Thermal expansion of the nanocrystalline titanium diboride

Abstract

The research of thermal expansion of nano- and microcrystalline TiB2 in the temperature range of 298–1473 K was carried out by the high-temperature X-ray diffraction method. The grain size effect on the temperature dependence of a and c parameters of TiB2 hexagonal unit cell was established. For nanocrystalline TiB2 with the 5–7 nm coherent scattering region, we found the linear dependence of the metric of the cell on temperature. The thermal expansion coefficient (TEC) of nanocrystalline TiB2 does not depend on temperature and equals 3.58‧10−6 K−1 and 9.92‧10−6 K−1 for the a and c axis respectively. For the microcrystalline TiB2, we detected the nonlinear temperature dependence of unit cell parameter a, which points to the effect of temperature on the coefficient of thermal expansion along a basal plane. The TECa rises from 6.02·10−6 to 9.94·10−6 К−1 in the range of 300–1473 K, while the TECc weakly depends on temperature and remains constant ∼8.38·10−6 К−1, leading to isotropic thermal expansion of microcrystalline TiB2 at 1273–1473 K. The equations which describe the changes of unit cell parameters and coefficients of thermal expansion of nano- and microcrystalline TiB2 as temperature functions are determined.