Synthesis of titanium carbide and titanium diboride for metal processing and ceramics production

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 bide is applied to manufacture carbidosteels: 6W5Mo3V ( Р 6 М 5 Ф 3) – 20 % TiC (liquid-phase sintering); 6W5Mo3Co ( Р 6 М 5 К 5) – KT20, 0.6C6Cr3w1Mo1V1Si (6 Х 6 В 3 МФС ) – KT20 (hot isostatic pressing); 6W5Mo5Co ( Р 6 М 5 К 5) – KT20 (hot extrusion); 5W5Mo5Co ( Р 5 М 5 К 5)–20% TiC (hot stamping). Hard- ness of these carbidosteels amounts to 86…90 HRA, resistance to bending reaches 1,300-2,000 MPa [13]. Boron carbide is characterized by a unique combination of low density (2.52 g/cm 3 ), high hardness (up to 40 GPa for hot-pressed items), and chemical inertness combined with a high melting point (2,450 о С ). As a result, ceramics based on boron carbide have found wide application in different areas of the state-of- the-art technology [14]. However, there are some dif fi culties arising for manufacture of B 4 C -based dense ceramics owing to the low value of the self-diffusion coef fi cient (because of the strong covalent bonds between boron and carbon atoms), its low plastic deformation, and high sliding resistance between the com- pound grains [15]. An advanced approach to improving operational characteristics of B 4 C-based ceramics consists in the use of modifying additives. Their presence tends to activate the sintering process by reduc- ing the activation energy, that leads to a decrease in the grain size, an increase in the density, strength, and fracture strength of the sintered compositions. In this case, diborides of transition metals can be used, for example, zirconium diboride [16–19]. Here the objective is to study the synthesis processes of highly dispersed powders of titanium carbide and diboride as advanced materials used in manufacture of cutting tools, wear-resistant coatings, abrasives and ceramics. Research techniques To carry out the synthesis of titanium carbides and diborides , TiO 2 ОСЧ 7-3 ТУ 6-09-3811-79 (the content of the base material – 99 wt.%), nano fi brous carbon – NFC ( speci fi c surface area – 150 m 2 /g, the content of the base material – 99 wt.% [20]), and highly dispersed boron carbide (an average particle size – 2.1 μ m, the content of the base material – 98.5 wt.% [21]) were used as reagents. The experiments on obtaining titanium carbide by carbothermal method were conducted in a resistance furnace fi tted with a graphite heater, but titanium diboride was prepared in a ВЧ –25 АВ crucible-type induction furnace. X-ray studies of the phase composition for titanium carbide and diboride samples were conducted using an ARL X-TRA diffractometer (Thermo Electron SA) with CuK α radiation (wavelength λ = 1.5406 Å). The angu- lar rage (2 θ ) was from 20 о to 70 о . The content of titanium and impurities was determined in the titanium carbide and diboride samples by the X-ray spectral fl uorescence method with the use of an ARL-Advant’x analyzer fi tted with Rh -anode of the X-ray tube. The measurement inaccuracy was 1 %. The total content of carbon in the titanium carbide samples was determined using a LECO S - 144 device. The measurement inac- curacy was 1 %. The content of boron and other elements in the titanium diboride samples was determined by inductively coupled plasma – atomic emission spectrometry ( ICP AES ) using an IRIS Advantage spec- trometer (Thermo Jarrell Ash Corporation). The measurement inaccuracy was 1 %. The surface morphol- ogy and particle sizes of the samples were studied using a Carl Zeiss Sigma scanning electron microscope. The particle/aggregate size distribution was determined with the use of a MicroSizer 201 laser analyzer (BA Instruments). The measurement inaccuracy was < 5%. Results and Discussion The charge for obtaining titanium carbide was prepared by stoichiometry for the reaction: TiO 2 + 3C = TiC +2CO. (1) The experiments on the synthesis of titanium carbide were carried out at the following temperatures, о С : 1,600; 1,800; 2,000; 2,100 (samples 1-1, 1-2, 1-3 and 1-4 respectively). The sample diffractograms are given in Fig. 1. The samples contain not only titanium carbide but also titanium oxide, which was used as a reagent at the temperature of heat treatment – 1,600 and 1,800 о С . At higher temperatures (2,000 and 2,100 о C), the