José L. Rodríguez-Galicia

High Temperature Chemical Interaction Between SSiC Substrates and Ag-Cu Based Liquid Alloys in Vacuo

The interfaces formed at 850 °C under vacuum between polished or oxidized substrates of pressureless sintered α-SiC (SSiC) and Cusil, Cusil-ABA and Incusil-ABA brazing alloys have been characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. No chemical interaction is observed for Cusil on both SSiC substrates. In contrast, the Ti contained in the Cusil-ABA and Incusil-ABA alloys promotes the occurrence of chemical reactions at the metal/ceramic interface with both SSiC substrates. The formation of TiC and Ti5Si3 is observed for Cusil-ABA and Incusil-ABA on untreated SSiC, following the sequence SiC → TiC → Ti5Si3 at the metal/ceramic interface. The formation of Ti5Si3 and Cu3Ti3O, following the sequence SiC → Ti5Si3 → Cu3Ti3O, is observed for both Ti-containing alloys on pre-oxidized SSiC. During the wetting experiments, Ti5Si3 and Cu3Ti3O detach from the ceramic surface, floating away from the ceramic/metal interface into the liquid alloy, where the latter phase partially dissolves. It is concluded that for both Ti-containing alloys in contact with pre-oxidized SSiC, the Ti remaining after the reaction with the silica film is insufficient to decrease the contact angle to the values observed for untreated SSiC or to produce a strong metal/ceramic joint.

Titanium Coatings on AISI 316L Stainless Steel Formed by Thermal Decomposition of TiH 2 in Vacuum

Ti-coated AISI 316L stainless steel, for potential biomedical applications, is obtained by thermal decomposition of TiH 2 under vacuum. The presence of hydrogen in the coating material facilitates the sintering process of Ti particles, with simultaneous formation of several inter-diffusion layers at the substrate/coating interface, whose thickness and chemical composition depend mainly on the treatment temperature. Coatings prepared at 1100°C exhibit formation of a wide zone at the substrate/coating interface, which is associated with the appearance of cracks, and which consists of a mixture of λ + χ + α-Fe phases. Formation of abundant microporosity is also observed in this region, which is attributed to the Kinkerdall effect.