Titanium is a tremendously useful metal and very abundant, yet only 186,000 tonnes (205,030 tons) of it are produced a year and it’s not used very much outside of the aerospace field because it’s so expensive and difficult to forge. To correct this, a team led by André Albert at the Fraunhofer Institute for Surface Engineering in partnership with Thin Films (IST) in Braunschweig, Germany have developed a new process for hydroforming titanium at high temperatures in a single step that promises to make titanium more of an everyday material.
Titanium is wonderful stuff. It’s strong, lightweight, non-magnetic, remarkably corrosion resistant and it’s the ninth most common element on Earth. It’s perfect for aircraft, medical implants, surgical instruments, marine components and ridiculously light and strong spectacle frames. By rights, it should be as commonly employed as iron and aluminum, but it’s still so rare in everyday life that it’s used in jewelry in a way that aluminum isn't.
The problem is that titanium, for all its virtues, is very tricky to fabricate. For example, it melts at an impressive 1,668º C (3,034º F), which is great for supersonic aircraft. However, titanium catches fire at 1,200º C (2,190º F) and it will not only burn in air, it will even burn in nitrogen.
Worse, it’s a bit “sticky” when hot. According to André Albert, group leader for media based forming technologies at the Fraunhofer Institute for Machine Tools and Forming Technology (IWU) in Chemnitz, Germany, “titanium tends to adhere to the forming tools. This leads to major damage which can cause components to fail in the worst case scenario. This effect is amplified by the extremely high temperatures of up to 800º C (1,472º F), at which titanium has to be formed.”
What this means is that titanium is mostly worked by cold forming at low temperatures and then reheated to remove the resulting defects. Referring to the manufacture of car exhausts, Albert said, “forming titanium at room temperatures leads to severe cold work hardening of the processed pipe. In order to prevent cracking, the metal requires frequent treatment by means of recrystallization processes. This leads to extremely complex multi-stage forming processes which are not economically viable in large-volume production of exhaust systems. This microstructural change can be avoided at extremely high temperatures.”
Albert’s solution to these problems is a new hydroforming process using a 1.40 x 1.20 meter (55.11 x 47.24 in) forming tool made of nickel-based alloys that remain stable at over 800º C (1,472º F) without oxidizing. It’s coated with a special film a few micrometers thick that keeps the hot titanium from sticking to the tool.
Because titanium is so flammable, the process needs to be conducted in a special neutral gas atmosphere, but it means that titanium products like exhaust pipes can be forged by hydraulic pressure in a single step and in one place without cracking. Needless to say, this results in great savings.
Fraunhofer will be presenting the initial results of the project at the EuroBlech trade fair, October 23 to 27 in Hannover, Germany. If the promise of the new process works out, we may see titanium used for more things than fighter jets and sporks in the near future.
Source: Fraunhofer
