites of a eutectic composition alloyed with 0.2–2.0 at % B and 0.9–6.0 at % Y is considered on model specimens prepared by vacuum arc melting. The phase composition of three-component alloys and the phase transformation temperatures are determined by physicochemical analysis, the specimen density and microhardness have been measured, and the content of alloying elements in the alloys has been determined. It is found that the solidus and liquidus temperatures of the alloyed alloys are almost unchanged within the yttrium and boron concentrations under study, and the difference between the densities of the model specimens and the base Nb-18.7 at % Si is ±1.6%. The introduction of yttrium and boron into the natural Nb-18.7 at % Si composite increases the microstructure dispersion and influences the composition of the strengthening phase: yttrium stabilizes high-temperature silicide Nb3Si at low temperatures, and boron, conversely, catalyzes its decomposition with formation of α-Nb5Si3. © 2014, Pleiades Publishing, Ltd.