Driven by the development of high-strength titanium alloys, the demand for large-volume, complex titanium components or prototypes is also increasing [1
]. Due to the special properties of titanium, such as extremely poor heat conduction, high strength, tendency to form built-up edges [2
], the machining of such components from the solid is only advisable to a limited extent. These disadvantages are reduced by the use of additive manufacturing (AM) technologies. AM enables quick and flexible production of complex, high-strength titanium components in near-net-shape.
The layer by layer production of components from formless material, as opposed to subtractive or formative manufacturing methodologies, is called additive manufacturing [3
]. Materials like titanium with an exceptional strength to density ratio and at the same time limited machinability are used particularly frequently in this field. Beam-based powder bed processes, such as selective laser melting (SLM), LaserCUSING®
or electron beam melting (EBM) [4
], currently dominate the market for components of smaller dimensions [1
]. These processes are characterized by high final contour proximity and a richness of detail. Disadvantages are the limited construction volume and the low build-up rate per time unit [4
Larger components (m
> 10 kg [9
]) are manufactured mainly by directed energy deposition processes, such as electron beam additive manufacturing (©Sciaky) and rapid plasma deposition (©norsk titanium) [10
]. Further, laser welding [14
], tungsten inert gas welding (shape metal deposition) [15
] and gas metal arc welding (wire and arc additive manufacturing—WAAM) processes [9
], using wire as filler material, are widely used. Powder-based freeform processes, like direct metal deposition (DMD), laser engineered net shaping (LENS) or laser metal deposition (LMD) are also part of the current state of the art regarding the additive manufacturing of large titanium components [18
]. Hybrid processes as a combination of SLM and WAAM also exist. Here the laser process is used to manufacture the base plate and the part is built by WAAM [20
In the presented work, the advanced freeform and arc-based additive 3D plasma metal deposition (3DPMD) process was used to produce titanium components. 3DPMD is a further development of the classic plasma transferred arc welding process. Low demands on the powder characteristics (particle size, surface structure), high deposition rates () and the possibility of mixing up to four different powders simultaneously during the build-up process are the most significant benefits of this process.
Detailed information on the process, the materials that can be processed and application examples have been published elsewhere [21
The aim of the work was to demonstrate the suitability of the novel process 3DPMD for the additive manufacturing of titanium components through the determination of the part properties. For this purpose, the external shape of the produced AM-part was evaluated. Subsequently, metallographic cross-sections were prepared, the microstructures were analyzed, the chemical composition of the components was determined, and micro tensile tests were carried out. Near-net-shape capability, homogeneity, microstructures and tensile tests properties were evaluated.
Conceptualization, K.H.; methodology, K.H.; validation, K.H and A.N., formal analysis, K.H.; investigation, K.H. and A.N.; writing—original draft preparation, K.H.; writing—review and editing, K.H.; visualization, K.H.; supervision, A.H.; project administration, P.M.
This research received no external funding.
Conflicts of Interest
The authors declare no conflict of interest.
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Experimental setup for 3D plasma metal deposition (3DPMD).
Characterization of the titanium powder morphology. (a) particle size: d = 125–335 µm; (b) the coarse, sharp-edged and blocky structure.
Manufactured part (a) as-welded condition (b) brushed condition.
Overview and optical micrographs of the part at different locations, in: As-welded condition, (a) overview of the AM part, (b) Ti6Al4V build plate, (c) structure of the upper layer, (d) detail structure of the upper layer, (e) structure of the bottom layer, (f) detail structure of the bottom layer.
Overview of the influence of the loading direction on the tensile strength, condition: As-welded, (a) schematic of the tensile test specimen orientation, (b) results of the tensile tests.
Material spectrum of the base material analyzed with EDX.
Overview and optical micrographs of the weld metal in different conditions, (a) representative stress-strain-diagrams, (b) representative optical micrographs of the weld metal with mean values of the alpha laths width.
Oxygen content of the base material analyzed by inert gas fusion.
|Ti Grade 4||bal.||<0.30 wt.% |
|Raw material||99.70 wt.%||0.30 wt.%|
|AM Part||98.32 wt.%||0.68 wt.%|
Summary results of the tensile tests (Fmax: maximum strength load, Rp0.2: 0.2% yield strength; Rm: ultimate tensile strength, A: elongation at fracture.
|PWHT||Fmax (N)||Elongation (µm)||Rp0.2 (MPa)||Rm (MPa)||A (%)|
|600 °C/8 h||3256||325||805||832||3.2|
|800 °C/8 h||2762||475||710||732||4.6|
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