Banca de DEFESA: RAYSA CRISTIANO PAULINO PEREIRA

STUDY OF GRAPHITE WETTING VIA METALIZATION ROUTES WITH ACTIVE ELEMENTS

brazing, wettability, active element, vanadium, titanium, metallization

The production of dissimilar metal-ceramic joints has been a field of interest in developing aerospace technologies, with brazing being an important technique for joining these substrates. The brazing process is particularly challenging when joining carbon-based components, such as graphite, due to the non-wetting of its surface by filler metals. To study the promotion of wetting of this substrate by the filler metal Ag-28Cu, two active elements were defined: titanium and vanadium. The substrate surfaces were prepared before the wetting test using different metallization routes. Three surface preparation routes were used: ROUTE 1 – metallization by magnetron sputtering; ROUTE 2 – metallic powder with a volatile solution; ROUTE 3 – metallic powder with organic binder. For each route, the compositions deposited on the samples were composed of vanadium, titanium, or combinations of both. As a result, samples produced via ROUTE 1 did not achieve wetting effects (characterized by θ < 90°). Samples with vanadium thin films, 0.50 μm thick, allowed the interaction of the filler metal at the interface, with contact angles greater than 120°. For ROUTES 2 and 3, vanadium implemented alone on the graphite surfaces did not result in interaction with the filler metal and the graphite substrate. However, samples produced from the titanium and vanadium mixture (50% by weight of each) resulted in adequate wetting, especially for ROUTE 3, with thermal cycles of 1000 °C (for 20 minutes of isotherm). The microstructural analysis indicated the production of Ti-V-C compounds in the reaction zone and Ti-V phases in the filler metal, indicating a reduction of Cu-Ti phases, undesirable when they have high hardness and brittleness.