The influence of Field‐Assisted Sintering Technology (FAST) temperature and cooling rate on the microstructural evolution in gamma‐titanium aluminide alloy GE4822

Field-Assisted Sintering Technology (FAST) has potential as a pre-processing step for forging γ-titanium aluminides, but its influence on the microstructural evolution of these intermetallics remains incompletely understood. This study investigates the effect of FAST dwell temperature and subsequent cooling rate on γ-lamellar colony size and volume fraction in γ-titanium aluminide alloy GE4822. Dwell temperatures were set between 1300 and 1400 °C, followed by controlled cooling at 0.1, 0.5, 1, 2 or 3 °C/s, with a free-cooling condition applied at each temperature. The γ-lamellar colony size and volume fraction were measured after dwell and cooling. At dwell temperatures below 1350 °C, γ-lamellar volume fractions remained low, regardless of cooling rate. Conversely, dwell temperatures of 1375 °C or higher produced consistently high volume fractions, with colony size increasing at slower cooling rates. The greatest microstructural sensitivity occurred at 1350 °C, where increasing the cooling rate from 1 to 2 °C/s reduced the γ-lamellar fraction from ∼80% to ∼10% and colony size from 200 μm to less than 50 μm. Substantial γ-lamellae colony volume fractions only formed when cooled through the α-transus, approximated at 1335 °C.