Low energy mechanical treatment of non-stoichiometric titanium carbide powder

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 3 2021 Results and discussion Figure 1, a shows a SEM image of the initial TiC powder. The initial TiC powder is weakly agglom- erated and consists mainly of irregular shaped particles. Along with the fragmented and spongy particles characteristic of powders obtained by the reduction method, the powder contains particles with a shape close to spherical. Powders show a wide unimodal particle size distribution; along with small (up to 2 µm) particles, the powder contains large, agglomerated particles up to 25 µm in size (Figure 1, b ). Fig. 1. SEM image ( a ) and particle size distribution ( b ) of the initial TiC powder a b The average particle size, including agglomerates, calculated by the method reported in [37] is 6 μm, and the average crystallite size determined from the X-ray reflection broadening is 55 nm. The SSA of the initial powder was 0.6 m 2 /g, and the bulk density was 0.1 ρ theor . The SSA of the titanium carbide powder versus the MT time is shown in Figure 2. It can be seen that the SSA of the initial powder was low, and low-energy treatment caused its noticeable changes. With an increase in the mechanical treatment, the SSA significantly increased. The most intensive increase in the SSA (more than 5 fold), occurred during MT within up to 50 hours, and with further increase in the MT time up to 100 hours, the dependence saturated and the SSA was 3.4 m 2 /g. The calculation of the powder particle size from the SSA values under assumption of particle sphe- ricity showed that its size decreases from 2 μm to 360 nm at increased MT time (Figure 2). The particle size of the TiC x powder during treatment can be influenced by both grinding parameters and changes in its stoichiometry. In particular, in [25, 32, 34], it is shown that an increase in the time of grinding of TiC x powder leads to a decrease in the particle size, and under similar grinding conditions, the size of the particles of the crushed powder depends on the relative content of nonmetals x, i.e. on the stoichi- ometry of TiC x carbide [23]. The change in the titanium carbide stoichiometry during MT can be seen based on the analysis of the X-ray diffraction patterns before and Fig. 2. Change in the specific surface area (SSA) and the TiC powder particle size calculated from these values vs. the mechanical treatment time