Thermal expansion of the V5Si3 and T2 phases of the V-Si-B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V5Si3 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 V62.5Si37.5 (V5Si3 phase) and V63Si12B25 (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 V5Si3 phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 x 10(-6) K-1 and 11.7 x 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 x 10(-6) K-1 and 8.3 x 10(-6) K-1 along the, a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti5Si3 phase, the V5Si3 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. (C) 2009 Elsevier Ltd. All rights reserved.