In-situ & in-operando additive manufacturing of engineering alloys

Abstract

Laser-based metal additive manufacturing (LAM) techniques are innovative processes that permit the fabrication of near net-shaped metallic components with complex geometries However, there are still several scientific issues that need to be overcome in regards to understanding processing mechanisms and microstructure control. Moreover, the lack of metallic alloys tailored to the metallurgical conditions of LAM is still a critical bottleneck for the disruptive manufacturing technology of AM. Among LAM techniques, the two promising processing methods Laser Powder Bed Fusion (LPBF) and Laser Directed Energy Deposition Additive Manufacturing (L-DED) have been used for “quasi” in-situ synchrotron x-ray computed tomography and in-operando synchrotron x-ray radiography experiments on novel Al and Ti alloys tailored for AM. L-DED is one of the leading techniques for larger components and some specialist applications and has been recognised in international standards. The promise of L-DED is based on its high deposition rate compared to other LAM methods and its utility in the remanufacture, modification and repair of high value components. While initial laboratory investigations show that Ti-Fe alloys can achieve mechanical performance beyond that of conventional alloys, the fundamental mechanisms of strengthening, grain refinement and laser coupling need to be investigated to optimise processing. In-operando L-DED experiments for different variations of the Ti-Fe alloy system during synchrotron X-ray radiography were performed at the ESRF beamline ID19 with a frame rate of 20kHz. First results allowed to obtain information on the melt pool geometry, hot crack formation and healing below the melt pool, powder particle distribution as well as porosity inside the powder particles and their evolution inside the melt pool. LPBF is an innovative process that permits the fabrication of near net-shaped metallic components with complex geometries and higher material efficiency, typically replacing multiple conventional components with savings in material, tooling and assembly costs. The LPBF process for the novel structural Al-Fe-Zr alloy, Aheadd® CP1, by Constellium was investigated in-situ during synchrotron x-ray microtomography at the ESRF/BM18 beamline using a miniature LPBF machine. The data obtained provides information on defect morphology and size distribution, as well as build quality as a function of printing strategy and geometry. Moreover, information about the porosity history from layer to layer that cannot be easily obtained by other methods was acquired. It was observed that the LPBF process is a partially self-healing process, i.e., pores formed in one location can heal after a few more layers are built up, while other pores form. This experiment allows for the understanding of the underlying mechanisms and provides suitable data, such as morphology and distribution of defects depending on material, printing parameters and sample geometry, for the validation of AM simulation models.