Nikolai A. Popov

This study investigates the fabrication of TiC-SiC-TiB₂-reinforced aluminum matrix composites via laser melting, examining the synergistic effects of powder pre-treatment and laser processing parameters on microstructural evolution and mechanical properties. Mechanical alloying of precursor powders for 120 min optimized ceramic particle refinement and reinforcement homogeneity, enhancing density and hardness while providing an ideal substrate for subsequent laser processing. Laser melting experiments conducted at 610 W, utilizing substrate temperatures of both ambient (room temperature) and 400 °C, revealed that pre-heating to 400 °C extended melt duration and enhanced microstructural uniformity. This resulted in coarser primary silicon particles (~10 μm), contrasting with the inhomogeneous structure formed at room temperature, which contained finer silicon particles (~3 μm). Higher laser power mitigated TiB₂ segregation, enabling reactive participation in TiC/Si formation and diffusion-driven spheroidization. Apparently, decomposition of SiC released silicon into the matrix and carbon for the in-situ formation of TiC, MAX phases (Ti₃SiC₂), and Al₃Ti. Microhardness increased with laser power, peaking at 380 HV_0.1 after laser melting at 370 W.

—The effect of the initial structures of titanium alloys containing 10 wt % aluminum and additionally alloyed with molybdenum, niobium, zirconium, and/or tin, which are formed by quenching from various phase regions, on the structure formation in the course of prolonged isothermal annealing at 650°С is studied. It is shown that, in alloys quenched from temperatures corresponding to the β region to form the α' martensite, the decomposition of the martensite and formation of the α-, α₂-, and β-phases mixture within initial martensite plates occur. In this case, the formation of the α₂ phase is realized via the nucleation and growth mechanism. In the alloys quenched from temperatures corresponding to the two-phase region, the spinodal decomposition occurs within the primary α-phase crystallites, and the α + α₂ structure characterized by a great amount of antiphase boundaries forms.

The effects of additional alloying of titanium alloys containing 10 wt % aluminum with molybdenum, niobium, zirconium, and tin on the structure formation of upon quenching from the temperatures corresponding to the single-phase (β) and two-phase (α + β) regions, and on the crystal lattice parameters of the phases that are present in the quenched state are studied. It is shown that α'-martensite with a packet morphology is formed after quenching from the β-region. Alloying with zirconium increases the dispersity of the structure. In alloys quenched from the two-phase region, an α + α'-structure with a small amount of the α₂‑phase is formed. The effect of alloying on the lattice parameters of the α- and α'-phases is analyzed.

Phase transitions in the Co-rich part of the Co–Al–Nb–Mo phase diagram are studied by energy dispersive spectroscopy (EDS), X-ray analysis, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) measurements. The obtained results were compared with the results for alloys of the binary Co–Al and ternary Co–Al–Nb, and Co–Al–Mo systems. Formation of the intermetallic phase with the L1₂ structure was found in a range of alloys with 10 at.% Al, 2–9 at.% Nb, and 3–7 at.% Mo. Intermetallic compound Co₂Nb, Laves phase with the different chemical composition and crystal structure (C14 and C36) was detected in the Co–Al–Nb and Co–Al–Nb–Mo samples after vacuum solution treating at 1250 °C for 30 h.

Specific features of the microstructure formation of an Al–2.5% Fe–1.5% Mn alloy owing to the cooling rate during casting and during laser melt