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Weldability of various materials

Weld of aluminium parts

The possibility to join metal parts by fusion welding depends first of all on their metallurgical properties. This problematic is extremely wide, therefore, in this paper, we shall restrict our interest to only some specific questions, more important for our needs. Apart from those classical, commonly used materials, also some exotic ones, applied mainly in new branches of research and industry are also needed. This needs accelerated in the second half of 20. century the development of new methods of welding, applying laser or electron beam. The welding by electron beam in vacuum proved to be the most suitable, if not the only one applicable method for welding some materials.

Electron beam welder MEBW-60/2

E-beam welder MEBW-60/2

In the year 2005 the representatives of a German firm expressed their interest to include one of our electron beam welders into their production program. It was agreed that building of the prototype will be started at the beginning of the next year, but soon was realized that the existing documentation needs to be thoroughly revised and digitalized. It was also clear that the current electronics is outdated and must be substantially renewed, if it should meet our new demands and the EU standards.

Basic features of electron beam welding

Profily typických svarů elektronovým svazkem

The kinetic energy of fast moving electrons can be utilised as a source of heat for welding. The free electrons in vacuum can be accelerated by electric field and formed by magnetic lens into a narrow ray carrying high energy, which is transformed into heat at the spot of impact. Thanks to high power concentration (e.g. 104 mm−2) the velocity of temperature increase in the spot of impact is extremely high, making any material melt very rapidly. Consequently, the electrons penetrate rapidly into the material, so producing a deep but narrow weld. Using high enough power, the depth of electron penetration can be as high as e.g. 10 cm in stainless steel, at the depth to width ratio up to 30:1.

Atmosphere density in the space where electron beam is generated and formed must be as low as possible. Also in working space of electron beam welder high vacuum is preferable. Electron beam generator (electron gun), vacuum working chamber, vacuum pumping system, high voltage power supply and control electronics are inevitable parts of each electron beam welder. That's why electron beam welders are very expensive. The acquisition costs may be compensated by low operation costs by some applications, like in mass production. Electron beam in vacuum may be inevitable in some cases, e.g. if highly reactive metals like Titanium or Zirconium, are to be welded.

The construction and dimensions of the working chamber are to be adjusted individually to the dimensions of welding parts. Their volume may vary between litres and hundreds of cubic meters. The EB welders in our laboratory are small sized – the bigger one has capacity about 150 litres, the smaller ones about 7 litres.

Vacuum furnace PZ 810

Working chamber of vacuum furnace PZ 810

Modernized vacuum furnace PZ 810 produced by former company Tesla. The furnace has vertical cylindrical chamber.

Single-pin vacuum feedthrough

Single-pin vacuum glass-sealing feedthrough. The feedthrough can be electron-beam welded, e.g. into custom flange. Its operational temperature range is –196°C to +400°C. It can be used for UHV.

Multilayer X-ray Optics - Periodic X-ray multilayers

We deposit X-ray molybdenum/silicon multilayer system, which can be used in the range from about 12 – 30 nm. Peak reflectance values are approaching 70% for normal incidence.

At very short X-ray wavelengths (wavelengths below about 4 nm) efficient normal incidence multilayers cannot be produced because interface roughness cause too much reduction in the reflectance. However periodic multilayers can still be used at near grazing incidence. They provide high reflectance at graze angles that are much larger than what can be achieved with single-layer coatings.

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