Laser Additive Manufacturing for the Realization of New Material Concepts

In additive manufacturing processes, components are built up in layers from liquids, powders, wires or foils using chemical or physical processes. Direct energy deposition (DED) or powder bed fusion (PBF) can be used as additive manufacturing processes in which metal powder or wires are used to print dense metal layers on substrates or on freeform surfaces of existing components [1]. Metal powder (pure elements, element mixtures, master alloys) or metal wires are melted at high speed and instantaneously deposited in layers on respective metallic substrates. In case of the so-called laser cladding [2], this technology is generally used for applying coatings or for tool repairs. Compared to subtractive processes, additive processes save time and resources, as the material is only added where it is needed. Established steels, nickel-based alloys or titanium alloys are typically used. However, it is also possible to obtain completely new materials by in-situ alloying of powder mixtures or to create material gradients by changing the powder mixture composition during the build-up [3]. High entropy alloys (HEAs) represent a new research field for future applications. ... mehrThese are formed from a large number of elements, all of which are present in similarly strong concentrations e.g., alloys consisting of zirconium, niobium, hafnium, tantalum or tungsten [4]. The alloys formed can generally be single-phase as well as multi-phase mixed crystals. HEAs can often combine high strength and very good ductility. In-situ alloying offers the unique possibility of fast material screening for the future production of new metallic components with outstanding mechanical properties at high temperatures. For a long time, the manufacture of refractory alloys was limited to vacuum arc remelting because of their high melting points. With laser-based methods, these metals are locally melted by the focused laser beam and deposited additively. In addition to material development, additive manufacturing offers great design freedom in component design, which can be used, for example, for the development of load-optimized designs based on the bionic principle [5].
To add up to the versatility of additive manufacturing, laser post-processes can be used to modify the resulting surfaces of parts produced with such technology [6-9]. The different types of laser sources commercially available assure their suitability in a wide range of applications, with continuous wave (cw) lasers being often used for reduction of surface roughness, while pulsed lasers being applied in the modification of surface functionalities and to enhance the geometry accuracy. Even with the prospect of being able to replace certain steps of the additive manufacturing process chain, adopting laser post-processes as an additional step can also be proved beneficial when specific characteristics are required in localized areas of the final built components.