Modification of the microstructural features and hardness of γ-TiAl by heat treatments

γ-TiAl intermetallic alloys are very attractive materials for aerospace applications because of their excellent specific properties at high temperatures. Particularly, γ-TiAl alloys will replace the heavier Ni-based superalloys currently used for low pressure turbine (LPT) blades manufacturing. The main objective of this research work is to study the microstructural evolution during heat treatments in a Ti-45Al-2Nb-2Mn (at.%) + 0.8 (vol.%) TiB2 alloy (Ti4522XD). The alloy was initially processed through hot isostatic pressing (HIP) of prealloyed powder and centrifugal casting (CC). In order to generate a wide variety of microstructures, heat treatments were carried out at defined temperatures accordingly to the γ-TiAl phase diagram. Microstructural characterization was achieved by scanning electron microscopy (SEM) and atomic force microscopy (AFM). For the obtained micrographs, the colony and grain size were measured together with the volume fraction of the different phases and a first approach to lamellar spacing was performed. Furthermore, microhardness Vicker tests were carried out with the aim of analysing the resulting mechanical properties. For these results, conclusions concerning the microstructure evolution of this alloy during heat treatments are drawn. It is proved that the γ-TiAl microstructure is highly sensitive to the heat treatments temperature. Highest hardness values are associated to microstructures composed by a balanced proportion of lamellar colonies and equiaxed grains. This is a first approach to establish a relationship between the microstructure and different heat treatments that can be complemented with defined further research.Ingeniería Aeroespacia