From Production Waste to Raw Material
The RWTH Institute of Process Metallurgy and Metal Recycling conducts research on efficient and cost-effective methods for the production and recycling of titanium aluminide.© Peter Winandy
“This is the result of our work,” says Janik Brenk from the Institute of Process Metallurgy and Metal Recycling, IME for short, which is headed by Professor Bernd Friedrich.
The doctoral candidate points to a bar-shaped object, about 150 cm in height, which is positioned next to a steel beam in IME's large manufacturing hall. It consists of titanium, the base material for the turbine blades of jet engines.
It is a material that is high in demand: it is light-weight, robust, and it can withstand high temperatures. RWTH has been developing efficient and cost-efficient methods for the production and recycling of titan aluminide for several years now. In the manufacturing of turbine blades, 90 percent of the material used becomes waste. And the turbines have a service life of between 10,000 and 20,000 hours of flight before being replaced.
Thus there is sufficient material for the lab experiments conducted at the institute located in Intzestraße – it is provided by Access, an affiliated institute of RWTH Aachen. “In our work, we focus on two approaches – the manufacturing of titanium alloys and their recycling,” explains Janik Brenk.
Kaiserpfalz Award for RWTH Metallurgists
RWTH has longstanding experience and expertise in the two processes, and earlier this year it was presented with the Kaiserpfalz Award by WMV, the German Metal Industry Federatrion. The prize, which is worth 50,000 Euros, was awarded for developing a concept which minimizes costs in the production of titanium alloys.
The researchers have now perfected the process so that compared to conventional technologies, several steps in the production process can be skipped and thus the production costs significantly reduced.
"The principle of our new approaches are not entirely new,” explains Brenk. “However, we are very good concerning composition and process control.” Titan is a material that is hard to process – it oxidizes as soon as it gets in touch with oxygen. For this reason, it can only processed in a vacuum or under special protection.
At RWTH, the researchers are using a large induction furnace, in which the production waste is melted at a temperature of 1,600 degrees Celsius and subsequently cast into bar-shaped molds. With the help of calcium, the oxygen bound in the melt is transformed into lime, which floats on top of the melt and can be skimmed.
To ensure that the material is as pure as possible, in a next step, the material is melted once more in a vacuum arc melting furnace, which makes it possible to remove all remnants of calcium and gaseous impurities. Using the resulting material, turbine blades can be manufactured that weigh only about half as much as conventional nickel alloys.
Getting Ready for the Market
The Aachen recycling process is tested in a final stage before it can be brought to market. Currently, the process is being prepared for large-scale application together with partners from industry. According to Janik Brenk, the process could be ready for the market in about five to ten years.
Both the primary and the recycling processes can be applied in the aviation industry, but also in the automotive industry, in the production of turbochargers, for example.