KIT develops industrial scale production process for tungsten parts

Tungsten is the material of choice for the reactor wall surface of ITER’s successor DEMO. The divertor, where plasma impurities and ash from the fusion process are removed, is specifically exposed to extreme heat and particle fluxes. Tungsten is able to withstand such high heat stress, but it is difficult to process. The metal is extremely brittle and, therefore, traditional machining methods such as milling or turning are time consuming and expensive.
Powder Injection Moulding (PIM) offers an alternative. This process moulds a metal powder – mixed with a binding material – under high pressure into the desired shape. After removing the mould, you have a part with near-net-shape precision which does not require further treatment. PIM thus offers a cost-efficient method of mass fabrication that will enable the production of extremely precise metal parts at an industrial scale.
In the last five years, researchers at KIT have successfully adapted the PIM process to be used with tungsten. They produced parts from a microgearwheel 3 millimetres in diameter and with a weight of 0.050 grams, up to a 1.4 kilo plate with the dimensions 60 x 60 x 20 mm. Thus the researchers not only demonstrated the suitability of the PIM process for tungsten, they also showed its scalability and its ability to produce complex shapes with great precision. Another advantage of moulded tungsten parts is the isotropic characteristic of all material properties. Parts machined from plates or rods do not feature such uniaxial grain orientation and therefore do not offer full placement flexibility.

Ideal tool for joining materials

Another issue for DEMO is the joining of tungsten-materials with different doping methods. Doping tungsten with titanium carbide or yttrium oxide enables a wide range of tuning mechanical properties like ductility and strength. Traditional joining methods like brazing would require dedicated materials for the brazing process. KIT researchers have developed a two-component PIM process which enables joints to be produced without any additional materials. KIT is currently developing the PIM process further with respect to producing doted materials and with regard to its suitability for mass production.

Promising test results

The tungsten parts produced by KIT have undergone heat flux tests at FZ Jülich’s electron beam facility JUDITH-1. Thermal shock and thermal fatigue tests have shown promising results. The next step will be studies with respect to plasma-wall-interaction. Divertor parts manufactured for ASDEX Upgrade will be tested there in 2015. Other parts are investigated at the test rig GLADIS at IPP. The PIM process is very flexible and allows a variety of new designs and shapes. The tungsten PIM monoblocks will be assembled into a divertor element and proposed for tests in the WEST experiment in France.