Additive manufacturing of novel complex tungsten components via electron beam melting: Basic properties and evaluation of the high heat flux behavior

The basic principle of electron beam melting (EBM) technology is the additive generation of structures by the selective melting of metal powder layer by layer with an electron beam under vacuum conditions. The cooling rate of the EBM process can be reduced drastically by increasing the temperature of the powder bed to avoid the formation of solidification cracks by brittle materials such as tungsten (W). This refractory metal is a promising candidate as plasma facing material for future fusion reactors. The selection of tungsten is owing to its physical properties such as the melting point of 3420 °C, the high strength and high thermal conductivity, the low thermal expansion and low erosion rate. Disadvantages are the low ductility, and fracture toughness at room temperature. Furthermore, the manufacturing by mechanical machining, such as milling and turning, is extremely cost and time consuming. An interesting alternative process route to conventional manufacturing technologies is EBM. It allows the near-net shape fabrication of prototype structures with geometrical freedom and has proven its capability for mass production by the manufacturing of hip prostheses made of titanium. This manuscript describes the fabrication of tungsten parts via electron beam melting, with application to the manufacturing of divertor armour. The investigation comprises the microstructure examination, crystallographic texture, as well as mechanical characterization via tensile and Charpy impact testing. This is followed by the presentation of process routes to fabricate mock-ups with different designs and copper cooling structures. Furthermore, the different mock-ups were exposed to high heat flux (HHF) applying transient thermal loads to assess thermal shock and thermal fatigue performance of EBM tungsten. Post mortem analyses were performed quantifying the occurring damage with respect to reference tungsten grades by microscopical means. The achieved results demonstrate the high potential to process tungsten via electron beam melting.