Demchenko I. Improvement of strength properties of aluminum matrix composites by carbon nanotubes addition.

The dissertation is devoted to investigation of the effect of carbon nanotubes on the structure formation and mechanical properties of aluminum matrix composites, which were received by casting and powder metallurgy methods. The main difficulty in carbon nanotubes (CNT) addition into aluminum, namely: - the possibility of CNT destruction by dissolution in the matrix as thermodynamic possibility of aluminum carbide formation exists; - the difference of specific density of liquid aluminum matrix and CNT (рAl = 2.4 g/cm3, рCNT = 1.9 g/cm3) that complicates the homogenization of mixtures. The required mass of coating on carbon nanotubes for some metals (W, Mo, Zr, Ni, V, Ti, La, Sc, Hf) was calculated at condition of equality of the densities of carbon nanotubes and aluminum melt. Tungsten coating on CNT was received. It was proved the stable effect of strengthening at CNT (as in with the coating, as without it) addition for three various types of matrices (pure aluminum, cast alloy D16 and recycled aluminum powder) and different conditions of the composites formation. In all cases the sizes of structural components of the matrix decrease, and strength properties of the products increase. Mechanical properties of cast composite D16 (after heat treatment) is very near to deformed alloy properties that will allow us to reduce the deformation ratio or (for some applications) to replace deformed metal by cast one. By addition of CNT into powder sintered composites from recycled aluminum alloy AV87f the sufficient growth of mechanical properties were received. This opens the prospects of inexpensive recycled materials using to production of critical parts of machines. Phenomenon of shape stability (absence of shape changing) of powder samples from secondary AV87f alloy with 1.2% CNT at sintering at the temperature above the liquidus one proves the barrier effect of CNT. This is a reason to increase the temperature range of such composites operation. It is necessary to note that the microstructures of all samples (were manufactured by different methods and with various matrixes) do not content any carbide phases, whose appearance could be caused by CNT destruction.