Banca de QUALIFICAÇÃO: RAYSA CRISTIANO PAULINO PEREIRA

Study of the wetting of graphite substrates metallized with active metals by Ag-Cu eutectic

 wetting, active element, vanadium, titanium, metallization

The goal of this study is to characterize the vanadium interaction as an active element in the wetting of graphite substrates by the Ag-28Cu filler alloy. The sample surfaces were prepared before the wetting test by adding the active element to them. For the surface preparation phase, three different routes were tested: ROUTE 1 – metallization by magnetron sputtering; ROUTE 2 – use of metallic powder with volatile solution; and ROUTE 3 – use of metallic powder with organic binder. During the different routes mentioned, the titanium and vanadium active elements were added to the surfaces of graphite substrates alone or in combination. Titanium was used as the comparison basis for vanadium, as it is the active element most used for carbon brazing. As a result, samples produced via ROUTE 1 did not achieve wetting effects. Samples with 0.50 μm thickness of vanadium thin films only allowed the filler metal to adhere to the joint, with contact angles greater than 120°. For ROUTES 2 and 3, vanadium resulted in no interaction with the filler metal and graphite substrate. However, samples produced by mixing titanium and vanadium (50/50 ratio) resulted in adequate wetting, especially for ROUTE 3, with thermal cycles of 1000°C in a 20-minute isotherm. The phases and compounds produced in the metallic region for these samples present a high distinction when compared to the ones produced in samples with only titanium.