Austria’s only electron beam welding facility for basic research at the Institute of Materials Science and Welding at TU Graz, commissioned in 2012, is a Jack of all trades: apart from welding up to 150 mm thick steel and micro components, it can also produce alloys and treat surfaces. This process makes welding many times faster than the conventional arc welding. Welding tasks that used to take several hours or even days are now accomplished in a matter of minutes. In addition, the low heat input means that distortion and heat affected zone is minimal. As a result little or no reworking is required for the welded components, which reduces costs.
Comparison between conventional arc welding (left) and electronic beam weld. Using the electron beam, materials can be welded in a single layer without filler material. Due to the concentration of heat, the welding zone is a very narrow.
But how does this technology work? First, the electrons are shot against the workpiece at up to 2/3 of the speed of light. When they hit the material they are slowed down abruptly. The kinetic energy is transformed into thermal energy, which heats the component. "Using magnetic fields, we can deflect the high-energy electron beam within fractions of a second. As a result the beam can be controlled so precisely that the system is capable of creating predefined surface structures in the micrometre range, which allows us to modify the mechanical and geometrical properties of the topmost layer of materials. This would be impossible with a conventional welding system," explains Norbert Enzinger, group leader at the Institute of Materials Science and Welding (IWS) at TU Graz.
The electron beam welding facility at TU Graz offers unique possibilities for processing a wide range of materials. The facility, which costs EUR 1.3 million and has the size of a room, was financed by TU Graz, the Science Department of the Province of Styria and EU funds.
A driver of innovation in medicine
Electron beam surface treatment is particularly interesting for innovations in the field of medical engineering. In cooperation with the Department of Orthopaedics and Orthopaedic Surgery at the Medical University of Graz, the Institute of Materials Science and Welding at TU Graz is working on a new generation of implants. Currently the insertion of implants may lead to complications such as postoperative infections. This is due to the low degree of adherence of the tissue to the implant material and implant slipping. As a result the tissue is irritated and a cavity is formed in which bacteria can spread. "However, we can now improve the adherence of the tissue by manipulating the surface structure of the implant," says Claudia Ramskogler from the Institute of Materials Science and Welding, who is researching this topic. "With electron beam technology we are able to uniquely treat the surface structure of the metallic material, in this case titanium alloys."
Scanning electron microscope image of a cell cultivation (osteoblasts MC3T3 E1) after 24 hours on an electron beam-structured surface. Material: Commercially pure titanium (TiGr2).
Initial tests with cell cultures that look at the implant surface following the colonisation with cells have already given very promising results. The researchers are presently tinkering with a special coating of the surface to further improve biocompatibility.
Power plant construction and similar applications
The thick-walled parts of the power stations are exposed to enormous steam pressures and temperatures – a formidable challenge for materials research, and on that will further increase as the world’s energy demand keeps growing. If the efficiency of the power stations is to be improved any further, the steam pressure and the temperature in the power stations needs to be increased. This will require materials able to withstand these conditions. One possibility would be to continue relying on relatively inexpensive high temperature-proof chromium steel for the manufacture of most power station components, while temperature and pressure-critical parts could be made of the so-called nickel basis superalloys. Until recently, the question was whether it is possible to achieve a "power station-proof" welding joint between these superalloys and chromium steel. This is precisely where the electron beam welding system comes in. On a commission of the Traisen foundry – a Voest-Alpine company – the Institute of Materials Science and Welding at TU Graz showed that electron beam welding is a very suitable technique to join these two materials. The 50 mm thick welding seam successfully passed the subsequent standardised tests, and the welding process took less than one minute.
The electron beam welding facility can also be used for the production of alloys. The Institute of Electron Microscopy and Nanoanalysis at TU Graz produced a nickel copper alloy that was then used for further material analyses. "We are still experimenting with several materials in this field, the system might conceivably even be suitable for the production of alloys from any number of elements," explains Coline Béal, university assistant at the Institute of Materials Science and Welding at TU Graz.
Electron beam technology is also finding its way into automotive industry, for example for gearboxes, and high-end applications in the fields of aviation and aerospace. "Distortion-free welding of small parts is also possible here – this would not be possible with conventional welding methods," states Norbert Enzinger. At the same time, feasibility analyses for many other applications are also being conducted.