Lattice parameters and thermal expansion of the T2-phase of the Nb–Si–B system investigated by high-temperature X-ray diffraction

The lattice parameters and thermal expansion coefficients (αa and αc) of the T2-phase of the Nb–Si–B system with different boron contents were determined from high temperature X-ray diffraction data (298–1473 K). Alloys with nominal compositions Nb62.5Si37.5, Nb64Si30B6 and Nb64Si14.4B21.6 (at.%) were prepared from high-purity materials through arc melting and heat-treatment under vacuum. Both a and c lattice parameters decrease with increasing boron content. A significant decrease in αc is observed with increasing boron content while αa remains practically unchanged, diminishing the anisotropy ratio αc/αa from approximately 1.2 at the binary composition to approximately 0.7 at Nb64Si14.4B21.6.