Low energy mechanical treatment of non-stoichiometric titanium carbide powder

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 3 2021 Introduction Materials based on titanium carbide are of great practical and scientific interest today, which is mainly due to a unique combination of its properties. Titanium carbide that possesses such properties as high wear resistance and low friction coefficient, high resistance to aggressive media, high hardness, and resistance to thermomechanical loads, is in demand in various fields for production of protective and wear-resistant coat - ings, heat-resistant ceramics, cutting tools [1–6], and biomaterials in medicine [7, 8]. Porous titanium car- bide is a unique adsorbent to clean the environment from pollutants [9]. In addition, titanium carbide pow- der is also used as a promising material for hydrogen storage [10]. To date, methods of obtaining powders and the study of various properties of titanium carbide have been addressed in numerous studies [11–22]. The main properties are largely studied for stoichiometric or close-to-stoichiometric titanium carbides TiC х . A fundamental distinguishing feature of titanium carbide TiC х is its wide homogeneity region in the carbon concentration range х = 0.33…1.0, i.e. the crystal structure is retained even at carbon vacancy concentration of up to 67 %. Depending on the composition, synthesis conditions, and heat treatment, TiC х carbide can be in a disordered or an ordered state [23]. The properties of TiC in this range of vacancy concentrations can change significantly [23–26], which makes it possible to obtain materials with the required performance characteristics. Practical significance of non-stoichiometric titanium carbides TiC х in engineering, industry, and in medicine is expanding; therefore, it is important to study methods of obtaining non-stoichiometric titanium carbide TiC х and to investigate its properties in a wide range of vacancy concentration. Mechani- cal treatment [27–34], in particular, treatment in a ball mill [34], is one of the most effective ways to influ - ence physical and mechanical properties of powder systems. The energy received by the powder during mechanical treatment, and, accordingly, the activation effects depend on the type of the transmitted action. Mechanical treatment causes such effects as shock, abrasion and crushing, or its combination [25, 27–32, 34]. Ball mill treatment induces a shock-shear effect, when mechanical energy is transferred to the powder system, which results in both grinding of powder particles with the formation of new surfaces and centers of increased activity on these surfaces, and crystal lattice deformation. The process can also involve phase transformations, partial amorphization, formation of various types of defects, etc. However, virtually no systematic studies have been conducted to control, within certain limits, the dispersion, microstructure, stoichiometry of the products after treatment. The purpose of this work is to investigate the effect of low-energy mechanical treatment in a ball mill on the structure, phase composition, and parameters of the fine crystal structure of non-stoichiometric titanium carbide powder obtained by reduction of titanium oxide with carbon and calcium. Materials and research methods TiC powder of composition: Ti – 15 vol. % C obtained by calcium carbide reduction of titanium oxide was the study object. TiC powder was subjected to dry mechanical treatment (MT) in a ball mill with corundum grinding bodies. The mill rotational speed was 40 rpm. The treatment time varied from 5 to 100 hours. The powder structure was studied before and after MT using a Philips SEM 515 scan- ning electron microscope. The specific surface area (SSA) was determined with a SORBI 4.1 device (META, Novosibirsk) by 4-point BET method using low-temperature nitrogen adsorption. The bulk density of the initial powder was determined by the funnel method according to the international stan- dard ISO 3923-1: 2018. The phase composition and parameters of the fine crystal structure of powder materials were investigated by X-ray phase and X-ray structural analyses using a DRON-type X-ray diffractometer (Russia) with filtered CuKα radiation in a 2θ scanning mode from 30 to 145 degrees. The exposure at each point provided a statistical accuracy of not less than 0.5%. The diffraction pro- files were approximated by the Lorentz function. The size of the coherent diffraction domains (CDD) was calculated using the Scherrer equation [35] from the first line of X-ray profiles (111), and the mi - crodistortion of the crystal lattice was calculated using the Stokes-Wilson formula [36] from the last distinguishable line of X-ray profiles (511).