Thermal expansion of the V 5Si 3 and T 2 phases of the V–Si–B system investigated by high-temperature X-ray diffraction

Abstract

The thermal expansion anisotropy of the V 5Si 3 and T 2-phase of the V–Si–B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V 62.5Si 37.5 (V 5Si 3 phase) and V 63Si 12B 25 (T 2-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V 5Si 3 phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 × 10 −6 K −1 and 11.7 × 10 −6 K −1, respectively. Similarly, the thermal expansion anisotropy value of the T 2-phase is 0.9 with thermal expansion coefficients equal to 8.8 × 10 −6 K −1 and 8.3 × 10 −6 K −1, along the a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti 5Si 3 phase, the V 5Si 3 phase presents lower thermal expansion anisotropy. The T 2-phase present in the V–Si–B system exhibits low thermal expansion anisotropy, as the T 2-phase of the Mo–Si–B, Nb–Si–B and W–Si–B systems.