Material efficient production of functionally graded materials using coaxial laser double-wire directed energy deposition

Abstract

The coaxial Laser Double-wire Directed Energy Deposition (LD-DED) process is capable of providing two wire materials simultaneously into a common processing zone. Thus, in-situ production of alloys in a local manner or across the entire sample can be realized with the characteristic high material utilization of the laser wire Directed Energy Deposition (DED) processes. Fabricated samples show a homogenous distribution of alloying elements across single welding seams enabling a functionally graded transition zone along multi-layer samples. This work shows the potentials of the LD-DED process for the production of Functional Graded Materials (FGM). Therefore, the process is displayed and single welding seams are examined regarding the element distribution along the seam with a graded material distribution. The samples are produced with a horizontally graded material transition using 1.4430 and 1.4718 stainless steel wires. All samples are fabricated using the multiple Diode Coaxial Laser (DiCoLas) processing head of the Laser Zentrum Hannover e.V. The processing head provides the materials under a small angle of incidence and utilizes three fiber coupled laser diodes to supply the necessary thermal energy for the melting process of the base and wire materials. Using Energy-Dispersive X-ray spectroscopy (EDX) line-scans and mappings to determine the element constituents along the cross-section, a graded transition of elements in the horizontal direction can be detected. Images captured with a Keyence VK-X1100 3D-laser-scanning microscope provide information of the cross-section quality regarding material defects and surface quality. Furthermore, the Vickers hardness progression along the building direction is measured.