27th IFHTSE CONGRESS & EUROPEAN CONFERENCE ON HEAT TREATMENT 2022

Additive manufacturing (AM) processes enable to produce complex three-dimensional parts directly from CAD models. Due to layer by layer formation, as-built materials typically show finer solidification microstructures and mechanical properties compared to the same parts produced by conventional routes. Well established that the elimination of any post treatment remains a big challenge of AM, in most cases a suitable heat treatment is necessary to recover the as-built microstructure produced by the rapid solidification, to optimize the final properties and releasing the internal stresses generated by the 3D process.
In the present work the influence of heat treatments on the properties of some selected tool steels and Ti alloys alloy are considered. Both, Laser powder bed fusion (LPBF) and Direct Energy Deposition (DED) of tool steel leads to the formation of a martensitic structure, showing a very high mechanical strength, but a very limited fracture elongation. The microstructure and properties like hardness, fracture toughness and thermal fatigue resistance can be tuned by conventional quenching and tempering but, in some cases, also by direct tempering. The results obtained by the author in heat treating of AM tool steels will be reviewed.
Laser powder bed fusion (LPBF) of Ti6Al4V leads to the formation of a martensitic structure, showing a very high mechanical strength, but a very limited fracture elongation (5%). In view of the high reactivity to Oxygen of Ti alloys, vacuum treatments (<10-5bar) must be carried out to minimize the detrimental influence of the alpha case. Different annealing treatments affect the microstructure as well as mechanical strength and ductility. All the treatments investigated cause a drop of strength and an increase of fracture elongation, which become larger and larger by increasing temperature. The influence of heat treatment on the properties of a beta-Ti21S alloy will be also reported.