MECHANICAL ALLOYING OF Al-C SYSTEM

摘要

A method of mechanical alloying process is described. Carbon transformation to Al_4C_3 is characterised within the different heat treatment schedules and nine commercial carbon powders are tested. The micromechanism of carbon incorporation into the metallic powder, and its compacting are described. The influence of dispersed carbides on mechanical properties is evaluated together with the influence of deformation on microstructure and properties.It was proved that the transformation efficiency of carbon to Al_4C_3 by heat treatment of aluminium with the porous furnace black and electrographite is higher than that of the hard cracked graphite. Microstructure changes consisted of fracture processes and welding of the particles with incorporation of C phase and forming of final granules. The dispersed phase Al_4C_3 particle size was measured on 200 to 300 thin foil structures, and it was constant and as small as 30 nm. The particle size was influenced neither by the carbon type nor by the heat treatment applied. Subgrain size measured in the range of 100 grains in thin foils depended on the carbon type, as well. It ranged from 0.3 to 0.7 μm. Using a depth sensing indentation (DSI) technique, the Martens hardness, indentation modulus E and deformation work W for Al matrix and Al_4C_3 particles have been measured. It has been shown that the hardness of particles is 5-7 times higher than the hardness of the matrix. The temperature dependence of ductility, and reduction of area in the temperature range of 350 -450°C and strain rate of 10~(-1) s~(-1), indicated a considerable increase of these properties. In a case when the volume fraction of Al_4C_3 changes from lower to higher, the grain rotation mechanism dominates instead of the grain boundary sliding.