Vibrational dynamics of binary titanium borides is studied from first-principles. Polarized and unpolarized Raman spectra of TiB, TiB₂, and Ti₃B₄ are reported along with the experimental spectra of commercial powder and bulk TiB₂ containing less than 1 wt.% of impurity phases. The X-ray diffraction spectroscopy, applied for phase composition examination of both bulk and powder materials, identifies only the TiB₂ phase. The simulated Raman spectra together with literature data support interpretation and refinement of experimental spectra which reveal components arising from titanium dioxide (TiO₂) and amorphous boron carbide (B₄C) impurity phases as well as graphitic carbon. These contaminations are the by-products of synthesis, consolidation, and sintering aids employed to fabricate powder and bulk titanium diboride.

Density functional theory studies on the Ti ₅ Si ₃ C _x systems with various concentrations of carbon impurities ( ) are reported. The effects of interstitial carbon atoms on crystal and electronic structures, and on the elastic and vibrational properties of the Ti ₅ Si ₃ C _x compound are analysed and discussed. The results of the present investigations indicate not only strong bonding between carbon atoms and their neighbouring titanium atoms, but also the effects of carbon impurities on the atomic bonds beyond the immediate proximity of the dopants. These determine to a great extent the electron densities of states, and the structural and elastic properties of the Ti ₅ Si ₃ C _x Nowotny phases. Although carbon atoms tend to stabilise Ti ₅ Si ₃ C _x phases, they also have a negative effect on their ductile properties. The strong impact of carbon impurities on the lattice dynamics of Ti ₅ Si ₃ C _x compounds is revealed by the phonon and Raman spectra, which remain sensitive to changes in the interatomic distances. In C-doped systems the phonon bands originating from the vibrations of carbon impurities appear at high frequencies and remain well-separated from the lower lying phonon bands dominated by the vibrations of Ti and Si sublattices. The lower frequency phonon bands also experience changes due to the incorporated dopants. Impurities occupying the interstitials of the Ti ₅ Si ₃ lattice are responsible for the appearance of new infrared active and optically inactive modes of A _{2 u} , E _{1 u} and E _{2 u} symmetries, leaving the number of Raman active modes unchanged. Modifications to the dynamical properties of ternary Ti ₅ Si ₃ C _x phases manifest themselves via shifts and the suppression of phonon peaks as well as the emergence of new phonon peaks which are absent in the binary Ti ₅ Si ₃ system. The observed effects become enhanced with an increased concentration of carbon impurities.

The paper presents the influence of the temperature of the sintering process on the microstructure and selected properties of boron carbide/TiB₂/SiC composites obtained in situ by spark plasma sintering (SPS). The homogeneous mixture of boron carbide and 5% vol. Ti₅Si₃ micropowders were used as the initial material. Spark plasma sintering was conducted at 1700 °C, 1800 °C, and 1900 °C for 10 min after the initial pressing at 35 MPa. The heating and cooling rate was 200 °C/min. The obtained boron carbide composites were subjected to density measurement, an analysis of the chemical and phase composition, microstructure examination, and dry friction-wear tests in ball-on-disc geometry using WC as a counterpart material. The phase compositions of the produced composites differed from the composition of the initial powder mixture. Instead of titanium silicide, two new phases appeared: TiB₂ and SiC. The complete disappearance of Ti₅Si₃ was accompanied by a decrease in the boron carbide content of the stoichiometry formula B₁₃C₂ and an increase in the content of TiB₂, while the SiC content was almost constant. The relative density of the obtained boron carbide composites, as well as their hardness and resistance to wear, increased with the sintering temperature and TiB₂ content. Unfortunately, the reactions occurring during sintering did not allow us to obtain composites with high density and hardness. The relative density was 76–85.2% of the theoretical one, while the Vickers hardness was in the range of 4–12 GPa. The mechanism wear of boron carbide composites tested in friction contact with WC was abrasive. The volumetric wear rate (Wv) of composites decreased with increasing sintering temperature and TiB₂ content. The average value of coefficient of friction (CoF) was in the range of 0.54–0.61, i.e., it did not differ significantly from the value for B₄C sinters.

The microstructure, mechanical properties, and friction-wear performance of (TiB_x/TiSi_yC_z)x3 multilayer coatings deposited on the M2 steel by the pulsed laser deposition are investigated in detail in as-deposited state and after annealing at 500 °C for 5 min in air. Scanning and transmission electron microscopies are used to reveal microstructural changes caused by annealing. The influence of post-deposition annealing on hardness and Young modulus is studied in nanoindentation test. A scratch-test is applied to reveal changes in adhesion and the coefficient of friction (CoF) of coated samples with diamond before and after annealing. Friction-wear properties are also analyzed in dry sliding with Al₂O₃ and 100Cr6 steel in ball-on-disc tests. Our analysis shows that the post-deposition annealing leads to partial devitrification of the TiB_x layers, where nanocrystalline TiB₂ phase is identified, while the TiSi_yC_z layers retain amorphous. Annealing significantly increases mechanical properties of coated samples and adhesion of the (TiB_x/TiSi_yC_z)x3 multilayer to steel substrates. Friction-wear properties of coated samples are also notably improved. The values of CoF for coated samples tested with diamond (in the scratch-test), alumina, and 100Cr6 steel (ball-on-disc tests) are in the range of 0.05–0.23, while for M2 steel the CoF values are 0.8, 0.45, and 0.8, respectively.