Characterization of the anisotropic properties for laser metal deposited Ti-6Al-4 V

Laser metal deposition (LMD) connected with milling processes offers the opportunity for an efficient, resource conserving manufacturing for large structural components made from Ti-6Al-4 V. Conventional manufacturing routes for example in the aerospace industry come along with up to 95% of the waste material that has to be machined from the bulk material. LMD is an additive manufacturing process building parts based on nozzle-fed powder by laser solidification. This technology offers unique advantages for the production of near net-shape parts. In contrast to the powder bed-based technologies, it also provides a higher productivity rate. Today, LMD lacks reproducible process strategies manufacturing large parts in narrow tolerances and predictable microstructural properties. The building height of a single layer and the geometrical shape of a three-dimensional shaped part alter progressively with increasing part dimensions, consecutively leading to a higher effort in the manufacturing-process development for such parts. To reduce this effort, in this paper, first the actual state of the anisotropic properties is investigated for LMD-manufactured parts to obtain thorough knowledge of the process and shape-related dependencies with the quality aims. A preliminary experimental investigation of the shape and process-dependent properties such as the microstructure (chemistry changes and grain sizes), mechanical properties (hardness), and geometry (tolerances) is conducted. Based on these results, an in-depth study with optimized parameter sets is carried out to identify the linkage between geometry, process parameters, and the quality criteria of the part, using methods such as light microscopy, inductively coupled plasma-mass spectrometry, Vickers hardness, coordinate measuring, and laser scanning microscopy. For this purpose, representative shaped specimens are manufactured with the LMD-process through different optimized process strategies. The results give the opportunity to evaluate the impact of process parameter changes and the shape on the part quality such as mechanical properties, surface quality, and element loss. This is achieved through identifying the relationship between the input and the output factors from the experimental study, and their importance for part quality is assessed. It is shown that the complex correlation between the process parameters, the part geometry, and the resulting quality can be controlled with suitable process design in LMD-manufacturing of Ti-6Al-4 V parts. Finally, based on the summarized results, an outlook is given on tolerances for different quality aims.

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Characterization of the anisotropic properties for laser metal deposited Ti-6Al-4 V