Development of a Novel Heat Treatment Method to Achieve a Fine-grained Near Lamellar Microstructure in Ti-48Al-2Cr-2Nb Intermetallic

The aim of the current research is to achieve a fine grain structure (less than 200 micrometers) in Ti-48Al-2Cr-2Nb Intermetallic by a three-step heat treatment and to investigating the parameters affecting this process. For this purpose, after the homogenization at 1175 C for 24 hours for eliminating the cast structure, three-stage heat treatment including the first stage (single-phase annealing at 1400 C for one hour with cooling in furnace and air environments), the second stage (cyclic operations including repeated heating up to 1400 C for three, five and ten cycles and cooling in air and water environments) and the third stage (Two-phase annealing at temperatures of 1175, 1225 and 1275 C  for one hour) was performed. Finally, single-phase annealing at 1400°C for one hour and cooling in the furnace, then cyclic heat treatment with five cycles at the same temperature with cooling in air and annealing at 1225°C for one hour is suggested as the optimal process to create a semi-lamellar structure with the smallest colony size.