Starostina A. Formation of nanolayered Mn+1AXn materials in Ti-Al-C(N) systems in a wide range of pressures and temperatures

The dissertation deals with an actual science and technical problem, which consists in the establishing of regularities of the formation of materials with nanolayered Mn+1AXn phases of Ti-Al-C(N) system and their solid solutions over the wide range of pressures (0.5-7.7 GPa) and temperatures (950-1960°C) and basing on which the highly dense Ti3AlC2-based materials with high mechanical and damping characteristics, temperature- and corrosion-resistances in air and hydrogen as well as Ti3AlC2 powders with high polishing ability have been developed. New effective applications of the developed materials were found, namely, structural materials for hydrogen energy needs (particularly for fuel cells), damping substrates for cutting tools and polishing material in finishing jewelry crystals and synthetic stones. It has been established that the increase of nitrogen in Ti2Al(C1-xNx) solid solutions from х = 0 to х = 0.75 leads to a decrease of the material stability against oxidation on heating and an increase of the number of TiC layers in the МАХ phases structures of the Ti-Al-C system causes an increase of the resistance against oxidation in air, which is attributable to an increase of the amount of strong covalent bonds. It has been shown that the resistance to oxidation of the Ti3AlС2-based materials essentially increases as their porosity decreases from 22% to 1%. The damping ability of Ti3AlC2 - based materials was defined and estimated. The logarithmic decrement of oscillation damping, ?, increases as the time and pressure of sintering increase: the increase of sintering time at 0.1 МPа and 1250 оС from 1 to 3 h for the materials with 11-13% porosity ??10 increases from 5.54 ± 0.87 % to 14.16 ± 1.37 %, and in the case of holding time 1 h at 1300-1350 оС the increase of pressure from 0.1 МPа to 30 МPа leads to the increase in 4 times and to the decrease of porosity to 1 %. Synthesized at 5?10-3 МPа and densified according to the developed technology at 30 МPа, 1350°С material that is based on the МАХ phase Ti3AlС2 (89% Ti3AlC2, 6% TiC, 5% Al2O3) demonstrated a unique complex of properties: density 4.27 g/сm3 (porosity 1%); microhardness Нµ = 4.6 GPa (at 5 N), hardness HV = 630 (at 50 N) and HRA = 70 (at 600 N), Young modulus 140±29 GPa; bending strength 500 МPа and compression strength 700 МPа; static fracture toughness 10.2 МPа·m1/2, logarithmic decrement of oscillation damping ??10=24.5 ± 1.8 %. Besides the bending strength even of porous material after holding in hydrogen at 600 оС for 3 h decreased by 5 %, and after holding for 1000 h in air at 600°С the dense material turned out to be more resistant against oxidation than ferrite steels of Crofer GPU and Crofer JDA grades.