Build-up strategies for additive manufacturing of three dimensional Ti-6Al-4V-parts produced by laser metal deposition

Abstract

Laser metal deposition (LMD) has been applied as a coating technology for many years. Today, the technologies capacity to produce 3D depositions leads to a new field of application as additive manufacturing method. In this paper, 3D laser metal deposition of titanium alloy Ti-6Al-4 V is studied with special regard to the demands of additive manufacturing. Therefore, only the coaxial LMD powder nozzle is used to create the shielding gas atmosphere, which ensures high geometric flexibility. Furthermore, specimen with high aspect ratio and hundreds of layers are manufactured, which represent typical features in additive manufacturing. The presented study contains the following steps: First, cylindrical specimens are manufactured with a standard shell-core build-up strategy and mechanical properties as well as fracture mechanisms are determined. Based on the results, experiments are conducted to improve the build-up strategy and new tensile test specimens are built with the improved strategy. The improved strategy incorporates variable track overlap ratios to achieve a constant growth in the shell and core area. As blanks, lean cylinders comprising more than 240 layers and a height of more than 120 mm are manufactured. The specimens are analyzed by X-ray inspection for material defects. Fractured surfaces are observed via scanning electron microscopy and the composition of the surfaces is determined using energy dispersive X-ray spectroscopy. The tensile test results prove mechanical properties close to ASTM F1108 specification for wrought material. V

Characterization of Ti–6Al–4V Fabricated by Multilayer Laser Powder‐Based Directed Energy Deposition

“…The additively manufactured Ti–6Al–4 V blanks under investigation are fabricated via laser powder‐based directed energy deposition (DED‐L) with local protective gas atmosphere using the improved shielding + carrier gas protection and the optimized deposition strategy presented by Spranger et al [ 10 ] The DED‐L blanks are cylinders with 123 mm height and 18 mm target diameter and 240 layers. Five cylinders are built‐up in one batch.…”

“…The minimum strength requirements are achieved in all studies, but this does not necessarily apply to the elongation at fracture, especially in the study of Yu et al [9] For a fair comparison with the work of Spranger et al, Table 1 shows values from the work of Carroll et al from tensile samples oriented parallel to the BD and not exposed to oxygen. [10,12,13] The work by Spranger et al is relevant in terms of transferability to laser metal deposition applications in AM, and its results in terms of mechanical properties are promising. [10] Therefore, we follow up on that study by further investigating the obtained properties and process quality.…”

“…[ 7,8 ] Increasing their content usually leads to increased strength and hardness and reduced ductility. [ 9,10 ]…”

“…The work of Spranger et al focuses on improving the shielding gas protection and adapting the cooling cycles to control the temperature regime during multilayer deposition. [ 10 ] Furthermore, they optimize the travel path strategy and achieve uniform volume growth over hundreds of layers. After the manufacturing process, they do not apply any further heat treatment.…”

“…The minimum strength requirements are achieved in all studies, but this does not necessarily apply to the elongation at fracture, especially in the study of Yu et al [ 9 ] For a fair comparison with the work of Spranger et al, Table 1 shows values from the work of Carroll et al from tensile samples oriented parallel to the BD and not exposed to oxygen. [ 10,12,13 ]…”