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6859 |
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Tuesday, March 09, 2021, Hall 1 3:45 PM Surface Treatment |
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Improvement of the surface properties of light metals by electron beam additive technique |
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Stefan Valkov* / Institute of Electronics, Bulgarian Academy of Sciences, Bulgaria Peter Petrov / Institute of Electronics, Bulgarian Academy of Sciences, Bulgaria |
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Light metals, such as titanium and aluminum, as well as their alloys are widely used in the field of the modern aerospace and automotive industries, etc. due to their excellent resistance to corrosion, high stiffness and toughness and remarkable strength-to-weight ratio. However, some drawbacks due to the low hardness and poor wear resistance can be mentioned and the applications of these materials are still limited. The discussed limitations depend mostly on the surface properties of the materials, and they can be overcome by an appropriate surface modification. Currently, the electron beam treatment techniques are among the most promising methods for surface modification. In this work we report an electron-beam additive technique for alloying of Ti and Al substrates with Al/Nb and Ti/Nb bilayer coatings. The alloying materials were applied on the surface of the substrates by physical vapor deposition (PVD) techniques and after that the specimens were then subjected to electron-beam alloying. Afterwards, on the already formed surface alloys, the same alloying elements were deposited by the same techniques and the samples were again subjected to electron beam alloying. This procedure was repeated several times in order to form intermetallic phases. The experiments were carried out on Leybold-Heraeus equipment. The accelerating voltage (U) was 52 kV, the beam current was from 10 mA to 30 mA, the electron beam scanning frequency was from 1 kHz to 10 kHz. The beam diameter was 0.5 mm. The obtained phase composition was studied by X-ray diffraction. The experiments were performed in symmetrical B-B (Bragg-Brentano) mode using Cu K? (1.54Å) characteristic radiation. The patterns were registered in the range from 20° to 80° at 2? scale, with a step of 0.02° and counting time 3 s per step. The microstructure was studied by scanning electron microscope equipped with EDX microanalyzer. The EDX detector integrates a true standardless analysis with P/B ZAF quantitative corrections (Z being the atomic number correction factor; A–X-ray absorption correction factor; F–fluorescence correction factor. The measurements of the microhardness were carried out using theMicro-Duromat 4000 device of the company Reichert-Jung, with a loadof 30 g, time 10 s and gradient 10 g/s. The structure and properties of the obtained surface alloys are discussed concerning the applied technological conditions, phase composition and microstructure. |