Abstract
The effect of heat treatment on the microstructure and hardness of a cast intermetallic Ti-46Al-2W-0.5Si (at.%) alloy was studied. During annealing in the temperature range from 1350 to 1440 °C formation of grains with regular lamellar structure started in the vicinity of the surface and continued towards the central part of the annealing samples. The evolution of the grain size with the annealing time was found to follow a power law with time exponent n ranging from 0.35 to 0.38 and the activation energy for grain growth was determined to be 145 ± 11 kJ mol^-1 in the region of fully or nearly lamellar grains. Lower time exponent of 0.17 was measured in the region of originally equiaxed grains with duplex type of microstructure during annealing at 1415 and 1440 °C up to 5 h. The annealing temperature, time and cooling rate affected Vickers microhardness and hardness. The negligible difference in Vickers hardness values between different regions of the annealed samples was achieved after annealing at 1440 °C for 5 h.

Key words
intermetallics, titanium aluminides, TiAl, heat treatment, microstructure, mechanical properties

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