TiAl alloy is regarded as a one of the strongest candidates for high temperature materials due to the superior properties, especially creep property, at high temperature. Creep resistance is known to be changed remarkably with lamellar spacing. Although the creep resistance seems to be improved by control of lamellar spacing, the study about controlling lamellar spacing has been limited. For the reason, the creep characteristics with lamellar spacing is investigated.
The microstructure in TiAl alloy strongly depends on the heat treatment. The method to change only lamellar spacing is obtained by controlling the holding time(0.5hr and 2hr) near the α transus temperature(1380℃) and cooling rate(furnace cooling, air cooling). So, the lamellar spacing is 0.4㎛ in fine lamellar, 1.4㎛ in coarse lamellar. From the result of creep, It is found that fine lamellar has better creep resistance than coarse lamellar.
As the creep strain increased within the primary regime, the activation for creep increases to the activation energy for diffusion and the dislocation density increases in general metal. However, EPM TiAl ally shows different behavior. : In case of fine lamellar, the dislocation density significantly decreases and the activation energy is changed from 300kJ/mol, the activation energy for diffusion, to 389kJ/mol. In case of the coarse lamellar, the dislocation density is not changed significantly in part of large lamellar spacing, but that of small lamellar spacing follows the trend of fine lamellar. The activation energy for creep in coarse lamellar changed from 300kJ/mol to 364kJ/mol which is smaller than fine lamellar.
From the above result, it can be known that the rate controlling process for creep is the generation of dislocation by $α_2$ phase transformation in fine lamellar but balances between the generation of dislocation by $α_2$ phase transformation and dislocation climb in case of coarse lamellar.
