Evaluation of the Effect of Heat Treatment on Structural Changes and Mechanical Properties of Ti-48Al-2Cr-2Nb Intermetallic

The purpose of this research is to investigate the effect of different heat treatment cycles on structural changes and mechanical properties of Ti-48Al-2Cr-2Nb intermetallic compound. Heat treatment at 1175°C for 24 hours resulted in the formation of a duplex structure including γ grains along with colonies of γ and α2 layers with an average grain size of 1160 micrometers. Heat treatment at 1400°C for 30 minutes created a near lamellar structure of γ and α2 phases with a grain size of 1300 micrometers. By increasing the time to 60 minutes, a fully lamellar structure with an average grain size of 1120 micrometers was created. The decrease in grain size with increasing the heat treatment time is mostly attributed to the completion of the recrystallization process with the creation of new colonies and the destruction of the remaining gamma grains. Heat treatment at a temperature of 1380C for 45 minutes resulted in the formation of a fully lamellar structure with a grain size of 950 micrometers, but the grain size distribution is more uniform than the lamellar structure formed at a temperature of 1400 degrees. By increasing the volume fraction of colonies, the hardness increased. The hardness of duplex structure was 282 Vickers and the near lamellar structure was 320 Vickers. The results of the stress rupture test showed that the creep rupture life of the lamellar structure was 115 hours, while the life of duplex structure was 22 hours. This difference is attributed to the small distance between the layers.