It is no surprise that many things that are supposed to be good and allowed to be expensive are made of titanium. Components for the automobile and aerospace industry, implants, bicycles, jewellery and even building facades, such as on the world famous Guggenheim Museum Bilbao.
The company GfE Metalle und Materialien defines itself as one of the worldwide leading manufacturers and providers of high-performance metals and materials. In the Coating Materials division, sputter targets, arc cathodes and sputtering materials are produced using powder metallurgy for a wide range of coating techniques. One of the most well-known applications is the coating of tools made of hard metal for machine processing, which are made harder and more wear-resistant due to the layers that are often only a few µm thick. In other applications, architectural glass is AR coated and protected from adverse weather effects, electrical appliances are shielded from electrical and magnetic fields, conducting paths are constructed or implants made of plastic or metal acquire the necessary biocompatibility.
GfE developed HDH technology, among other things for the manufacture of high purity titanium powder, which is used in medical technology. HDH stands for hydration – dehydration, which means that through the addition of hydrogen, the source material becomes brittle, and can be crushed mechanically. After this process step, the material is returned to its original state in a thermal process under a high vacuum.
Since titanium, which in medical technology is used for coating and implants, may not contain any ferromagnetic material whatsoever, tiny particles of iron, which rub off the grinding media during the crushing process, are now removed from the batches in an acid etching bath, and the batches are then dried in the vacuum drying oven. The process needs to take place in a vacuum, since titanium has a high bonding affinity with oxygen, and the metallic purity of 99.7% could not be achieved in a standard drying oven. The two Memmert appliances run for 12 to 14 hours per day and evacuate three to four litres of water in each drying process. “This job is a real chore”, laughs Peter Muntau, an employee in the titanium powder production line at GfE. “We cannot afford any production stoppages, which is why the robustness of the vacuum oven is absolutely crucial. And the technical service of Memmert is always immediately on hand for the necessary replacement of wear parts.” The drying times vary, depending on the amounts and particle sizes, which is why the technicians at GfE like to use the Memmert chip card to simply start the stored programme sequences.
HDH technology enables the morphology, that is, the shape of the grain, to be precisely defined. The Jülich Research Centre made use of this property when it patented a procedure for the manufacture of highly porous titanium shaped bodies for biomedical applications in 2002.
With the Jülich procedure, it was made possible to compress a mixture of the GfE titanium powder and a suitable buffer, in this case sodium hydrogen carbonate, so hard that the pressed shaped bodies could be processed mechanically before the sintering process. To guarantee the stability of the pressed part, the titanium particles must interlock during the pressing procedure. For this purpose, precisely defined square particles were required, spherical titanium powder was not suitable, however.
After the forming operation, the buffer is decomposed in air at temperatures below 100°C, leaving behind defined pores. The resulting porous titanium shaped body is provided with stability through a final sintering process. In the finished implants, the porosity allows the bone to be incorporated, thus guaranteeing the attachment of the implants in the human body.
An overview of focus topics
Picture credit: Forschungszentrum Jülich, fetcaldu@sxc.hu, GfE Metalle und Materialien
