Thermal expansion of the Ti 5Si 3 and Ti 6Si 2B phases investigated by high-temperature X-ray diffraction

Abstract

The thermal expansion coefficients (CTE) of the Ti 5Si 3 and Ti 6Si 2B phases were determined using high-temperature X-ray diffraction from 298 to 873 K. Alloys with nominal compositions Ti 66Si 34, Ti 62.5Si 37.5, Ti 59Si 41 and Ti 66.7Si 22.2B 11.1 (at%) were prepared through arc-melting followed by heat-treatment at 1473 K during 60 h under argon atmosphere. The Ti 5Si 3 phase has a hexagonal structure, space group P6 3/mcm (No. 193) with room temperature lattice parameters a=7.4561 Å and c=5.1485 Å. This binary compound presents high thermal expansion anisotropy ( α c/ α a≅2.7), as a consequence of the large difference between the thermal expansion coefficients along the a (5.98×10 −6 K −1) and c (16.64×10 −6 K −1) axes. The Ti 6Si 2B phase crystallizes with a hexagonal unit cell, space group P 6 ¯ 2 m (No. 189) with room temperature lattice parameters a=6.8026 Å and c=3.3374 Å. This phase exhibits a low thermal expansion anisotropy ( α c/ α a≅1), with the thermal expansion coefficients along the a and c axes equal to 9.7×10 −6 K −1 and 9.6×10 −6 K −1, respectively.