Nanoparticle improved metal materials for additive manufacturing

A variety of laser systems and powder materials is available for additive manufacturing processes such as powder bed fusion of metallic parts (laser beam melting). The required energy density for a sufficient melting of powder materials strongly depends on the optical properties of the used powder (e.g., absorption, reflection and transmittance). During laser irradiation a moving melt pool is generated in the laser heat affected zone. Re-solidification of the molten particles results in interconnected welding lines similar to those of traditional welding processes. Here, the layer by layer approach combined with a selective laser exposure in cross-sectional areas of the parts enable the generation of 3D structures from the powder bed. The mechanical properties of such fabricated structures are usually comparable to the mechanical properties of the bulk material the powder particles are made of. In this paper, a proof of principle is demonstrated to receive improved mechanical or other properties of parts being manufactured by laser beam melting. The approach addresses laser beam melting of the commonly available powder materials tool steel (1.2709) and Hastelloy X (2.4665) which are additionally modified with nanoparticles (Al₂O₃) on their surfaces. Due to the shortage of these two available nanoparticle modified materials (about 100 g each) only relatively small test specimens are manufactured and, therefore, only limited typical characteristic values could be determined. However, the nanoparticle modified and laser beam molten 3D structures were systematically characterized by optical and scanning electron microscopy, energy-dispersive X-ray microanalysis, micro hardness indentation and etching analysis. It turns out that modification of the educt powder surfaces with nanoparticles prior to laser beam melting can improve e.g., mechanical properties of the generated 3D structures.