γ-TiAl materials represent an important class of structural materials which, thanks to their excellent physical and mechanical properties, play an important role in the aerospace and automotive industries. In particular, they are considered an attractive alternative to nickel-based superalloys due to a lower density (about 4 g/cm3 for γ-TiAl alloys and 8 g/cm3 for Ni-based superalloys).
In this work, realized within the European project TIALCHARGER, TiAl-based powders, Ti-48Al-2Cr-2Nb (48-2-2) and Ti-48Al-2Nb-0.7Cr-0.3Si (RNT650), were used to fabricate specimens and prototypes of hollow turbocharger turbines by Electron Beam Melting (EBM). This additive manufacturing technology uses an electron beam to generate parts by selectively melting the powder layer by layer according to CAD data. Components produced with the different powders were characterized in terms of residual defects and resulted appropriate both in terms of overall residual porosity and maximum defect size. Furthermore the microstructure of the as produced material were investigated and heat treatments were set up in order to obtain the desired microstructure. This is an essential point for these materials because their mechanical properties are extremely sensitive to microstructure.
Chemical composition of both 48-2-2 and RNT650 powders and massive materials were analysed. A loss of Al was observed, while the levels of impurities are very low and comparable between the powder and the part.
Furthermore some brazed joints between steel and TiAl processed by EBM were produced. These samples were then tested and characterized in terms of residual defects, micro hardness and microstructure.