On the Sub-Structural Phase Transitions in $\alpha$-Titanium Containing Interstitial Microimpurities

Issues » Volume 42, Issue 6

V. I. Savenko$^{1}$, L. I. Kuksenova$^{1,2}$, R. R. Khasbiullin$^{1}$, A. A. Shiryaev$^{1}$

$^{1}$Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31, Bld. 4, Leninsky Ave., 119071 Moscow, Russia
$^{2}$Mechanical Engineering Research Institute RAS, 4, Malyy Kharitonyevskiy Pereulok, 101990 Moscow, Russia

Received: 02.09.2019; final version - 02.02.2020. Download: PDF

The methods of differential scanning calorimetry (DSC), differential thermogravimetry (DTG), mass spectrometry and X-ray diffraction analysis are used to study substructural phase transitions, which are possible at elevated temperatures in powdered $\alpha$-titanium containing nonmetallic microimpurities. The presence of two mutually displaced on the temperature scale due to hysteresis of endo- and exoenergic peaks, which have complex structure and correspond to phase transitions of the 1$^{\textrm{st}}$ kind in the system, is found. Analysis of the results of DTG experiments shows the complete absence of any heterophase reactions in the material, including the processes of its oxidation and thermal degradation during thermal cycling. Mass spectrometric analysis also does not detect desorption of atoms or molecules of hydrogen, carbon, nitrogen, oxygen, water and carbon dioxide from the material in the temperature range of localization of DSC-endothermic peak $\Delta T$ = 300–400°C. Thus, it can be assumed that the observed energy peaks are due to substructural phase transitions in the material of powder particles during their heating and cooling. The microstructural and energy characteristics of these transitions are determined. As shown, the material of powder particles contains two types of microphases. One of them is a microphase consisting of colloidal-sized formations that are coherently included in the hexagonal close-packed (h.c.p.) lattice of titanium and contain interstitial atoms in the form of a solid solution in its $\alpha$-phase. Another type of microphases are foreign inclusions of the composition Ti$_x$A$_y$ and Ti$_x$B$_y$C$_z$, also containing atoms of {A; B; C} = {H; C; N; O} and having a crystal lattice different from the h.c.p. lattice of $\alpha$-titanium. In microphases of both types, due to the deviations of the composition of these microphases from the stoichiometric one, structural phase transitions of the order–disorder type can occur. Within the framework of the mean field approximation, the estimation of changes in the order parameters in these phases at the corresponding phase transitions is obtained. The energy characteristics of the interaction of embedded atoms with each other, defined in the same approximation, are close to their values known from the literature.

Key words: titanium, non-stoichiometric phases of interstitial atoms, substructural phase transitions, differential scanning calorimetry, X-ray diffraction analysis.

URL: http://mfint.imp.kiev.ua/en/abstract/v42/i06/0853.html

DOI: https://doi.org/10.15407/mfint.42.06.0853

PACS: 61.05.cp, 61.43.Gt, 61.50.Ks, 61.72.S-, 64.60.Cn, 64.75.Nx

Citation: V. I. Savenko, L. I. Kuksenova, R. R. Khasbiullin, and A. A. Shiryaev, On the Sub-Structural Phase Transitions in $\alpha$-Titanium Containing Interstitial Microimpurities, Metallofiz. Noveishie Tekhnol., 42, No. 6: 853—868 (2020) (in Russian)

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