γ-TiAl alloys produced by Electron Beam Melting for aerospace and automotive applications

Concept 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 [1]. In this work, realized within the European projects TIALCHARGER and E-BREAK and the Regional Project Great2020 FaseII, three kind of γ-TiAl alloys have been investigated: 48-2-2 alloy (aerospace, E-BREAK), TNM alloy (aerospace, E-Break, Great2020 FaseII) and RNT650 alloy (automotive, TIALCHARGER) [2]. Motivations and Objectives The Electron Beam Melting.(EBM) is an additive manufacturing technology that uses an electron beam to generate parts by selectively melting the powder layer by layer according to CAD data. This technology presents several advantages in terms of costs and energy saving compared to the conventional manufacturing processes. The aims of this work are the evaluation of the powder’s recyclability and the optimization of the EBM process parameters using a DOE to obtain the desired microstructure for a specific application after the heat treatment on the well known 48-2-2 alloy, and contemporary the set up of EBM process and the heat treatments on new generation alloys: TNM for turbine blades and RNT650 alloy for turbocharger wheels. Results and Discussion Regarding the recyclability, the analysis performed on powder recycled several times and used for several EBM cycles confirm that, for what concerns particle size distribution, flowability and apparent density, the recycling process adopted doesn’t change the powder properties. Regarding the chemistry, is evident that the recycling process generate only a very small amount of oxygen pick-up which will not affect the specimen production. For the TNM alloy, two heat treatment that gives a near lamellar microstructure with the presence of some β-phase have been set. This kind of microstructure is considered the most promising, for the application of this alloy, in terms of tensile properties with sufficient creep properties. For the RNT650 alloy an heat treatment was set up to obtain a near lamellar microstructure both on samples bars that on hollow and full turbocharger wheels.