Enhancing strength and ductility of Nb alloy via Y addition by vacuum electromagnetic levitation melting under oxygen carrier route

Abstract

Niobium (Nb) is considered as candidate material for heat pipe in space nuclear reactors due to high melting point, low density, excellent compatibility with alkali liquid metals, irradiation resistance, workability and welding performance, but low strength restricts it's engineering application. In this work, yttrium (Y) was introduced into Nb matrix to achieve solution strengthening from Y atoms and dispersion strengthening from yttrium oxides. The latter one was realized by oxygen carrier route and vacuum electromagnetic levitation melting technique. Finally, one Nb521 (Nb-5.0 wt%W-1.7 wt%Mo-1.0 wt%Zr-0.07 wt%C) and four kinds of Nb521-xY (x = 0.1, 0.2 0.3 and 0.4 wt%) alloys were prepared. TEM characterization indicated that 80 nm Y2O3 particles were formed in Nb521-0.1Y, which exhibited the highest yield strength of 673 MPa, ultimate tensile strength of 740 MPa as well as larger elongation of 12.8%. Moreover, the solution strengthening of Y atoms and Orowan strengthening of yttrium oxides were evaluated quantitatively.

Keywords

• Nb alloy
• Yttrium
• Electromagnetic levitation melting
• Tensile properties
• Strengthening mechanism