Abstract
In this work, a first attempt was made to process TiAl alloys using the Filament Granular Fabrication (FGF) process. The achieved properties are compared to those of material made using a standard Metal Injection Moulding (MIM) process route.
One advantage of the FGF process is that the existing technical infrastructure of the well-established MIM processing route can be used. The FGF process combines this with the advantages of additive manufacturing processes such as high geometrical degree of freedom and optimised material use. Thus, material and machine costs can be reduced. Furthermore, process induced residual stresses and their negative influence on components properties are negligible compared to powder bed-based additive manufacturing processes such as laser or electron beam fusion.
The first step in the process was the production of spherical TNM alloy powder (Ti-43.5Al-4Nb-1Mo-0.1B, in at.%) at Helmholtz-Zentrum Hereon using the Electrode Induction Melting Inert Gas Atomization (EIGA) process. After sieving, the powder fraction < 25 µm was used for the preparation of a feedstock, based on a binder system, consisting of paraffin-wax, ethylene-vinyl-acetate and stearic acid. Thereafter, the feedstock was granulated to 1–3 mm diameter particles and dog bone shaped tensile test specimens were produced, using an AIM3D ExAM 255 printer for FGF processing and an Arburg 370A injection moulding machine for MIM processing. Subsequently, all produced samples were solvent debinded in hexane, thermal debinded and then sintered in an inert argon gas atmosphere. Sintering in the solid/liquid two phase region at a temperature of 1500 °C, led to a sinter density of 99.7%. The resulting microstructures and phases were analysed using SEM and EBSD, as well as high energy X-ray diffraction.
For both the FGF and MIM production techniques, tensile tests were performed at room temperature. In addition, compression creep tests were carried out at two different temperatures, 700 °C and 800 °C, under 150 MPa load.
