MECHANICAL ALLOYING OF AL-20 MASS-PERCENT-TI MIXED POWDERS

Alloying processes, formation of amorphous phase and hardening of Al-20 mass % (12.4 at %) Ti mixed powders during mechanical alloying with an Attritor type of ball mill, have been investigated by means of optical, scanning and transmission electron microscopy, X ray analysis and hardness measurements. The mechanical alloying (MA) process detected consists of flake-forming, cold welding of the flaked powders, fracturing of the composite powders, formation of solid solution and amorphous phase. The amount of solute titanium in the composite powder after 493.2 ks MA was estimated to be about 17 mass % from the lattice parameter measurement and grain sizes of the matrix aluminum were in the range from about 20 to 60 nm. The amount of oxygen in mechanically alloyed powders increased with milling time, and dispersions of Al2O3 particles were observed by TEM. The spherorized composite powders with the average particle size of 0.6 μm after 2200 ks MA were amorphous. The amorphous particles showed halo patterns in electron diffraction and showed no grain boundary, no dislocation and few Al2O3 particles in TEM. A remarkable increase in hardness of the composite powders was explained in terms of solid solution hardening of titanium in aluminum, dispersion hardening of Al2O3 particles, work-hardening and hardening by grain refinement.