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Electron beam welding at ISI Brno
Dupák, Libor ; Zobač, Martin ; Vlček, Ivan ; Zobačová, Jitka
In vacuum technology, and especially in UHV, we often encounter the necessity of joining\nparts of various metals in combination with the demand for perfect vacuum tightness,\ncleanness of joints and minimum deformations. Electron beam welding belongs to the\nbest technologies capable of fulfilling such requirements.\nThe principle of electron beam welding is based on the transfer of the kinetic energy of the\nincident accelerated electrons to the welded material in the form of heat. The temperature in\nthe spot rises with the beam power density. At power densities as high as 104 - 106 W/mm2,\nthe melted material at the center of the focal point evaporates. This produces a vapor capillary surrounded by melted material that allows the beam to penetrate deeper and melt more material. The speed of the penetration can be much higher than the heat transfer by\nconduction into the surrounding material. This results in narrow melted area and typical knifelike\nprofile of the weld. Thanks to this effect the thermal deformations of welded\npieces are highly reduced to almost none. Small heat affected zone also allows welding near\nheat sensitive parts like sensors, ceramic feed-throughs and brazed joints.
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Small-Volume Reactive Metal Alloys Prepared by Electron Beam Melting
Zobač, Martin ; Vlček, Ivan ; Zobačová, Jitka ; Rek, Antonín
The paper deals with the preparation of small volumes of reactive metal alloys (particularly titanium), utilizing an electron beam as the heat source. The melting was performed in a vacuum environment in order to prevent the compounds from reacting with atmospheric components. The water-cooled crucible avoids any contamination of the alloy, which would have otherwise arisen during the heating of the materials. The composition of resulting alloys were then investigated by energy-dispersive X-ray spectroscopy
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Imaging of SiCN thin films on silicon substrate in the scanning low energy electron microscope
Zobačová, Jitka ; Hüger, E. ; Urbánek, Michal ; Polčák, J. ; Frank, Luděk
The Si-C-N materials have been attracting growing interest due to their excellent physical properties. They are hard, possess a large band gap, resist harsh and high temperature environments, and exhibit interesting nanostrucrures such as turbosrtatic-carbon and nanopores. Their range of application includes anti-erosive turbines and cutting tools, opto-electronic materials, sensors and special drug delivery pharamaceutical products. Most of their interesting properties stems from carbon-nitrogen bonds. Hence, Si-C-N materials with a high content of carbon and nitrogen are of interest. Up to date, the highest carbon and nitrogen content could be synthesised in SiC2N4 and Si2CN4. Both chemical compositions are stable and possess the highest achieved carbon-nitrogen bond. Two different nitride bonding configuration was measured to be present.
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Imaging of thermal treated thin films on silicon substrate in the scanning low energy electron microscope
Zobačová, Jitka ; Mikmeková, Šárka ; Polčák, J. ; Frank, Luděk
Structure of thin films usually requires to be examined on microscopic level. The research topics like growth and stability of thin films, phase transitions and separation, crystallization, diffusion and defect formation has a need for LEED or XPS as techniques adequate for investigation of atomic transport processes on short length scales. The low energy electron microscopy is a complementary solution for imaging of samples with special concern for knowledge of surface physics and material science. In this contribution the microscopic examination of as-deposited and thermal treated thin films on Si substrates is performed.
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