Low energy mechanical treatment of non-stoichiometric titanium carbide powder

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 3 2021 50 hours, the CDD size for TiC 0.65 almost does not change, and then with a further increase in the MT time to 100 hours, it decreases. With an increase in the MT time to 20 hours for TiC 0.48 , a sharp decrease in the CDD size from 55 nm to 35 nm is first observed, and with a further increase in the MT time to 100 hours, the CDD size decreases insignificantly. With an increase in theMT time, the values of the CDD sizes for the structural components of the powders TiC 0.65 and TiC 0.48 approach each other, and the extrapolation of the dependences of the CDD sizes shows that after treatment for 115 hours, the CDD sizes for TiC 0.65 and TiC 0.48 will become equal and make about 30 nm. Adifferent behavior of the curves is observed for the dependences of the crystal lattice microdistortions on the MT time for the structural components of the powders TiC 0.65 and TiC 0.48 (Figure 5, b ). It can be seen that within up to 50 hours of exposure, the microdistortions of the crystal lattice of TiC 0.65 and TiC 0.48 are close in values and virtually do not depend on treatment time. A further increase in the MT time to 100 hours increases microdistortions of the TiC 0.65 crystal lattice and decreases microdistortions of the TiC 0.48 crystal lattice. The difference in the dependences of the CDD size and crystal lattice microdistortions on the MT time for the TiC 0.48 and TiC 0.65 phases can be due to a significant effect of the crystal lattice defects: within long treatment time, relaxation of the TiC 0.48 crystal lattice microdistortions can be caused by vacancy ordering phenomena, which occur in more non-stoichiometric TiC x , followed by formation of various superstructures [38, 40]. For an accurate description of the processes occurring in such carbides during mechanical treatment, it is necessary to conduct neutron diffraction studies. The dependences of the ratio of the peak intensities calculated for reflections (111) and (511) of the structural components of the powders TiC 0.65 and TiC 0.48 on the MT time are shown in Figure 6. It can be seen that the ratio of the peak intensities for the (111) reflection does not change up to 50 hours of MT, and then the effect of the impact of MT can be observed; the peak intensity ratio for the (111) reflection increases sharply with an increase in the MT time up to 100 hours. The calculation of the peak intensity ratio for the (511) reflection showed that an increase in the MT time does not cause a change in the peak ratio. The results obtained are in good agreement with the results reported in [25, 32], where similar dependences of the changes in the CDD size and crystal lattice microdistortions were obtained during high-energy treatment. Long time treatment led not only to powder grinding, but also to a strong distortion of the crystal lattice and an increase in the number of defects. Mechanical treatment causes not only the dispersion of particles of titanium carbide powder, but also its activation due to the accumulation of microdamages. Conclusions It was found that with an increase in the time of mechanical treatment of non-stoichiometric titanium carbide powder TiC in a ball mill, the specific surface area of the powder increases from 0.6 to 3.4 m 2 /g, and the average particle size calculated from it decreases from 2 to 0.36 μm. It is shown that the composition of the powder in the initial state corresponds to TiC 0.7 , and after me- chanical treatment, particles of nonstoichiometric titanium carbide consist of two structural components with different atomic ratio of carbon to titanium: TiC 0.65 and TiC 0.48 . Mechanical treatment of the titanium carbide powder leads to a decrease in the microstresses of the TiC x crystal lattice and in the CDD size from 55 to 30 nm for the TiC 0.48 phase. For the TiC 0.65 phase, with an Fig. 6. Ratio of the peak intensities for TiC 0.65 and TiC 0.48 depending on the mechanical treatment time for peaks (111) and (511)