Wire-based electron beam additive manufacturing of tungsten

In present study, the feasibility of wire-based additive manufacturing of commercially pure tungsten using electron beam technique could be demonstrated. Three different representative volumetric AM structures were built and subsequently characterized. The parts show a sound visual appearance with the absence of macroscopic cracks or severe distortion. The fabricated parts exhibit high density and the value depends on the welding sequence applied; while the thin- and medium-walled structure has a relative density of -100% and 99.875%, the measured relative density of the volumetric structure is slightly reduced to -99.131% due to the smaller periodic bonding defects. However, a higher density could be achieved compared to powder-based processes on refractory metal. The mean hardness value of the fabricated AM structures is approx. 366-380 HV1 and is in the range of approx. 89-93% of the conventionally fabricated substrate of 410 +/- 39 HV1. A coarsening of the grains from the bottom to the top and a change in morphology can be noted for all AM structures. While the coarsening is quite severe for the thin-walled structure, it is moderate for the volumetric AM structures due to the change of the thermal boundary conditions. Caused by the deposition process, the microstructure in the substrate also changes and exhibits a coarse-grained heat-affected zone. Nevertheless, the grain size is still smaller compared to the AM bulk material.

Automated summary

In this study, the feasibility of wire-based additive manufacturing of commercially pure tungsten using electron beam technique was demonstrated, achieving high density and hardness values. Different AM structures showed different characteristics in terms of appearance and density, with grains coarsening from bottom to top.